[clangd] Ignore more implicit nodes in computing selection.

[sammccall]

Summary

The DeclRefExpr for the callee of overloaded operator() and operator[] are
assigned the range of the paren/bracket lists in the AST.
These are better thought of as implicit (at least () - `[] is murkier).
But there's no bit on Expr for implicit, so just ignore them on our side.

While here, deal with the case where an implicit stmt (e.g. implicit-this)
is wrapped in an implicit cast. Previously we ignored the statement but not
the cast, and so the cast ended up being selected.

Fixes https://github.com/clangd/clangd/issues/195

[merge_guards_bot]

Build result: pass - 59972 tests passed, 0 failed and 763 were skipped.
Log files: console-log.txt, CMakeCache.txt

[kadircet]

LGTM, thanks!

clang-tools-extra/clangd/Selection.cpp

162

nit: braces

163

nit: braces

clang-tools-extra/clangd/Selection.cpp

 //===--- Selection.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 "Selection.h"
 #include "Logger.h"
 #include "SourceCode.h"
 #include "clang/AST/ASTTypeTraits.h"
+#include "clang/AST/Expr.h"
 #include "clang/AST/PrettyPrinter.h"
 #include "clang/AST/RecursiveASTVisitor.h"
 #include "clang/AST/TypeLoc.h"
+#include "clang/Basic/OperatorKinds.h"
 #include "clang/Basic/SourceLocation.h"
 #include "clang/Basic/SourceManager.h"
 #include "clang/Basic/TokenKinds.h"
 #include "clang/Lex/Lexer.h"
 #include "clang/Tooling/Syntax/Tokens.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/raw_ostream.h"
std::string printNodeToString(const DynTypedNode &N, const PrintingPolicy &PP) {
   std::string S;
   llvm::raw_string_ostream OS(S);
   printNodeKind(OS, N);
   OS << " ";
   return std::move(OS.str());
 }
 #endif
 
+bool isImplicit(const Stmt* S) {
+  // Some Stmts are implicit and shouldn't be traversed, but there's no
+  // "implicit" attribute on Stmt/Expr.
+  // Unwrap implicit casts first if present (other nodes too?).
+  if (auto *ICE = llvm::dyn_cast<ImplicitCastExpr>(S))
+    S = ICE->getSubExprAsWritten();
+  // Implicit this in a MemberExpr is not filtered out by RecursiveASTVisitor.
+  // It would be nice if RAV handled this (!shouldTraverseImplicitCode()).
+  if (auto *CTI = llvm::dyn_cast<CXXThisExpr>(S))
+    if (CTI->isImplicit())
+      return true;
+  // Refs to operator() and [] are (almost?) always implicit as part of calls.
+  if (auto *DRE = llvm::dyn_cast<DeclRefExpr>(S)) {
+    if (auto *FD = llvm::dyn_cast<FunctionDecl>(DRE->getDecl())) {
+      switch (FD->getOverloadedOperator()) {
+      case OO_Call:
+      case OO_Subscript:
+        return true;
+      default:
+        break;
+      }
+    }
+  }
+  return false;
+}
+
 // We find the selection by visiting written nodes in the AST, looking for nodes
 // that intersect with the selected character range.
 //
 // While traversing, we maintain a parent stack. As nodes pop off the stack,
 // we decide whether to keep them or not. To be kept, they must either be
 // selected or contain some nodes that are.
 //
 // For simple cases (not inside macros) we prune subtrees that don't intersect.
return traverseNode(
         &X, [&] { return Base::TraverseNestedNameSpecifierLoc(X); });
   }
   bool TraverseConstructorInitializer(CXXCtorInitializer *X) {
     return traverseNode(
         X, [&] { return Base::TraverseConstructorInitializer(X); });
   }
   // Stmt is the same, but this form allows the data recursion optimization.
   bool dataTraverseStmtPre(Stmt *X) {
-    if (!X)
-      return false;
-    // Implicit this in a MemberExpr is not filtered out by RecursiveASTVisitor.
-    // It would be nice if RAV handled this (!shouldTRaverseImplicitCode()).
-    if (auto *CTI = llvm::dyn_cast<CXXThisExpr>(X))
-      if (CTI->isImplicit())
-        return false;
+    if (!X || isImplicit(X))
     auto N = DynTypedNode::create(*X);
     if (canSafelySkipNode(N))
       return false;
     push(std::move(N));
     return true;
   }
   bool dataTraverseStmtPost(Stmt *X) {
     pop();

clang-tools-extra/clangd/unittests/SelectionTests.cpp

Case Cases[] = {
           R"cpp(
             [[void ^(*S)(int)]] = nullptr;
           )cpp",
           "FunctionProtoTypeLoc",
       },
       {
           R"cpp(
             struct S {
-              int foo;
-              int bar() { return [[f^oo]]; }
+              int foo() const;
+              int bar() { return [[f^oo]](); }
             };
           )cpp",
-          "MemberExpr", // Not implicit CXXThisExpr!
+          "MemberExpr", // Not implicit CXXThisExpr, or its implicit cast!
+      },
+      {
+          R"cpp(
+            auto lambda = [](const char*){ return 0; };
+            int x = lambda([["y^"]]);
+          )cpp",
+          "StringLiteral", // Not DeclRefExpr to operator()!
       },
 
       // Point selections.
       {"void foo() { [[^foo]](); }", "DeclRefExpr"},
       {"void foo() { [[f^oo]](); }", "DeclRefExpr"},
       {"void foo() { [[fo^o]](); }", "DeclRefExpr"},
       {"void foo() { [[foo^()]]; }", "CallExpr"},
       {"void foo() { [[foo^]] (); }", "DeclRefExpr"},