[mlir][PDLL] Add code completion to the PDLL language server

[rriddle]

Summary

This commit adds code completion support to the language server,
and initially supports providing completions for: Member access,
attributes/constraint/dialect/operation names, and pattern metadata.

[jpienaar]

mlir/lib/Tools/PDLL/Parser/Lexer.h

40

This feels special as a token, well even more special than the other markers. Why does it need to be a Token kind?

mlir/lib/Tools/PDLL/Parser/Parser.cpp

255

This seems unrelated to the main change here.

1664

Why an unconditional failure?

mlir/lib/Tools/lsp-server-support/Protocol.h

697

Is this a standard enum? Could we point to the origin? (url to doc)

mlir/lib/Tools/mlir-pdll-lsp-server/PDLLServer.cpp

576

You use .str() on some conversions from twine but not on others,

626

Why `c++ ?

679

of type ?

[rriddle]

mlir/lib/Tools/PDLL/Parser/Lexer.h

40

It's a marker token for when we've reached a code completion location. It doesn't have to be a token, but it's more natural (and less complex) to be one. The modeling here is also kept similar to how this is done in other projects, e.g. this is how clang handles completion as well.

mlir/lib/Tools/PDLL/Parser/Parser.cpp

255

It's used during code completion to provide more accurate completions for the current context.

1664

We just return failure from any completion point to stop parsing. Added a comment.

mlir/lib/Tools/lsp-server-support/Protocol.h

697

Yes, it's from the LSP specification. All of the enums/structs/etc. in this file are based on the specification (and have the same naming). The header comment contains a link to the spec (updated the link in the header given that the location of the spec has changed).

mlir/lib/Tools/mlir-pdll-lsp-server/PDLLServer.cpp

576

This should be fixed now.

626

It provides a nicer presentation of the C++ class of the result's constraint (provides syntax highlighting).

mlir/include/mlir/Tools/PDLL/ODS/Context.h

public:
   /// Insert a new dialect with the context. Returns the inserted dialect, or a
   /// previously inserted dialect with the same name.
   Dialect &insertDialect(StringRef name);
 
   /// Lookup a dialect registered with the given name, or null if no dialect
   /// with that name was inserted.
   const Dialect *lookupDialect(StringRef name) const;
 
+  /// Return a range of all of the registered dialects.
+  auto getDialects() const {
+    return llvm::make_pointee_range(llvm::make_second_range(dialects));
+  }
+
   /// Insert a new operation with the context. Returns the inserted operation,
   /// and a boolean indicating if the operation newly inserted (false if the
   /// operation already existed).
   std::pair<Operation *, bool>
   insertOperation(StringRef name, StringRef summary, StringRef desc, SMLoc loc);
 
   /// Lookup an operation registered with the given name, or null if no
   /// operation with that name is registered.

mlir/include/mlir/Tools/PDLL/Parser/CodeComplete.h

+//===- CodeComplete.h - PDLL Frontend CodeComplete Context ------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef MLIR_TOOLS_PDLL_PARSER_CODECOMPLETE_H_
+#define MLIR_TOOLS_PDLL_PARSER_CODECOMPLETE_H_
+
+#include "mlir/Support/LLVM.h"
+#include "llvm/Support/SourceMgr.h"
+
+namespace mlir {
+namespace pdll {
+namespace ast {
+class CallableDecl;
+class DeclScope;
+class Expr;
+class OperationType;
+class TupleType;
+class Type;
+class VariableDecl;
+} // namespace ast
+
+/// This class provides an abstract interface into the parser for hooking in
+/// code completion events.
+class CodeCompleteContext {
+public:
+  virtual ~CodeCompleteContext();
+
+  /// Return the location used to provide code completion.
+  SMLoc getCodeCompleteLoc() const { return codeCompleteLoc; }
+
+  //===--------------------------------------------------------------------===//
+  // Completion Hooks
+  //===--------------------------------------------------------------------===//
+
+  /// Signal code completion for a member access into the given tuple type.
+  virtual void codeCompleteTupleMemberAccess(ast::TupleType tupleType);
+
+  /// Signal code completion for a member access into the given operation type.
+  virtual void codeCompleteOperationMemberAccess(ast::OperationType opType);
+
+  /// Signal code completion for a member access into the given operation type.
+  virtual void codeCompleteOperationAttributeName(StringRef opName) {}
+
+  /// Signal code completion for a constraint name with an optional decl scope.
+  /// `currentType` is the current type of the variable that will use the
+  /// constraint, or nullptr if a type is unknown. `allowNonCoreConstraints`
+  /// indicates if user defined constraints are allowed in the completion
+  /// results. `allowInlineTypeConstraints` enables inline type constraints for
+  /// Attr/Value/ValueRange.
+  virtual void codeCompleteConstraintName(ast::Type currentType,
+                                          bool allowNonCoreConstraints,
+                                          bool allowInlineTypeConstraints,
+                                          const ast::DeclScope *scope);
+
+  /// Signal code completion for a dialect name.
+  virtual void codeCompleteDialectName() {}
+
+  /// Signal code completion for an operation name in the given dialect.
+  virtual void codeCompleteOperationName(StringRef dialectName) {}
+
+  /// Signal code completion for Pattern metadata.
+  virtual void codeCompletePatternMetadata() {}
+
+protected:
+  /// Create a new code completion context with the given code complete
+  /// location.
+  explicit CodeCompleteContext(SMLoc codeCompleteLoc)
+      : codeCompleteLoc(codeCompleteLoc) {}
+
+private:
+  /// The location used to code complete.
+  SMLoc codeCompleteLoc;
+};
+} // namespace pdll
+} // namespace mlir
+
+#endif // MLIR_TOOLS_PDLL_PARSER_CODECOMPLETE_H_

mlir/include/mlir/Tools/PDLL/Parser/Parser.h

 #include "mlir/Support/LogicalResult.h"
 
 namespace llvm {
 class SourceMgr;
 } // namespace llvm
 
 namespace mlir {
 namespace pdll {
+class CodeCompleteContext;
+
 namespace ast {
 class Context;
 class Module;
 } // namespace ast
 
-/// Parse an AST module from the main file of the given source manager.
-FailureOr<ast::Module *> parsePDLAST(ast::Context &ctx,
-                                     llvm::SourceMgr &sourceMgr);
+/// Parse an AST module from the main file of the given source manager. An
+/// optional code completion context may be provided to receive code completion
+/// suggestions. If a completion is hit, this method returns a failure.
+FailureOr<ast::Module *>
+parsePDLAST(ast::Context &ctx, llvm::SourceMgr &sourceMgr,
+            CodeCompleteContext *codeCompleteContext = nullptr);
 } // namespace pdll
 } // namespace mlir
 
 #endif // MLIR_TOOLS_PDLL_PARSER_PARSER_H_

mlir/lib/Tools/PDLL/Parser/CMakeLists.txt

 
 llvm_add_library(MLIRPDLLParser STATIC
+  CodeComplete.cpp
   Lexer.cpp
   Parser.cpp
   
   DISABLE_LLVM_LINK_LLVM_DYLIB
 
   LINK_COMPONENTS
   Support
   TableGen
 
   LINK_LIBS PUBLIC
   MLIRPDLLAST
   MLIRSupport
   MLIRTableGen
   )

mlir/lib/Tools/PDLL/Parser/CodeComplete.cpp

+//===- CodeComplete.cpp ---------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "mlir/Tools/PDLL/Parser/CodeComplete.h"
+#include "mlir/Tools/PDLL/AST/Types.h"
+
+using namespace mlir;
+using namespace mlir::pdll;
+
+//===----------------------------------------------------------------------===//
+// CodeCompleteContext
+//===----------------------------------------------------------------------===//
+
+CodeCompleteContext::~CodeCompleteContext() = default;
+
+void CodeCompleteContext::codeCompleteTupleMemberAccess(
+    ast::TupleType tupleType) {}
+void CodeCompleteContext::codeCompleteOperationMemberAccess(
+    ast::OperationType opType) {}
+
+void CodeCompleteContext::codeCompleteConstraintName(
+    ast::Type currentType, bool allowNonCoreConstraints,
+    bool allowInlineTypeConstraints, const ast::DeclScope *scope) {}

mlir/lib/Tools/PDLL/Parser/Lexer.h

 namespace llvm {
 class SourceMgr;
 } // namespace llvm
 
 namespace mlir {
 struct LogicalResult;
 
 namespace pdll {
+class CodeCompleteContext;
+
 namespace ast {
 class DiagnosticEngine;
 } // namespace ast
 
 //===----------------------------------------------------------------------===//
 // Token
 //===----------------------------------------------------------------------===//
 
 class Token {
 public:
   enum Kind {
     // Markers.
     eof,
     error,
+    code_complete,
 
     // Keywords.
     KW_BEGIN,
     // Dependent keywords, i.e. those that are treated as keywords depending on
     // the current parser context.
     KW_DEPENDENT_BEGIN,
     kw_attr,
     kw_op,

 };
 
 //===----------------------------------------------------------------------===//
 // Lexer
 //===----------------------------------------------------------------------===//
 
 class Lexer {
 public:
-  Lexer(llvm::SourceMgr &mgr, ast::DiagnosticEngine &diagEngine);
+  Lexer(llvm::SourceMgr &mgr, ast::DiagnosticEngine &diagEngine,
+        CodeCompleteContext *codeCompleteContext);
   ~Lexer();
 
   /// Return a reference to the source manager used by the lexer.
   llvm::SourceMgr &getSourceMgr() { return srcMgr; }
 
   /// Return a reference to the diagnostic engine used by the lexer.
   ast::DiagnosticEngine &getDiagEngine() { return diagEngine; }
 
private:
   const char *curPtr;
 
   /// The engine used to emit diagnostics during lexing/parsing.
   ast::DiagnosticEngine &diagEngine;
 
   /// A flag indicating if we added a default diagnostic handler to the provided
   /// diagEngine.
   bool addedHandlerToDiagEngine;
+
+  /// The optional code completion point within the input file.
+  const char *codeCompletionLocation;
 };
 } // namespace pdll
 } // namespace mlir
 
 #endif // LIB_TOOLS_PDLL_PARSER_LEXER_H_

mlir/lib/Tools/PDLL/Parser/Lexer.cpp

 //===- Lexer.cpp ----------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "Lexer.h"
 #include "mlir/Support/LogicalResult.h"
 #include "mlir/Tools/PDLL/AST/Diagnostic.h"
+#include "mlir/Tools/PDLL/Parser/CodeComplete.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/StringSwitch.h"
 #include "llvm/Support/SourceMgr.h"
 
 using namespace mlir;
 using namespace mlir::pdll;
 
 //===----------------------------------------------------------------------===//
std::string Token::getStringValue() const {
 
   return result;
 }
 
 //===----------------------------------------------------------------------===//
 // Lexer
 //===----------------------------------------------------------------------===//
 
-Lexer::Lexer(llvm::SourceMgr &mgr, ast::DiagnosticEngine &diagEngine)
-    : srcMgr(mgr), diagEngine(diagEngine), addedHandlerToDiagEngine(false) {
+Lexer::Lexer(llvm::SourceMgr &mgr, ast::DiagnosticEngine &diagEngine,
+             CodeCompleteContext *codeCompleteContext)
+    : srcMgr(mgr), diagEngine(diagEngine), addedHandlerToDiagEngine(false),
+      codeCompletionLocation(nullptr) {
   curBufferID = mgr.getMainFileID();
   curBuffer = srcMgr.getMemoryBuffer(curBufferID)->getBuffer();
   curPtr = curBuffer.begin();
 
+  // Set the code completion location if necessary.
+  if (codeCompleteContext) {
+    codeCompletionLocation =
+        codeCompleteContext->getCodeCompleteLoc().getPointer();
+  }
+
   // If the diag engine has no handler, add a default that emits to the
   // SourceMgr.
   if (!diagEngine.getHandlerFn()) {
     diagEngine.setHandlerFn([&](const ast::Diagnostic &diag) {
       srcMgr.PrintMessage(diag.getLocation().Start, diag.getSeverity(),
                           diag.getMessage());
       for (const ast::Diagnostic &note : diag.getNotes())
         srcMgr.PrintMessage(note.getLocation().Start, note.getSeverity(),
case '\r':
       return '\n';
   }
 }
 
 Token Lexer::lexToken() {
   while (true) {
     const char *tokStart = curPtr;
 
+    // Check to see if this token is at the code completion location.
+    if (tokStart == codeCompletionLocation)
+      return formToken(Token::code_complete, tokStart);
+
     // This always consumes at least one character.
     int curChar = getNextChar();
     switch (curChar) {
       default:
         // Handle identifiers: [a-zA-Z_]
         if (isalpha(curChar) || curChar == '_') return lexIdentifier(tokStart);
 
         // Unknown character, emit an error.

mlir/lib/Tools/PDLL/Parser/Parser.cpp

 #include "mlir/TableGen/Operator.h"
 #include "mlir/Tools/PDLL/AST/Context.h"
 #include "mlir/Tools/PDLL/AST/Diagnostic.h"
 #include "mlir/Tools/PDLL/AST/Nodes.h"
 #include "mlir/Tools/PDLL/AST/Types.h"
 #include "mlir/Tools/PDLL/ODS/Constraint.h"
 #include "mlir/Tools/PDLL/ODS/Context.h"
 #include "mlir/Tools/PDLL/ODS/Operation.h"
+#include "mlir/Tools/PDLL/Parser/CodeComplete.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/TypeSwitch.h"
 #include "llvm/Support/FormatVariadic.h"
 #include "llvm/Support/ManagedStatic.h"
 #include "llvm/Support/SaveAndRestore.h"
 #include "llvm/Support/ScopedPrinter.h"
 #include "llvm/TableGen/Error.h"
 #include "llvm/TableGen/Parser.h"
 #include <string>
 
 using namespace mlir;
 using namespace mlir::pdll;
 
 //===----------------------------------------------------------------------===//
 // Parser
 //===----------------------------------------------------------------------===//
 
 namespace {
 class Parser {
 public:
-  Parser(ast::Context &ctx, llvm::SourceMgr &sourceMgr)
-      : ctx(ctx), lexer(sourceMgr, ctx.getDiagEngine()),
+  Parser(ast::Context &ctx, llvm::SourceMgr &sourceMgr,
+         CodeCompleteContext *codeCompleteContext)
+      : ctx(ctx), lexer(sourceMgr, ctx.getDiagEngine(), codeCompleteContext),
         curToken(lexer.lexToken()), valueTy(ast::ValueType::get(ctx)),
         valueRangeTy(ast::ValueRangeType::get(ctx)),
         typeTy(ast::TypeType::get(ctx)),
         typeRangeTy(ast::TypeRangeType::get(ctx)),
-        attrTy(ast::AttributeType::get(ctx)) {}
+        attrTy(ast::AttributeType::get(ctx)),
+        codeCompleteContext(codeCompleteContext) {}
 
   /// Try to parse a new module. Returns nullptr in the case of failure.
   FailureOr<ast::Module *> parseModule();
 
 private:
   /// The current context of the parser. It allows for the parser to know a bit
   /// about the construct it is nested within during parsing. This is used
   /// specifically to provide additional verification during parsing, e.g. to
private:
 
   /// This structure contains the set of pattern metadata that may be parsed.
   struct ParsedPatternMetadata {
     Optional<uint16_t> benefit;
     bool hasBoundedRecursion = false;
   };
 
   FailureOr<ast::Decl *> parseTopLevelDecl();
-  FailureOr<ast::NamedAttributeDecl *> parseNamedAttributeDecl();
+  FailureOr<ast::NamedAttributeDecl *>
+  parseNamedAttributeDecl(Optional<StringRef> parentOpName);
 
   /// Parse an argument variable as part of the signature of a
   /// UserConstraintDecl or UserRewriteDecl.
   FailureOr<ast::VariableDecl *> parseArgumentDecl();
 
   /// Parse a result variable as part of the signature of a UserConstraintDecl
   /// or UserRewriteDecl.
   FailureOr<ast::VariableDecl *> parseResultDecl(unsigned resultNum);
private:
   FailureOr<ast::Expr *> parseTypeConstraintExpr();
 
   /// Try to parse a single reference to a constraint. `typeConstraint` is the
   /// location of a previously parsed type constraint for the entity that will
   /// be constrained by the parsed constraint. `existingConstraints` are any
   /// existing constraints that have already been parsed for the same entity
   /// that will be constrained by this constraint. `allowInlineTypeConstraints`
   /// allows the use of inline Type constraints, e.g. `Value<valueType: Type>`.
+  /// If `allowNonCoreConstraints` is true, then complex (e.g. user defined
+  /// constraints) may be used with the variable.
   FailureOr<ast::ConstraintRef>
   parseConstraint(Optional<SMRange> &typeConstraint,
                   ArrayRef<ast::ConstraintRef> existingConstraints,
-                  bool allowInlineTypeConstraints);
+                  bool allowInlineTypeConstraints,
+                  bool allowNonCoreConstraints);
 
   /// Try to parse the constraint for a UserConstraintDecl/UserRewriteDecl
   /// argument or result variable. The constraints for these variables do not
   /// allow inline type constraints, and only permit a single constraint.
   FailureOr<ast::ConstraintRef> parseArgOrResultConstraint();
 
   //===--------------------------------------------------------------------===//
   // Exprs
private:
   FailureOr<ast::VariableDecl *>
   createArgOrResultVariableDecl(StringRef name, SMRange loc,
                                 const ast::ConstraintRef &constraint);
 
   /// Validate the constraints used to constraint a variable decl.
   /// `inferredType` is the type of the variable inferred by the constraints
   /// within the list, and is updated to the most refined type as determined by
   /// the constraints. Returns success if the constraint list is valid, failure
-  /// otherwise.
+  /// otherwise. If `allowNonCoreConstraints` is true, then complex (e.g. user
+  /// defined constraints) may be used with the variable.
   LogicalResult
   validateVariableConstraints(ArrayRef<ast::ConstraintRef> constraints,
-                              ast::Type &inferredType);
+                              ast::Type &inferredType,
+                              bool allowNonCoreConstraints = true);
   /// Validate a single reference to a constraint. `inferredType` contains the
   /// currently inferred variabled type and is refined within the type defined
   /// by the constraint. Returns success if the constraint is valid, failure
   /// otherwise. If `allowNonCoreConstraints` is true, then complex (e.g. user
   /// defined constraints) may be used with the variable.
   LogicalResult validateVariableConstraint(const ast::ConstraintRef &ref,
                                            ast::Type &inferredType,
                                            bool allowNonCoreConstraints = true);
private:
   FailureOr<ast::ReplaceStmt *>
   createReplaceStmt(SMRange loc, ast::Expr *rootOp,
                     MutableArrayRef<ast::Expr *> replValues);
   FailureOr<ast::RewriteStmt *>
   createRewriteStmt(SMRange loc, ast::Expr *rootOp,
                     ast::CompoundStmt *rewriteBody);
 
   //===--------------------------------------------------------------------===//
+  // Code Completion
+  //===--------------------------------------------------------------------===//
+
+  /// The set of various code completion methods. Every completion method
+  /// returns `failure` to stop the parsing process after providing completion
+  /// results.
+
+  LogicalResult codeCompleteMemberAccess(ast::Expr *parentExpr);
+  LogicalResult codeCompleteAttributeName(Optional<StringRef> opName);
+  LogicalResult codeCompleteConstraintName(ast::Type inferredType,
+                                           bool allowNonCoreConstraints,
+                                           bool allowInlineTypeConstraints);
+  LogicalResult codeCompleteDialectName();
+  LogicalResult codeCompleteOperationName(StringRef dialectName);
+  LogicalResult codeCompletePatternMetadata();
+
+  //===--------------------------------------------------------------------===//
   // Lexer Utilities
   //===--------------------------------------------------------------------===//
 
   /// If the current token has the specified kind, consume it and return true.
   /// If not, return false.
   bool consumeIf(Token::Kind kind) {
     if (curToken.isNot(kind))
       return false;
private:
 
   /// Cached types to simplify verification and expression creation.
   ast::Type valueTy, valueRangeTy;
   ast::Type typeTy, typeRangeTy;
   ast::Type attrTy;
 
   /// A counter used when naming anonymous constraints and rewrites.
   unsigned anonymousDeclNameCounter = 0;
+
+  /// The optional code completion context.
+  CodeCompleteContext *codeCompleteContext;
 };
 } // namespace
 
 FailureOr<ast::Module *> Parser::parseModule() {
   SMLoc moduleLoc = curToken.getStartLoc();
   pushDeclScope();
 
   // Parse the top-level decls of the module.
FailureOr<ast::Decl *> Parser::parseTopLevelDecl() {
   if (const ast::Name *name = (*decl)->getName()) {
     if (failed(checkDefineNamedDecl(*name)))
       return failure();
     curDeclScope->add(*decl);
   }
   return decl;
 }
 
-FailureOr<ast::NamedAttributeDecl *> Parser::parseNamedAttributeDecl() {
+FailureOr<ast::NamedAttributeDecl *>
+Parser::parseNamedAttributeDecl(Optional<StringRef> parentOpName) {
+  // Check for name code completion.
+  if (curToken.is(Token::code_complete))
+    return codeCompleteAttributeName(parentOpName);
+
   std::string attrNameStr;
   if (curToken.isString())
     attrNameStr = curToken.getStringValue();
   else if (curToken.is(Token::identifier) || curToken.isKeyword())
     attrNameStr = curToken.getSpelling().str();
   else
     return emitError("expected identifier or string attribute name");
   const auto &name = ast::Name::create(ctx, attrNameStr, curToken.getLoc());

 }
 
 LogicalResult
 Parser::parsePatternDeclMetadata(ParsedPatternMetadata &metadata) {
   Optional<SMRange> benefitLoc;
   Optional<SMRange> hasBoundedRecursionLoc;
 
   do {
+    // Handle metadata code completion.
+    if (curToken.is(Token::code_complete))
+      return codeCompletePatternMetadata();
+
     if (curToken.isNot(Token::identifier))
       return emitError("expected pattern metadata identifier");
     StringRef metadataStr = curToken.getSpelling();
     SMRange metadataLoc = curToken.getLoc();
     consumeToken(Token::identifier);
 
     // Parse the benefit metadata: benefit(<integer-value>)
     if (metadataStr == "benefit") {
return defineVariableDecl(name, nameLoc, type, /*initExpr=*/nullptr,
                             constraints);
 }
 
 LogicalResult Parser::parseVariableDeclConstraintList(
     SmallVectorImpl<ast::ConstraintRef> &constraints) {
   Optional<SMRange> typeConstraint;
   auto parseSingleConstraint = [&] {
     FailureOr<ast::ConstraintRef> constraint = parseConstraint(
-        typeConstraint, constraints, /*allowInlineTypeConstraints=*/true);
+        typeConstraint, constraints, /*allowInlineTypeConstraints=*/true,
+        /*allowNonCoreConstraints=*/true);
     if (failed(constraint))
       return failure();
     constraints.push_back(*constraint);
     return success();
   };
 
   // Check to see if this is a single constraint, or a list.
   if (!consumeIf(Token::l_square))
     return parseSingleConstraint();
 
   do {
     if (failed(parseSingleConstraint()))
       return failure();
   } while (consumeIf(Token::comma));
   return parseToken(Token::r_square, "expected `]` after constraint list");
 }
 
 FailureOr<ast::ConstraintRef>
 Parser::parseConstraint(Optional<SMRange> &typeConstraint,
                         ArrayRef<ast::ConstraintRef> existingConstraints,
-                        bool allowInlineTypeConstraints) {
+                        bool allowInlineTypeConstraints,
+                        bool allowNonCoreConstraints) {
   auto parseTypeConstraint = [&](ast::Expr *&typeExpr) -> LogicalResult {
     if (!allowInlineTypeConstraints) {
       return emitError(
           curToken.getLoc(),
           "inline `Attr`, `Value`, and `ValueRange` type constraints are not "
           "permitted on arguments or results");
     }
     if (typeConstraint)
case Token::identifier: {
     // Handle a reference to a proper constraint.
     if (auto *cst = dyn_cast<ast::ConstraintDecl>(cstDecl))
       return ast::ConstraintRef(cst, loc);
 
     return emitErrorAndNote(
         loc, "invalid reference to non-constraint", cstDecl->getLoc(),
         "see the definition of `" + constraintName + "` here");
   }
+    // Handle single entity constraint code completion.
+  case Token::code_complete: {
+    // Try to infer the current type for use by code completion.
+    ast::Type inferredType;
+    if (failed(validateVariableConstraints(existingConstraints, inferredType,
+                                           allowNonCoreConstraints)))
+      return failure();
+
+    return codeCompleteConstraintName(inferredType, allowNonCoreConstraints,
+                                      allowInlineTypeConstraints);
+  }
   default:
     break;
   }
   return emitError(loc, "expected identifier constraint");
 }
 
 FailureOr<ast::ConstraintRef> Parser::parseArgOrResultConstraint() {
+  // Constraint arguments may apply more complex constraints via the arguments.
+  bool allowNonCoreConstraints = parserContext == ParserContext::Constraint;
+
   Optional<SMRange> typeConstraint;
   return parseConstraint(typeConstraint, /*existingConstraints=*/llvm::None,
-                         /*allowInlineTypeConstraints=*/false);
+                         /*allowInlineTypeConstraints=*/false,
+                         allowNonCoreConstraints);
 }
 
 //===----------------------------------------------------------------------===//
 // Exprs
 
 FailureOr<ast::Expr *> Parser::parseExpr() {
   if (curToken.is(Token::underscore))
     return parseUnderscoreExpr();
FailureOr<ast::Expr *> Parser::parseInlineRewriteLambdaExpr() {
   return ast::DeclRefExpr::create(ctx, (*decl)->getLoc(), *decl,
                                   ast::RewriteType::get(ctx));
 }
 
 FailureOr<ast::Expr *> Parser::parseMemberAccessExpr(ast::Expr *parentExpr) {
   SMRange loc = curToken.getLoc();
   consumeToken(Token::dot);
 
+  // Check for code completion of the member name.
+  if (curToken.is(Token::code_complete))
+    return codeCompleteMemberAccess(parentExpr);
+
   // Parse the member name.
   Token memberNameTok = curToken;
   if (memberNameTok.isNot(Token::identifier, Token::integer) &&
       !memberNameTok.isKeyword())
     return emitError(loc, "expected identifier or numeric member name");
   StringRef memberName = memberNameTok.getSpelling();
   consumeToken();
 
   return createMemberAccessExpr(parentExpr, memberName, loc);
 }
 
 FailureOr<ast::OpNameDecl *> Parser::parseOperationName(bool allowEmptyName) {
   SMRange loc = curToken.getLoc();
 
+  // Check for code completion for the dialect name.
+  if (curToken.is(Token::code_complete))
+    return codeCompleteDialectName();
+
   // Handle the case of an no operation name.
   if (curToken.isNot(Token::identifier) && !curToken.isKeyword()) {
     if (allowEmptyName)
       return ast::OpNameDecl::create(ctx, SMRange());
     return emitError("expected dialect namespace");
   }
   StringRef name = curToken.getSpelling();
   consumeToken();
 
   // Otherwise, this is a literal operation name.
   if (failed(parseToken(Token::dot, "expected `.` after dialect namespace")))
     return failure();
 
+  // Check for code completion for the operation name.
+  if (curToken.is(Token::code_complete))
+    return codeCompleteOperationName(name);
+
   if (curToken.isNot(Token::identifier) && !curToken.isKeyword())
     return emitError("expected operation name after dialect namespace");
 
   name = StringRef(name.data(), name.size() + 1);
   do {
     name = StringRef(name.data(), name.size() + curToken.getSpelling().size());
     loc.End = curToken.getEndLoc();
     consumeToken();
FailureOr<ast::Expr *> Parser::parseOperationExpr() {
   // Parse the operation name. The name may be elided, in which case the
   // operation refers to "any" operation(i.e. a difference between `MyOp` and
   // `Operation*`). Operation names within a rewrite context must be named.
   bool allowEmptyName = parserContext != ParserContext::Rewrite;
   FailureOr<ast::OpNameDecl *> opNameDecl =
       parseWrappedOperationName(allowEmptyName);
   if (failed(opNameDecl))
     return failure();
+  Optional<StringRef> opName = (*opNameDecl)->getName();
 
   // Functor used to create an implicit range variable, used for implicit "all"
   // operand or results variables.
   auto createImplicitRangeVar = [&](ast::ConstraintDecl *cst, ast::Type type) {
     FailureOr<ast::VariableDecl *> rangeVar =
         defineVariableDecl("_", loc, type, ast::ConstraintRef(cst, loc));
     assert(succeeded(rangeVar) && "expected range variable to be valid");
     return ast::DeclRefExpr::create(ctx, loc, *rangeVar, type);
if (failed(parseToken(Token::r_paren,
                           "expected `)` after operation operand list")))
       return failure();
   }
 
   // Check for the optional list of attributes.
   SmallVector<ast::NamedAttributeDecl *> attributes;
   if (consumeIf(Token::l_brace)) {
     do {
-      FailureOr<ast::NamedAttributeDecl *> decl = parseNamedAttributeDecl();
+      FailureOr<ast::NamedAttributeDecl *> decl =
+          parseNamedAttributeDecl(opName);
       if (failed(decl))
         return failure();
       attributes.emplace_back(*decl);
     } while (consumeIf(Token::comma));
 
     if (failed(parseToken(Token::r_brace,
                           "expected `}` after operation attribute list")))
       return failure();
Parser::createArgOrResultVariableDecl(StringRef name, SMRange loc,
   if (failed(validateVariableConstraint(constraint, argType,
                                         allowNonCoreConstraints)))
     return failure();
   return defineVariableDecl(name, loc, argType, constraint);
 }
 
 LogicalResult
 Parser::validateVariableConstraints(ArrayRef<ast::ConstraintRef> constraints,
-                                    ast::Type &inferredType) {
+                                    ast::Type &inferredType,
+                                    bool allowNonCoreConstraints) {
   for (const ast::ConstraintRef &ref : constraints)
-    if (failed(validateVariableConstraint(ref, inferredType)))
+    if (failed(validateVariableConstraint(ref, inferredType,
+                                          allowNonCoreConstraints)))
       return failure();
   return success();
 }
 
 LogicalResult Parser::validateVariableConstraint(const ast::ConstraintRef &ref,
                                                  ast::Type &inferredType,
                                                  bool allowNonCoreConstraints) {
   ast::Type constraintType;
return emitError(
         rootOp->getLoc(),
         llvm::formatv("expected `Op` expression, but got `{0}`", rootType));
   }
 
   return ast::RewriteStmt::create(ctx, loc, rootOp, rewriteBody);
 }
 
 //===----------------------------------------------------------------------===//
+// Code Completion
+//===----------------------------------------------------------------------===//
+
+LogicalResult Parser::codeCompleteMemberAccess(ast::Expr *parentExpr) {
+  ast::Type parentType = parentExpr->getType();
+  if (ast::OperationType opType = parentType.dyn_cast<ast::OperationType>())
+    codeCompleteContext->codeCompleteOperationMemberAccess(opType);
+  else if (ast::TupleType tupleType = parentType.dyn_cast<ast::TupleType>())
+    codeCompleteContext->codeCompleteTupleMemberAccess(tupleType);
+  return failure();
+}
+
+LogicalResult Parser::codeCompleteAttributeName(Optional<StringRef> opName) {
+  if (opName)
+    codeCompleteContext->codeCompleteOperationAttributeName(*opName);
+  return failure();
+}
+
+LogicalResult
+Parser::codeCompleteConstraintName(ast::Type inferredType,
+                                   bool allowNonCoreConstraints,
+                                   bool allowInlineTypeConstraints) {
+  codeCompleteContext->codeCompleteConstraintName(
+      inferredType, allowNonCoreConstraints, allowInlineTypeConstraints,
+      curDeclScope);
+  return failure();
+}
+
+LogicalResult Parser::codeCompleteDialectName() {
+  codeCompleteContext->codeCompleteDialectName();
+  return failure();
+}
+
+LogicalResult Parser::codeCompleteOperationName(StringRef dialectName) {
+  codeCompleteContext->codeCompleteOperationName(dialectName);
+  return failure();
+}
+
+LogicalResult Parser::codeCompletePatternMetadata() {
+  codeCompleteContext->codeCompletePatternMetadata();
+  return failure();
+}
+
+//===----------------------------------------------------------------------===//
 // Parser
 //===----------------------------------------------------------------------===//
 
-FailureOr<ast::Module *> mlir::pdll::parsePDLAST(ast::Context &ctx,
-                                                 llvm::SourceMgr &sourceMgr) {
-  Parser parser(ctx, sourceMgr);
+FailureOr<ast::Module *>
+mlir::pdll::parsePDLAST(ast::Context &ctx, llvm::SourceMgr &sourceMgr,
+                        CodeCompleteContext *codeCompleteContext) {
+  Parser parser(ctx, sourceMgr, codeCompleteContext);
   return parser.parseModule();
 }

mlir/lib/Tools/lsp-server-support/Protocol.h

 //===--- Protocol.h - Language Server Protocol Implementation ---*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
 // This file contains structs based on the LSP specification at
-// https://github.com/Microsoft/language-server-protocol/blob/main/protocol.md
+// https://microsoft.github.io/language-server-protocol/specification
 //
 // This is not meant to be a complete implementation, new interfaces are added
 // when they're needed.
 //
 // Each struct has a toJSON and fromJSON function, that converts between
 // the struct and a JSON representation. (See JSON.h)
 //
 // Some structs also have operator<< serialization. This is for debugging and
struct PublishDiagnosticsParams {
   std::vector<Diagnostic> diagnostics;
   /// The version number of the document the diagnostics are published for.
   int64_t version;
 };
 
 /// Add support for JSON serialization.
 llvm::json::Value toJSON(const PublishDiagnosticsParams &params);
 
+//===----------------------------------------------------------------------===//
+// TextEdit
+//===----------------------------------------------------------------------===//
+
+struct TextEdit {
+  /// The range of the text document to be manipulated. To insert
+  /// text into a document create a range where start === end.
+  Range range;
+
+  /// The string to be inserted. For delete operations use an
+  /// empty string.
+  std::string newText;
+};
+
+inline bool operator==(const TextEdit &lhs, const TextEdit &rhs) {
+  return std::tie(lhs.newText, lhs.range) == std::tie(rhs.newText, rhs.range);
+}
+
+bool fromJSON(const llvm::json::Value &value, TextEdit &result,
+              llvm::json::Path path);
+llvm::json::Value toJSON(const TextEdit &value);
+raw_ostream &operator<<(raw_ostream &os, const TextEdit &value);
+
+//===----------------------------------------------------------------------===//
+// CompletionItemKind
+//===----------------------------------------------------------------------===//
+
+/// The kind of a completion entry.
+enum class CompletionItemKind {
+  Missing = 0,
+  Text = 1,
+  Method = 2,
+  Function = 3,
+  Constructor = 4,
+  Field = 5,
+  Variable = 6,
+  Class = 7,
+  Interface = 8,
+  Module = 9,
+  Property = 10,
+  Unit = 11,
+  Value = 12,
+  Enum = 13,
+  Keyword = 14,
+  Snippet = 15,
+  Color = 16,
+  File = 17,
+  Reference = 18,
+  Folder = 19,
+  EnumMember = 20,
+  Constant = 21,
+  Struct = 22,
+  Event = 23,
+  Operator = 24,
+  TypeParameter = 25,
+};
+bool fromJSON(const llvm::json::Value &value, CompletionItemKind &result,
+              llvm::json::Path path);
+
+constexpr auto kCompletionItemKindMin =
+    static_cast<size_t>(CompletionItemKind::Text);
+constexpr auto kCompletionItemKindMax =
+    static_cast<size_t>(CompletionItemKind::TypeParameter);
+using CompletionItemKindBitset = std::bitset<kCompletionItemKindMax + 1>;
+bool fromJSON(const llvm::json::Value &value, CompletionItemKindBitset &result,
+              llvm::json::Path path);
+
+CompletionItemKind
+adjustKindToCapability(CompletionItemKind kind,
+                       CompletionItemKindBitset &supportedCompletionItemKinds);
+
+//===----------------------------------------------------------------------===//
+// CompletionItem
+//===----------------------------------------------------------------------===//
+
+/// Defines whether the insert text in a completion item should be interpreted
+/// as plain text or a snippet.
+enum class InsertTextFormat {
+  Missing = 0,
+  /// The primary text to be inserted is treated as a plain string.
+  PlainText = 1,
+  /// The primary text to be inserted is treated as a snippet.
+  ///
+  /// A snippet can define tab stops and placeholders with `$1`, `$2`
+  /// and `${3:foo}`. `$0` defines the final tab stop, it defaults to the end
+  /// of the snippet. Placeholders with equal identifiers are linked, that is
+  /// typing in one will update others too.
+  ///
+  /// See also:
+  /// https//github.com/Microsoft/vscode/blob/master/src/vs/editor/contrib/snippet/common/snippet.md
+  Snippet = 2,
+};
+
+struct CompletionItem {
+  /// The label of this completion item. By default also the text that is
+  /// inserted when selecting this completion.
+  std::string label;
+
+  /// The kind of this completion item. Based of the kind an icon is chosen by
+  /// the editor.
+  CompletionItemKind kind = CompletionItemKind::Missing;
+
+  /// A human-readable string with additional information about this item, like
+  /// type or symbol information.
+  std::string detail;
+
+  /// A human-readable string that represents a doc-comment.
+  Optional<MarkupContent> documentation;
+
+  /// A string that should be used when comparing this item with other items.
+  /// When `falsy` the label is used.
+  std::string sortText;
+
+  /// A string that should be used when filtering a set of completion items.
+  /// When `falsy` the label is used.
+  std::string filterText;
+
+  /// A string that should be inserted to a document when selecting this
+  /// completion. When `falsy` the label is used.
+  std::string insertText;
+
+  /// The format of the insert text. The format applies to both the `insertText`
+  /// property and the `newText` property of a provided `textEdit`.
+  InsertTextFormat insertTextFormat = InsertTextFormat::Missing;
+
+  /// An edit which is applied to a document when selecting this completion.
+  /// When an edit is provided `insertText` is ignored.
+  ///
+  /// Note: The range of the edit must be a single line range and it must
+  /// contain the position at which completion has been requested.
+  Optional<TextEdit> textEdit;
+
+  /// An optional array of additional text edits that are applied when selecting
+  /// this completion. Edits must not overlap with the main edit nor with
+  /// themselves.
+  std::vector<TextEdit> additionalTextEdits;
+
+  /// Indicates if this item is deprecated.
+  bool deprecated = false;
+};
+
+/// Add support for JSON serialization.
+llvm::json::Value toJSON(const CompletionItem &value);
+raw_ostream &operator<<(raw_ostream &os, const CompletionItem &value);
+bool operator<(const CompletionItem &lhs, const CompletionItem &rhs);
+
+//===----------------------------------------------------------------------===//
+// CompletionList
+//===----------------------------------------------------------------------===//
+
+/// Represents a collection of completion items to be presented in the editor.
+struct CompletionList {
+  /// The list is not complete. Further typing should result in recomputing the
+  /// list.
+  bool isIncomplete = false;
+
+  /// The completion items.
+  std::vector<CompletionItem> items;
+};
+
+/// Add support for JSON serialization.
+llvm::json::Value toJSON(const CompletionList &value);
+
+//===----------------------------------------------------------------------===//
+// CompletionContext
+//===----------------------------------------------------------------------===//
+
+enum class CompletionTriggerKind {
+  /// Completion was triggered by typing an identifier (24x7 code
+  /// complete), manual invocation (e.g Ctrl+Space) or via API.
+  Invoked = 1,
+
+  /// Completion was triggered by a trigger character specified by
+  /// the `triggerCharacters` properties of the `CompletionRegistrationOptions`.
+  TriggerCharacter = 2,
+
+  /// Completion was re-triggered as the current completion list is incomplete.
+  TriggerTriggerForIncompleteCompletions = 3
+};
+
+struct CompletionContext {
+  /// How the completion was triggered.
+  CompletionTriggerKind triggerKind = CompletionTriggerKind::Invoked;
+
+  /// The trigger character (a single character) that has trigger code complete.
+  /// Is undefined if `triggerKind !== CompletionTriggerKind.TriggerCharacter`
+  std::string triggerCharacter;
+};
+
+/// Add support for JSON serialization.
+bool fromJSON(const llvm::json::Value &value, CompletionContext &result,
+              llvm::json::Path path);
+
+//===----------------------------------------------------------------------===//
+// CompletionParams
+//===----------------------------------------------------------------------===//
+
+struct CompletionParams : TextDocumentPositionParams {
+  CompletionContext context;
+};
+
+/// Add support for JSON serialization.
+bool fromJSON(const llvm::json::Value &value, CompletionParams &result,
+              llvm::json::Path path);
+
 } // namespace lsp
 } // namespace mlir
 
 namespace llvm {
 template <>
 struct format_provider<mlir::lsp::Position> {
   static void format(const mlir::lsp::Position &pos, raw_ostream &os,
                      StringRef style) {
     assert(style.empty() && "style modifiers for this type are not supported");
     os << pos;
   }
 };
 } // namespace llvm
 
 #endif

mlir/lib/Tools/lsp-server-support/Protocol.cpp

 
 llvm::json::Value mlir::lsp::toJSON(const PublishDiagnosticsParams &params) {
   return llvm::json::Object{
       {"uri", params.uri},
       {"diagnostics", params.diagnostics},
       {"version", params.version},
   };
 }
+
+//===----------------------------------------------------------------------===//
+// TextEdit
+//===----------------------------------------------------------------------===//
+
+bool mlir::lsp::fromJSON(const llvm::json::Value &value, TextEdit &result,
+                         llvm::json::Path path) {
+  llvm::json::ObjectMapper o(value, path);
+  return o && o.map("range", result.range) && o.map("newText", result.newText);
+}
+
+llvm::json::Value mlir::lsp::toJSON(const TextEdit &value) {
+  return llvm::json::Object{
+      {"range", value.range},
+      {"newText", value.newText},
+  };
+}
+
+raw_ostream &mlir::lsp::operator<<(raw_ostream &os, const TextEdit &value) {
+  os << value.range << " => \"";
+  llvm::printEscapedString(value.newText, os);
+  return os << '"';
+}
+
+//===----------------------------------------------------------------------===//
+// CompletionItemKind
+//===----------------------------------------------------------------------===//
+
+bool mlir::lsp::fromJSON(const llvm::json::Value &value,
+                         CompletionItemKind &result, llvm::json::Path path) {
+  if (Optional<int64_t> intValue = value.getAsInteger()) {
+    if (*intValue < static_cast<int>(CompletionItemKind::Text) ||
+        *intValue > static_cast<int>(CompletionItemKind::TypeParameter))
+      return false;
+    result = static_cast<CompletionItemKind>(*intValue);
+    return true;
+  }
+  return false;
+}
+
+CompletionItemKind mlir::lsp::adjustKindToCapability(
+    CompletionItemKind kind,
+    CompletionItemKindBitset &supportedCompletionItemKinds) {
+  size_t kindVal = static_cast<size_t>(kind);
+  if (kindVal >= kCompletionItemKindMin &&
+      kindVal <= supportedCompletionItemKinds.size() &&
+      supportedCompletionItemKinds[kindVal])
+    return kind;
+
+  // Provide some fall backs for common kinds that are close enough.
+  switch (kind) {
+  case CompletionItemKind::Folder:
+    return CompletionItemKind::File;
+  case CompletionItemKind::EnumMember:
+    return CompletionItemKind::Enum;
+  case CompletionItemKind::Struct:
+    return CompletionItemKind::Class;
+  default:
+    return CompletionItemKind::Text;
+  }
+}
+
+bool mlir::lsp::fromJSON(const llvm::json::Value &value,
+                         CompletionItemKindBitset &result,
+                         llvm::json::Path path) {
+  if (const llvm::json::Array *arrayValue = value.getAsArray()) {
+    for (size_t i = 0, e = arrayValue->size(); i < e; ++i) {
+      CompletionItemKind kindOut;
+      if (fromJSON((*arrayValue)[i], kindOut, path.index(i)))
+        result.set(size_t(kindOut));
+    }
+    return true;
+  }
+  return false;
+}
+
+//===----------------------------------------------------------------------===//
+// CompletionItem
+//===----------------------------------------------------------------------===//
+
+llvm::json::Value mlir::lsp::toJSON(const CompletionItem &value) {
+  assert(!value.label.empty() && "completion item label is required");
+  llvm::json::Object result{{"label", value.label}};
+  if (value.kind != CompletionItemKind::Missing)
+    result["kind"] = static_cast<int>(value.kind);
+  if (!value.detail.empty())
+    result["detail"] = value.detail;
+  if (value.documentation)
+    result["documentation"] = value.documentation;
+  if (!value.sortText.empty())
+    result["sortText"] = value.sortText;
+  if (!value.filterText.empty())
+    result["filterText"] = value.filterText;
+  if (!value.insertText.empty())
+    result["insertText"] = value.insertText;
+  if (value.insertTextFormat != InsertTextFormat::Missing)
+    result["insertTextFormat"] = static_cast<int>(value.insertTextFormat);
+  if (value.textEdit)
+    result["textEdit"] = *value.textEdit;
+  if (!value.additionalTextEdits.empty()) {
+    result["additionalTextEdits"] =
+        llvm::json::Array(value.additionalTextEdits);
+  }
+  if (value.deprecated)
+    result["deprecated"] = value.deprecated;
+  return std::move(result);
+}
+
+raw_ostream &mlir::lsp::operator<<(raw_ostream &os,
+                                   const CompletionItem &value) {
+  return os << value.label << " - " << toJSON(value);
+}
+
+bool mlir::lsp::operator<(const CompletionItem &lhs,
+                          const CompletionItem &rhs) {
+  return (lhs.sortText.empty() ? lhs.label : lhs.sortText) <
+         (rhs.sortText.empty() ? rhs.label : rhs.sortText);
+}
+
+//===----------------------------------------------------------------------===//
+// CompletionList
+//===----------------------------------------------------------------------===//
+
+llvm::json::Value mlir::lsp::toJSON(const CompletionList &value) {
+  return llvm::json::Object{
+      {"isIncomplete", value.isIncomplete},
+      {"items", llvm::json::Array(value.items)},
+  };
+}
+
+//===----------------------------------------------------------------------===//
+// CompletionContext
+//===----------------------------------------------------------------------===//
+
+bool mlir::lsp::fromJSON(const llvm::json::Value &value,
+                         CompletionContext &result, llvm::json::Path path) {
+  llvm::json::ObjectMapper o(value, path);
+  int triggerKind;
+  if (!o || !o.map("triggerKind", triggerKind) ||
+      !mapOptOrNull(value, "triggerCharacter", result.triggerCharacter, path))
+    return false;
+  result.triggerKind = static_cast<CompletionTriggerKind>(triggerKind);
+  return true;
+}
+
+//===----------------------------------------------------------------------===//
+// CompletionParams
+//===----------------------------------------------------------------------===//
+
+bool mlir::lsp::fromJSON(const llvm::json::Value &value,
+                         CompletionParams &result, llvm::json::Path path) {
+  if (!fromJSON(value, static_cast<TextDocumentPositionParams &>(result), path))
+    return false;
+  if (const llvm::json::Value *context = value.getAsObject()->get("context"))
+    return fromJSON(*context, result.context, path.field("context"));
+  return true;
+}

mlir/lib/Tools/mlir-pdll-lsp-server/LSPServer.cpp

struct LSPServer {
 
   //===--------------------------------------------------------------------===//
   // Document Symbols
 
   void onDocumentSymbol(const DocumentSymbolParams &params,
                         Callback<std::vector<DocumentSymbol>> reply);
 
   //===--------------------------------------------------------------------===//
+  // Code Completion
+
+  void onCompletion(const CompletionParams &params,
+                    Callback<CompletionList> reply);
+
+  //===--------------------------------------------------------------------===//
   // Fields
   //===--------------------------------------------------------------------===//
 
   PDLLServer &server;
   JSONTransport &transport;
 
   /// An outgoing notification used to send diagnostics to the client when they
   /// are ready to be processed.
void LSPServer::onInitialize(const InitializeParams &params,
   // Send a response with the capabilities of this server.
   llvm::json::Object serverCaps{
       {"textDocumentSync",
        llvm::json::Object{
            {"openClose", true},
            {"change", (int)TextDocumentSyncKind::Full},
            {"save", true},
        }},
+      {"completionProvider",
+       llvm::json::Object{
+           {"allCommitCharacters",
+            {" ", "\t", "(", ")", "[", "]", "{",  "}", "<",
+             ">", ":",  ";", ",", "+", "-", "/",  "*", "%",
+             "^", "&",  "#", "?", ".", "=", "\"", "'", "|"}},
+           {"resolveProvider", false},
+           {"triggerCharacters", {".", ">", "(", "{", ",", "<", ":", "[", " "}},
+       }},
       {"definitionProvider", true},
       {"referencesProvider", true},
       {"hoverProvider", true},
       {"documentSymbolProvider", true},
   };
 
   llvm::json::Object result{
       {{"serverInfo", llvm::json::Object{{"name", "mlir-pdll-lsp-server"},

 void LSPServer::onDocumentSymbol(const DocumentSymbolParams &params,
                                  Callback<std::vector<DocumentSymbol>> reply) {
   std::vector<DocumentSymbol> symbols;
   server.findDocumentSymbols(params.textDocument.uri, symbols);
   reply(std::move(symbols));
 }
 
 //===----------------------------------------------------------------------===//
+// Code Completion
+
+void LSPServer::onCompletion(const CompletionParams &params,
+                             Callback<CompletionList> reply) {
+  reply(server.getCodeCompletion(params.textDocument.uri, params.position));
+}
+
+//===----------------------------------------------------------------------===//
 // Entry Point
 //===----------------------------------------------------------------------===//
 
 LogicalResult mlir::lsp::runPdllLSPServer(PDLLServer &server,
                                           JSONTransport &transport) {
   LSPServer lspServer(server, transport);
   MessageHandler messageHandler(transport);
 
LogicalResult mlir::lsp::runPdllLSPServer(PDLLServer &server,
 
   // Hover
   messageHandler.method("textDocument/hover", &lspServer, &LSPServer::onHover);
 
   // Document Symbols
   messageHandler.method("textDocument/documentSymbol", &lspServer,
                         &LSPServer::onDocumentSymbol);
 
+  // Code Completion
+  messageHandler.method("textDocument/completion", &lspServer,
+                        &LSPServer::onCompletion);
+
   // Diagnostics
   lspServer.publishDiagnostics =
       messageHandler.outgoingNotification<PublishDiagnosticsParams>(
           "textDocument/publishDiagnostics");
 
   // Run the main loop of the transport.
   if (llvm::Error error = transport.run(messageHandler)) {
     Logger::error("Transport error: {0}", error);
     llvm::consumeError(std::move(error));
     return failure();
   }
   return success(lspServer.shutdownRequestReceived);
 }

mlir/lib/Tools/mlir-pdll-lsp-server/PDLLServer.h

 #define LIB_MLIR_TOOLS_MLIRPDLLSPSERVER_SERVER_H_
 
 #include "mlir/Support/LLVM.h"
 #include <memory>
 
 namespace mlir {
 namespace lsp {
 struct Diagnostic;
+struct CompletionList;
 struct DocumentSymbol;
 struct Hover;
 struct Location;
 struct Position;
 class URIForFile;
 
 /// This class implements all of the PDLL related functionality necessary for a
 /// language server. This class allows for keeping the PDLL specific logic
public:
   /// Find a hover description for the given hover position, or None if one
   /// couldn't be found.
   Optional<Hover> findHover(const URIForFile &uri, const Position &hoverPos);
 
   /// Find all of the document symbols within the given file.
   void findDocumentSymbols(const URIForFile &uri,
                            std::vector<DocumentSymbol> &symbols);
 
+  /// Get the code completion list for the position within the given file.
+  CompletionList getCodeCompletion(const URIForFile &uri,
+                                   const Position &completePos);
+
 private:
   struct Impl;
 
   std::unique_ptr<Impl> impl;
 };
 
 } // namespace lsp
 } // namespace mlir
 
 #endif // LIB_MLIR_TOOLS_MLIRPDLLSPSERVER_SERVER_H_

mlir/lib/Tools/mlir-pdll-lsp-server/PDLLServer.cpp

 #include "../lsp-server-support/Protocol.h"
 #include "mlir/Tools/PDLL/AST/Context.h"
 #include "mlir/Tools/PDLL/AST/Nodes.h"
 #include "mlir/Tools/PDLL/AST/Types.h"
 #include "mlir/Tools/PDLL/ODS/Constraint.h"
 #include "mlir/Tools/PDLL/ODS/Context.h"
 #include "mlir/Tools/PDLL/ODS/Dialect.h"
 #include "mlir/Tools/PDLL/ODS/Operation.h"
+#include "mlir/Tools/PDLL/Parser/CodeComplete.h"
 #include "mlir/Tools/PDLL/Parser/Parser.h"
 #include "llvm/ADT/IntervalMap.h"
 #include "llvm/ADT/StringMap.h"
 #include "llvm/ADT/TypeSwitch.h"
 #include "llvm/Support/Path.h"
 
 using namespace mlir;
 using namespace mlir::pdll;
struct PDLDocument {
 
   //===--------------------------------------------------------------------===//
   // Document Symbols
   //===--------------------------------------------------------------------===//
 
   void findDocumentSymbols(std::vector<lsp::DocumentSymbol> &symbols);
 
   //===--------------------------------------------------------------------===//
+  // Code Completion
+  //===--------------------------------------------------------------------===//
+
+  lsp::CompletionList getCodeCompletion(const lsp::URIForFile &uri,
+                                        const lsp::Position &completePos);
+
+  //===--------------------------------------------------------------------===//
   // Fields
   //===--------------------------------------------------------------------===//
 
   /// The include directories for this file.
   std::vector<std::string> includeDirs;
 
   /// The source manager containing the contents of the input file.
   llvm::SourceMgr sourceMgr;
if (const auto *patternDecl = dyn_cast<ast::PatternDecl>(decl)) {
       symbols.emplace_back(
           cDecl->getName().getName(), lsp::SymbolKind::Function,
           lsp::Range(sourceMgr, bodyLoc), lsp::Range(sourceMgr, nameLoc));
     }
   }
 }
 
 //===----------------------------------------------------------------------===//
+// PDLDocument: Code Completion
+//===----------------------------------------------------------------------===//
+
+namespace {
+class LSPCodeCompleteContext : public CodeCompleteContext {
+public:
+  LSPCodeCompleteContext(SMLoc completeLoc, lsp::CompletionList &completionList,
+                         ods::Context &odsContext)
+      : CodeCompleteContext(completeLoc), completionList(completionList),
+        odsContext(odsContext) {}
+
+  void codeCompleteTupleMemberAccess(ast::TupleType tupleType) final {
+    ArrayRef<ast::Type> elementTypes = tupleType.getElementTypes();
+    ArrayRef<StringRef> elementNames = tupleType.getElementNames();
+    for (unsigned i = 0, e = tupleType.size(); i < e; ++i) {
+      // Push back a completion item that uses the result index.
+      lsp::CompletionItem item;
+      item.label = llvm::formatv("{0} (field #{0})", i).str();
+      item.insertText = Twine(i).str();
+      item.filterText = item.sortText = item.insertText;
+      item.kind = lsp::CompletionItemKind::Field;
+      item.detail = llvm::formatv("{0}: {1}", i, elementTypes[i]);
+      item.insertTextFormat = lsp::InsertTextFormat::PlainText;
+      completionList.items.emplace_back(item);
+
+      // If the element has a name, push back a completion item with that name.
+      if (!elementNames[i].empty()) {
+        item.label =
+            llvm::formatv("{1} (field #{0})", i, elementNames[i]).str();
+        item.filterText = item.label;
+        item.insertText = elementNames[i].str();
+        completionList.items.emplace_back(item);
+      }
+    }
+  }
+
+  void codeCompleteOperationMemberAccess(ast::OperationType opType) final {
+    Optional<StringRef> opName = opType.getName();
+    const ods::Operation *odsOp =
+        opName ? odsContext.lookupOperation(*opName) : nullptr;
+    if (!odsOp)
+      return;
+
+    ArrayRef<ods::OperandOrResult> results = odsOp->getResults();
+    for (const auto &it : llvm::enumerate(results)) {
+      const ods::OperandOrResult &result = it.value();
+      const ods::TypeConstraint &constraint = result.getConstraint();
+
+      // Push back a completion item that uses the result index.
+      lsp::CompletionItem item;
+      item.label = llvm::formatv("{0} (field #{0})", it.index()).str();
+      item.insertText = Twine(it.index()).str();
+      item.filterText = item.sortText = item.insertText;
+      item.kind = lsp::CompletionItemKind::Field;
+      switch (result.getVariableLengthKind()) {
+      case ods::VariableLengthKind::Single:
+        item.detail = llvm::formatv("{0}: Value", it.index()).str();
+        break;
+      case ods::VariableLengthKind::Optional:
+        item.detail = llvm::formatv("{0}: Value?", it.index()).str();
+        break;
+      case ods::VariableLengthKind::Variadic:
+        item.detail = llvm::formatv("{0}: ValueRange", it.index()).str();
+        break;
+      }
+      item.documentation = lsp::MarkupContent{
+          lsp::MarkupKind::Markdown,
+          llvm::formatv("{0}\n\n```c++\n{1}\n```\n", constraint.getSummary(),
+                        constraint.getCppClass())
+              .str()};
+      item.insertTextFormat = lsp::InsertTextFormat::PlainText;
+      completionList.items.emplace_back(item);
+
+      // If the result has a name, push back a completion item with the result
+      // name.
+      if (!result.getName().empty()) {
+        item.label =
+            llvm::formatv("{1} (field #{0})", it.index(), result.getName())
+                .str();
+        item.filterText = item.label;
+        item.insertText = result.getName().str();
+        completionList.items.emplace_back(item);
+      }
+    }
+  }
+
+  void codeCompleteOperationAttributeName(StringRef opName) final {
+    const ods::Operation *odsOp = odsContext.lookupOperation(opName);
+    if (!odsOp)
+      return;
+
+    for (const ods::Attribute &attr : odsOp->getAttributes()) {
+      const ods::AttributeConstraint &constraint = attr.getConstraint();
+
+      lsp::CompletionItem item;
+      item.label = attr.getName().str();
+      item.kind = lsp::CompletionItemKind::Field;
+      item.detail = attr.isOptional() ? "optional" : "";
+      item.documentation = lsp::MarkupContent{
+          lsp::MarkupKind::Markdown,
+          llvm::formatv("{0}\n\n```c++\n{1}\n```\n", constraint.getSummary(),
+                        constraint.getCppClass())
+              .str()};
+      item.insertTextFormat = lsp::InsertTextFormat::PlainText;
+      completionList.items.emplace_back(item);
+    }
+  }
+
+  void codeCompleteConstraintName(ast::Type currentType,
+                                  bool allowNonCoreConstraints,
+                                  bool allowInlineTypeConstraints,
+                                  const ast::DeclScope *scope) final {
+    auto addCoreConstraint = [&](StringRef constraint, StringRef mlirType,
+                                 StringRef snippetText = "") {
+      lsp::CompletionItem item;
+      item.label = constraint.str();
+      item.kind = lsp::CompletionItemKind::Class;
+      item.detail = (constraint + " constraint").str();
+      item.documentation = lsp::MarkupContent{
+          lsp::MarkupKind::Markdown,
+          ("A single entity core constraint of type `" + mlirType + "`").str()};
+      item.sortText = "0";
+      item.insertText = snippetText.str();
+      item.insertTextFormat = snippetText.empty()
+                                  ? lsp::InsertTextFormat::PlainText
+                                  : lsp::InsertTextFormat::Snippet;
+      completionList.items.emplace_back(item);
+    };
+
+    // Insert completions for the core constraints. Some core constraints have
+    // additional characteristics, so we may add then even if a type has been
+    // inferred.
+    if (!currentType) {
+      addCoreConstraint("Attr", "mlir::Attribute");
+      addCoreConstraint("Op", "mlir::Operation *");
+      addCoreConstraint("Value", "mlir::Value");
+      addCoreConstraint("ValueRange", "mlir::ValueRange");
+      addCoreConstraint("Type", "mlir::Type");
+      addCoreConstraint("TypeRange", "mlir::TypeRange");
+    }
+    if (allowInlineTypeConstraints) {
+      /// Attr<Type>.
+      if (!currentType || currentType.isa<ast::AttributeType>())
+        addCoreConstraint("Attr<type>", "mlir::Attribute", "Attr<$1>");
+      /// Value<Type>.
+      if (!currentType || currentType.isa<ast::ValueType>())
+        addCoreConstraint("Value<type>", "mlir::Value", "Value<$1>");
+      /// ValueRange<TypeRange>.
+      if (!currentType || currentType.isa<ast::ValueRangeType>())
+        addCoreConstraint("ValueRange<type>", "mlir::ValueRange",
+                          "ValueRange<$1>");
+    }
+
+    // If a scope was provided, check it for potential constraints.
+    while (scope) {
+      for (const ast::Decl *decl : scope->getDecls()) {
+        if (const auto *cst = dyn_cast<ast::UserConstraintDecl>(decl)) {
+          if (!allowNonCoreConstraints)
+            continue;
+
+          lsp::CompletionItem item;
+          item.label = cst->getName().getName().str();
+          item.kind = lsp::CompletionItemKind::Interface;
+          item.sortText = "2_" + item.label;
+
+          // Skip constraints that are not single-arg. We currently only
+          // complete variable constraints.
+          if (cst->getInputs().size() != 1)
+            continue;
+
+          // Ensure the input type matched the given type.
+          ast::Type constraintType = cst->getInputs()[0]->getType();
+          if (currentType && !currentType.refineWith(constraintType))
+            continue;
+
+          // Format the constraint signature.
+          {
+            llvm::raw_string_ostream strOS(item.detail);
+            strOS << "(";
+            llvm::interleaveComma(
+                cst->getInputs(), strOS, [&](const ast::VariableDecl *var) {
+                  strOS << var->getName().getName() << ": " << var->getType();
+                });
+            strOS << ") -> " << cst->getResultType();
+          }
+
+          completionList.items.emplace_back(item);
+        }
+      }
+
+      scope = scope->getParentScope();
+    }
+  }
+
+  void codeCompleteDialectName() final {
+    // Code complete known dialects.
+    for (const ods::Dialect &dialect : odsContext.getDialects()) {
+      lsp::CompletionItem item;
+      item.label = dialect.getName().str();
+      item.kind = lsp::CompletionItemKind::Class;
+      item.insertTextFormat = lsp::InsertTextFormat::PlainText;
+      completionList.items.emplace_back(item);
+    }
+  }
+
+  void codeCompleteOperationName(StringRef dialectName) final {
+    const ods::Dialect *dialect = odsContext.lookupDialect(dialectName);
+    if (!dialect)
+      return;
+
+    for (const auto &it : dialect->getOperations()) {
+      const ods::Operation &op = *it.second;
+
+      lsp::CompletionItem item;
+      item.label = op.getName().drop_front(dialectName.size() + 1).str();
+      item.kind = lsp::CompletionItemKind::Field;
+      item.insertTextFormat = lsp::InsertTextFormat::PlainText;
+      completionList.items.emplace_back(item);
+    }
+  }
+
+  void codeCompletePatternMetadata() final {
+    auto addSimpleConstraint = [&](StringRef constraint, StringRef desc,
+                                   StringRef snippetText = "") {
+      lsp::CompletionItem item;
+      item.label = constraint.str();
+      item.kind = lsp::CompletionItemKind::Class;
+      item.detail = "pattern metadata";
+      item.documentation =
+          lsp::MarkupContent{lsp::MarkupKind::Markdown, desc.str()};
+      item.insertText = snippetText.str();
+      item.insertTextFormat = snippetText.empty()
+                                  ? lsp::InsertTextFormat::PlainText
+                                  : lsp::InsertTextFormat::Snippet;
+      completionList.items.emplace_back(item);
+    };
+
+    addSimpleConstraint("benefit", "The `benefit` of matching the pattern.",
+                        "benefit($1)");
+    addSimpleConstraint("recursion",
+                        "The pattern properly handles recursive application.");
+  }
+
+private:
+  lsp::CompletionList &completionList;
+  ods::Context &odsContext;
+};
+} // namespace
+
+lsp::CompletionList
+PDLDocument::getCodeCompletion(const lsp::URIForFile &uri,
+                               const lsp::Position &completePos) {
+  SMLoc posLoc = completePos.getAsSMLoc(sourceMgr);
+  if (!posLoc.isValid())
+    return lsp::CompletionList();
+
+  // Adjust the position one further to after the completion trigger token.
+  posLoc = SMLoc::getFromPointer(posLoc.getPointer() + 1);
+
+  // To perform code completion, we run another parse of the module with the
+  // code completion context provided.
+  ods::Context tmpODSContext;
+  lsp::CompletionList completionList;
+  LSPCodeCompleteContext lspCompleteContext(posLoc, completionList,
+                                            tmpODSContext);
+
+  ast::Context tmpContext(tmpODSContext);
+  (void)parsePDLAST(tmpContext, sourceMgr, &lspCompleteContext);
+
+  return completionList;
+}
+
+//===----------------------------------------------------------------------===//
 // PDLTextFileChunk
 //===----------------------------------------------------------------------===//
 
 namespace {
 /// This class represents a single chunk of an PDL text file.
 struct PDLTextFileChunk {
   PDLTextFileChunk(uint64_t lineOffset, const lsp::URIForFile &uri,
                    StringRef contents,
public:
 
   void getLocationsOf(const lsp::URIForFile &uri, lsp::Position defPos,
                       std::vector<lsp::Location> &locations);
   void findReferencesOf(const lsp::URIForFile &uri, lsp::Position pos,
                         std::vector<lsp::Location> &references);
   Optional<lsp::Hover> findHover(const lsp::URIForFile &uri,
                                  lsp::Position hoverPos);
   void findDocumentSymbols(std::vector<lsp::DocumentSymbol> &symbols);
+  lsp::CompletionList getCodeCompletion(const lsp::URIForFile &uri,
+                                        lsp::Position completePos);
 
 private:
   /// Find the PDL document that contains the given position, and update the
   /// position to be anchored at the start of the found chunk instead of the
   /// beginning of the file.
   PDLTextFileChunk &getChunkFor(lsp::Position &pos);
 
   /// The full string contents of the file.
if (i != 0) {
       }
     }
 
     // Push the symbol for this chunk.
     symbols.emplace_back(std::move(symbol));
   }
 }
 
+lsp::CompletionList PDLTextFile::getCodeCompletion(const lsp::URIForFile &uri,
+                                                   lsp::Position completePos) {
+  PDLTextFileChunk &chunk = getChunkFor(completePos);
+  lsp::CompletionList completionList =
+      chunk.document.getCodeCompletion(uri, completePos);
+
+  // Adjust any completion locations.
+  for (lsp::CompletionItem &item : completionList.items) {
+    if (item.textEdit)
+      chunk.adjustLocForChunkOffset(item.textEdit->range);
+    for (lsp::TextEdit &edit : item.additionalTextEdits)
+      chunk.adjustLocForChunkOffset(edit.range);
+  }
+  return completionList;
+}
+
 PDLTextFileChunk &PDLTextFile::getChunkFor(lsp::Position &pos) {
   if (chunks.size() == 1)
     return *chunks.front();
 
   // Search for the first chunk with a greater line offset, the previous chunk
   // is the one that contains `pos`.
   auto it = llvm::upper_bound(
       chunks, pos, [](const lsp::Position &pos, const auto &chunk) {

 }
 
 void lsp::PDLLServer::findDocumentSymbols(
     const URIForFile &uri, std::vector<DocumentSymbol> &symbols) {
   auto fileIt = impl->files.find(uri.file());
   if (fileIt != impl->files.end())
     fileIt->second->findDocumentSymbols(symbols);
 }
+
+lsp::CompletionList
+lsp::PDLLServer::getCodeCompletion(const URIForFile &uri,
+                                   const Position &completePos) {
+  auto fileIt = impl->files.find(uri.file());
+  if (fileIt != impl->files.end())
+    return fileIt->second->getCodeCompletion(uri, completePos);
+  return CompletionList();
+}

mlir/test/mlir-pdll-lsp-server/completion.test

+// RUN: mlir-pdll-lsp-server -lit-test < %s | FileCheck -strict-whitespace %s
+{"jsonrpc":"2.0","id":0,"method":"initialize","params":{"processId":123,"rootPath":"pdll","capabilities":{},"trace":"off"}}
+// -----
+{"jsonrpc":"2.0","method":"textDocument/didOpen","params":{"textDocument":{
+  "uri":"test:///foo.pdll",
+  "languageId":"pdll",
+  "version":1,
+  "text":"Constraint ValueCst(value: Value);\nConstraint Cst();\nPattern FooPattern with benefit(1) {\nlet tuple = (value1 = _: Op, _: Op<test.op>);\nerase tuple.value1;\n}"
+}}}
+// -----
+{"jsonrpc":"2.0","id":1,"method":"textDocument/completion","params":{
+  "textDocument":{"uri":"test:///foo.pdll"},
+  "position":{"line":4,"character":12}
+}}
+//      CHECK:  "id": 1
+// CHECK-NEXT:  "jsonrpc": "2.0",
+// CHECK-NEXT:  "result": {
+// CHECK-NEXT:    "isIncomplete": false,
+// CHECK-NEXT:    "items": [
+// CHECK-NEXT:      {
+// CHECK-NEXT:        "detail": "0: Op",
+// CHECK-NEXT:        "filterText": "0",
+// CHECK-NEXT:        "insertText": "0",
+// CHECK-NEXT:        "insertTextFormat": 1,
+// CHECK-NEXT:        "kind": 5,
+// CHECK-NEXT:        "label": "0 (field #0)",
+// CHECK-NEXT:        "sortText": "0"
+// CHECK-NEXT:      },
+// CHECK-NEXT:      {
+// CHECK-NEXT:        "detail": "0: Op",
+// CHECK-NEXT:        "filterText": "value1 (field #0)",
+// CHECK-NEXT:        "insertText": "value1",
+// CHECK-NEXT:        "insertTextFormat": 1,
+// CHECK-NEXT:        "kind": 5,
+// CHECK-NEXT:        "label": "value1 (field #0)",
+// CHECK-NEXT:        "sortText": "0"
+// CHECK-NEXT:      },
+// CHECK-NEXT:      {
+// CHECK-NEXT:        "detail": "1: Op<test.op>",
+// CHECK-NEXT:        "filterText": "1",
+// CHECK-NEXT:        "insertText": "1",
+// CHECK-NEXT:        "insertTextFormat": 1,
+// CHECK-NEXT:        "kind": 5,
+// CHECK-NEXT:        "label": "1 (field #1)",
+// CHECK-NEXT:        "sortText": "1"
+// CHECK-NEXT:      }
+// CHECK-NEXT:    ]
+// CHECK-NEXT:  }
+// -----
+{"jsonrpc":"2.0","id":1,"method":"textDocument/completion","params":{
+  "textDocument":{"uri":"test:///foo.pdll"},
+  "position":{"line":2,"character":23}
+}}
+//      CHECK:  "id": 1
+// CHECK-NEXT:  "jsonrpc": "2.0",
+// CHECK-NEXT:  "result": {
+// CHECK-NEXT:    "isIncomplete": false,
+// CHECK-NEXT:    "items": [
+// CHECK-NEXT:      {
+// CHECK-NEXT:        "detail": "pattern metadata",
+// CHECK-NEXT:        "documentation": {
+// CHECK-NEXT:          "kind": "markdown",
+// CHECK-NEXT:          "value": "The `benefit` of matching the pattern."
+// CHECK-NEXT:        },
+// CHECK-NEXT:        "insertText": "benefit($1)",
+// CHECK-NEXT:        "insertTextFormat": 2,
+// CHECK-NEXT:        "kind": 7,
+// CHECK-NEXT:        "label": "benefit"
+// CHECK-NEXT:      },
+// CHECK-NEXT:      {
+// CHECK-NEXT:        "detail": "pattern metadata",
+// CHECK-NEXT:        "documentation": {
+// CHECK-NEXT:          "kind": "markdown",
+// CHECK-NEXT:          "value": "The pattern properly handles recursive application."
+// CHECK-NEXT:        },
+// CHECK-NEXT:        "insertTextFormat": 1,
+// CHECK-NEXT:        "kind": 7,
+// CHECK-NEXT:        "label": "recursion"
+// CHECK-NEXT:      }
+// CHECK-NEXT:    ]
+// CHECK-NEXT:  }
+// -----
+{"jsonrpc":"2.0","id":1,"method":"textDocument/completion","params":{
+  "textDocument":{"uri":"test:///foo.pdll"},
+  "position":{"line":3,"character":24}
+}}
+//      CHECK:  "id": 1
+// CHECK-NEXT:  "jsonrpc": "2.0",
+// CHECK-NEXT:  "result": {
+// CHECK-NEXT:    "isIncomplete": false,
+// CHECK-NEXT:    "items": [
+// CHECK-NEXT:      {
+// CHECK-NEXT:        "detail": "Attr constraint",
+// CHECK-NEXT:        "documentation": {
+// CHECK-NEXT:          "kind": "markdown",
+// CHECK-NEXT:          "value": "A single entity core constraint of type `mlir::Attribute`"
+// CHECK-NEXT:        },
+// CHECK-NEXT:        "insertTextFormat": 1,
+// CHECK-NEXT:        "kind": 7,
+// CHECK-NEXT:        "label": "Attr",
+// CHECK-NEXT:        "sortText": "0"
+// CHECK-NEXT:      },
+// CHECK-NEXT:      {
+// CHECK-NEXT:        "detail": "Op constraint",
+// CHECK-NEXT:        "documentation": {
+// CHECK-NEXT:          "kind": "markdown",
+// CHECK-NEXT:          "value": "A single entity core constraint of type `mlir::Operation *`"
+// CHECK-NEXT:        },
+// CHECK-NEXT:        "insertTextFormat": 1,
+// CHECK-NEXT:        "kind": 7,
+// CHECK-NEXT:        "label": "Op",
+// CHECK-NEXT:        "sortText": "0"
+// CHECK-NEXT:      },
+// CHECK-NEXT:      {
+// CHECK-NEXT:        "detail": "Value constraint",
+// CHECK-NEXT:        "documentation": {
+// CHECK-NEXT:          "kind": "markdown",
+// CHECK-NEXT:          "value": "A single entity core constraint of type `mlir::Value`"
+// CHECK-NEXT:        },
+// CHECK-NEXT:        "insertTextFormat": 1,
+// CHECK-NEXT:        "kind": 7,
+// CHECK-NEXT:        "label": "Value",
+// CHECK-NEXT:        "sortText": "0"
+// CHECK-NEXT:      },
+// CHECK-NEXT:      {
+// CHECK-NEXT:        "detail": "ValueRange constraint",
+// CHECK-NEXT:        "documentation": {
+// CHECK-NEXT:          "kind": "markdown",
+// CHECK-NEXT:          "value": "A single entity core constraint of type `mlir::ValueRange`"
+// CHECK-NEXT:        },
+// CHECK-NEXT:        "insertTextFormat": 1,
+// CHECK-NEXT:        "kind": 7,
+// CHECK-NEXT:        "label": "ValueRange",
+// CHECK-NEXT:        "sortText": "0"
+// CHECK-NEXT:      },
+// CHECK-NEXT:      {
+// CHECK-NEXT:        "detail": "Type constraint",
+// CHECK-NEXT:        "documentation": {
+// CHECK-NEXT:          "kind": "markdown",
+// CHECK-NEXT:          "value": "A single entity core constraint of type `mlir::Type`"
+// CHECK-NEXT:        },
+// CHECK-NEXT:        "insertTextFormat": 1,
+// CHECK-NEXT:        "kind": 7,
+// CHECK-NEXT:        "label": "Type",
+// CHECK-NEXT:        "sortText": "0"
+// CHECK-NEXT:      },
+// CHECK-NEXT:      {
+// CHECK-NEXT:        "detail": "TypeRange constraint",
+// CHECK-NEXT:        "documentation": {
+// CHECK-NEXT:          "kind": "markdown",
+// CHECK-NEXT:          "value": "A single entity core constraint of type `mlir::TypeRange`"
+// CHECK-NEXT:        },
+// CHECK-NEXT:        "insertTextFormat": 1,
+// CHECK-NEXT:        "kind": 7,
+// CHECK-NEXT:        "label": "TypeRange",
+// CHECK-NEXT:        "sortText": "0"
+// CHECK-NEXT:      },
+// CHECK-NEXT:      {
+// CHECK-NEXT:        "detail": "Attr<type> constraint",
+// CHECK-NEXT:        "documentation": {
+// CHECK-NEXT:          "kind": "markdown",
+// CHECK-NEXT:          "value": "A single entity core constraint of type `mlir::Attribute`"
+// CHECK-NEXT:        },
+// CHECK-NEXT:        "insertText": "Attr<$1>",
+// CHECK-NEXT:        "insertTextFormat": 2,
+// CHECK-NEXT:        "kind": 7,
+// CHECK-NEXT:        "label": "Attr<type>",
+// CHECK-NEXT:        "sortText": "0"
+// CHECK-NEXT:      },
+// CHECK-NEXT:      {
+// CHECK-NEXT:        "detail": "Value<type> constraint",
+// CHECK-NEXT:        "documentation": {
+// CHECK-NEXT:          "kind": "markdown",
+// CHECK-NEXT:          "value": "A single entity core constraint of type `mlir::Value`"
+// CHECK-NEXT:        },
+// CHECK-NEXT:        "insertText": "Value<$1>",
+// CHECK-NEXT:        "insertTextFormat": 2,
+// CHECK-NEXT:        "kind": 7,
+// CHECK-NEXT:        "label": "Value<type>",
+// CHECK-NEXT:        "sortText": "0"
+// CHECK-NEXT:      },
+// CHECK-NEXT:      {
+// CHECK-NEXT:        "detail": "ValueRange<type> constraint",
+// CHECK-NEXT:        "documentation": {
+// CHECK-NEXT:          "kind": "markdown",
+// CHECK-NEXT:          "value": "A single entity core constraint of type `mlir::ValueRange`"
+// CHECK-NEXT:        },
+// CHECK-NEXT:        "insertText": "ValueRange<$1>",
+// CHECK-NEXT:        "insertTextFormat": 2,
+// CHECK-NEXT:        "kind": 7,
+// CHECK-NEXT:        "label": "ValueRange<type>",
+// CHECK-NEXT:        "sortText": "0"
+// CHECK-NEXT:      },
+// CHECK-NEXT:      {
+// CHECK-NEXT:        "detail": "(value: Value) -> Tuple<>",
+// CHECK-NEXT:        "kind": 8,
+// CHECK-NEXT:        "label": "ValueCst",
+// CHECK-NEXT:        "sortText": "2_ValueCst"
+// CHECK-NEXT:      }
+// CHECK-NEXT:    ]
+// CHECK-NEXT:  }
+// -----
+{"jsonrpc":"2.0","id":3,"method":"shutdown"}
+// -----
+{"jsonrpc":"2.0","method":"exit"}

mlir/test/mlir-pdll-lsp-server/initialize-params.test

 // RUN: mlir-pdll-lsp-server -lit-test < %s | FileCheck %s
 // Test initialize request parameters with rootUri
 {"jsonrpc":"2.0","id":0,"method":"initialize","params":{"processId":123,"rootUri":"test:///workspace","capabilities":{},"trace":"off"}}
 //      CHECK:  "id": 0,
 // CHECK-NEXT:  "jsonrpc": "2.0",
 // CHECK-NEXT:  "result": {
 // CHECK-NEXT:    "capabilities": {
+// CHECK-NEXT:      "completionProvider": {
+// CHECK-NEXT:        "allCommitCharacters": [
+// CHECK:             ],
+// CHECK-NEXT:        "resolveProvider": false,
+// CHECK-NEXT:        "triggerCharacters": [ 
+// CHECK:             ]
+// CHECK-NEXT:      },
 // CHECK-NEXT:      "definitionProvider": true,
 // CHECK-NEXT:      "documentSymbolProvider": true,
 // CHECK-NEXT:      "hoverProvider": true,
 // CHECK-NEXT:      "referencesProvider": true,
 // CHECK-NEXT:      "textDocumentSync": {
 // CHECK-NEXT:        "change": 1,
 // CHECK-NEXT:        "openClose": true,
 // CHECK-NEXT:        "save": true