Add a hook RecursiveASTVisitor::TraverseLambdaBody, to enable visitors to

use/maintain additional state from the LambdaExpr while visiting the body
of a LambdaExpr.

One use for this arises because Clang's AST currently holds lambda bodies
in a form prior to their adjustment to refer to captured copies of local
variables, and so some clients will need access to the lambda's closure
type in order to query how to map VarDecl*s to the FieldDecls of their
by-copy captures. This hook is sufficient for at least one such client;
to do this without such a hook would require the client to re-implement
the whole of TraverseLambdaExpr, which is non-trivial and would likely be
more brittle.

llvm-svn: 186024

clang/include/clang/AST/RecursiveASTVisitor.h

@@ -244,7 +244,15 @@ public:
   ///
   /// \returns false if the visitation was terminated early, true otherwise.
   bool TraverseLambdaCapture(LambdaExpr *LE, const LambdaExpr::Capture *C);
-  
+
+  /// \brief Recursively visit the body of a lambda expression.
+  ///
+  /// This provides a hook for visitors that need more context when visiting
+  /// \c LE->getBody().
+  ///
+  /// \returns false if the visitation was terminated early, true otherwise.
+  bool TraverseLambdaBody(LambdaExpr *LE);
+
   // ---- Methods on Stmts ----
 
   // Declare Traverse*() for all concrete Stmt classes.
@@ -809,6 +817,13 @@ bool RecursiveASTVisitor<Derived>::TraverseLambdaCapture(
   return true;
 }
 
+template<typename Derived>
+bool RecursiveASTVisitor<Derived>::TraverseLambdaBody(LambdaExpr *LE) {
+  TRY_TO(TraverseStmt(LE->getBody()));
+  return true;
+}
+
+
 // ----------------- Type traversal -----------------
 
 // This macro makes available a variable T, the passed-in type.
@@ -2153,7 +2168,7 @@ bool RecursiveASTVisitor<Derived>::TraverseLambdaExpr(LambdaExpr *S) {
     }
   }
 
-  TRY_TO(TraverseStmt(S->getBody()));
+  TRY_TO(TraverseLambdaBody(S));
   return true;
 }
 

clang/unittests/Tooling/RecursiveASTVisitorTest.cpp

@@ -9,6 +9,8 @@
 
 #include "TestVisitor.h"
 
+#include <stack>
+
 namespace clang {
 
 class TypeLocVisitor : public ExpectedLocationVisitor<TypeLocVisitor> {
@@ -82,9 +84,25 @@ public:
 class LambdaExprVisitor : public ExpectedLocationVisitor<LambdaExprVisitor> {
 public:
   bool VisitLambdaExpr(LambdaExpr *Lambda) {
+    PendingBodies.push(Lambda);
     Match("", Lambda->getIntroducerRange().getBegin());
     return true;
   }
+  /// For each call to VisitLambdaExpr, we expect a subsequent call (with
+  /// proper nesting) to TraverseLambdaBody.
+  bool TraverseLambdaBody(LambdaExpr *Lambda) {
+    EXPECT_FALSE(PendingBodies.empty());
+    EXPECT_EQ(PendingBodies.top(), Lambda);
+    PendingBodies.pop();
+    return TraverseStmt(Lambda->getBody());
+  }
+  /// Determine whether TraverseLambdaBody has been called for every call to
+  /// VisitLambdaExpr.
+  bool allBodiesHaveBeenTraversed() const {
+    return PendingBodies.empty();
+  }
+private:
+  std::stack<LambdaExpr *> PendingBodies; 
 };
 
 class TemplateArgumentLocTraverser
@@ -478,4 +496,11 @@ TEST(RecursiveASTVisitor, VisitsLambdaExpr) {
 			      LambdaExprVisitor::Lang_CXX11));
 }
 
+TEST(RecursiveASTVisitor, TraverseLambdaBodyCanBeOverridden) {
+  LambdaExprVisitor Visitor;
+  EXPECT_TRUE(Visitor.runOver("void f() { []{ return; }(); }",
+			      LambdaExprVisitor::Lang_CXX11));
+  EXPECT_TRUE(Visitor.allBodiesHaveBeenTraversed());
+}
+
 } // end namespace clang