[Index] Index declarations in lambda expression.

[hokein]

Summary

This fixes clangd couldn't find references for lambda parameters.

[ilya-biryukov]

The RecursiveASTVisitor seems to have the code that properly traverses parameters and return types of lambdas. Any ideas why it's not getting called here?

[hokein]

Update the patch, add comments.

[ilya-biryukov]

Update after investigating with @hokein offline: the RecursiveASTVisitor has custom code to visit lambda parameters and return type, but it fallback to visiting typelocs when both parameters and a return type are specified. Unfortunately this fallback does not work when shouldWalkTypeLocs() is set to false, which is the case for our visitor out here.
It seems reasonable to always visit parameters and return type, rather than relying on traversing the full type-loc of the lamda's function type.

[hokein]

Update the patch.

[hokein]

In D55437#1333145, @ilya-biryukov wrote:

Update after investigating with @hokein offline: the RecursiveASTVisitor has custom code to visit lambda parameters and return type, but it fallback to visiting typelocs when both parameters and a return type are specified. Unfortunately this fallback does not work when shouldWalkTypeLocs() is set to false, which is the case for our visitor out here.
It seems reasonable to always visit parameters and return type, rather than relying on traversing the full type-loc of the lamda's function type.

Thanks! After taking a look at the code closely, it turns out VisitTypeLoc callback gets called when shouldWalkTypeOfTypeLocs is set to false, shouldWalkTypeOfTypeLocs just controls whether we visit the type itself, type loc is always visited.

Unifying code paths of RecursiveASTVisitor seems fine to me, and also simplifies the code of client side, separated in D55820.

[ilya-biryukov]

LGTM

lib/Index/IndexBody.cpp

476

NIT: remove braces around single-statement branch

[hokein]

Rebase and simplify the test.

[hokein]

Fix a nit.

lib/Index/IndexBody.cpp

bool TraverseLambdaCapture(LambdaExpr *LE, const LambdaCapture *C,
     if (C->capturesVariable() && IndexCtx.shouldIndexFunctionLocalSymbols())
       return IndexCtx.handleReference(C->getCapturedVar(), C->getLocation(),
                                       Parent, ParentDC, SymbolRoleSet());
 
     // FIXME: Lambda init-captures.
     return true;
   }
 
+  bool TraverseLambdaExpr(LambdaExpr* LE) {
+    // Clang's default behavior is only visiting the visible parts of lambda
+    // expressions, thus the implicitly (and importantly) generated call
+    // operator is not visited, which results in ignoring parameters of
+    // the lambda expressions.
+    bool Result = RecursiveASTVisitor::TraverseLambdaExpr(LE);
+    // Index parameters of the lambda expressions.
+    if (IndexCtx.shouldIndexFunctionLocalSymbols())
+      for (const auto* PI : LE->getCallOperator()->parameters())
+        IndexCtx.handleDecl(PI);
+    return Result;
+  }
+
   // RecursiveASTVisitor visits both syntactic and semantic forms, duplicating
   // the things that we visit. Make sure to only visit the semantic form.
   // Also visit things that are in the syntactic form but not the semantic one,
   // for example the indices in DesignatedInitExprs.
   bool TraverseInitListExpr(InitListExpr *S, DataRecursionQueue *Q = nullptr) {
     auto visitForm = [&](InitListExpr *Form) {
       for (Stmt *SubStmt : Form->children()) {
         if (!TraverseStmt(SubStmt, Q))
bool VisitOffsetOfExpr(OffsetOfExpr *S) {
     return true;
   }
 };
 
 } // anonymous namespace
 
 void IndexingContext::indexBody(const Stmt *S, const NamedDecl *Parent,
                                 const DeclContext *DC) {
   if (!S)
     return;
 
   if (!DC)
     DC = Parent->getLexicalDeclContext();
   BodyIndexer(*this, Parent, DC).TraverseStmt(const_cast<Stmt*>(S));
 }

test/Index/cxx11-lambdas.cpp

 // RUN: env CINDEXTEST_INDEXLOCALSYMBOLS=1 c-index-test -index-file -std=c++11 %s | FileCheck -check-prefix=CHECK-INDEX %s
 // CHECK-INDEX: [indexEntityReference]: kind: variable | name: localA | USR: c:cxx11-lambdas.cpp@100@S@X@F@f#@localA | lang: C | cursor: VariableRef=localA:6:9 | loc: 7:21
 // CHECK-INDEX: [indexEntityReference]: kind: variable | name: localB | USR: c:cxx11-lambdas.cpp@100@S@X@F@f#@localB | lang: C | cursor: VariableRef=localB:6:17 | loc: 7:29
 // CHECK-INDEX: [indexEntityReference]: kind: typedef | name: Integer | USR: c:cxx11-lambdas.cpp@T@Integer | lang: C | cursor: TypeRef=Integer:3:13 | loc: 7:52
 // CHECK-INDEX: [indexEntityReference]: kind: typedef | name: Integer | USR: c:cxx11-lambdas.cpp@T@Integer | lang: C | cursor: TypeRef=Integer:3:13 | loc: 7:38
 // CHECK-INDEX: [indexEntityReference]: kind: variable | name: localA | USR: c:cxx11-lambdas.cpp@100@S@X@F@f#@localA | lang: C | cursor: DeclRefExpr=localA:6:9 | loc: 8:14
 // CHECK-INDEX: [indexEntityReference]: kind: variable | name: localB | USR: c:cxx11-lambdas.cpp@100@S@X@F@f#@localB | lang: C | cursor: DeclRefExpr=localB:6:17 | loc: 8:23
 // CHECK-INDEX: [indexEntityReference]: kind: variable | name: x | USR: c:cxx11-lambdas.cpp@157@S@X@F@f#@Sa@F@operator()#I#1@x | lang: C | cursor: DeclRefExpr=x:7:46 | loc: 8:32
+// CHECK-INDEX: [indexDeclaration]: kind: variable | name: x | USR: c:cxx11-lambdas.cpp@157@S@X@F@f#@Sa@F@operator()#I#1@x | lang: C | cursor: ParmDecl=x:7:46 (Definition) | loc: 7:46
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