[clang][dataflow] Add captured parameters to ReferencedDecls for lamb… (#117771)

…da call operators.

This doesn't require that they be used in the operator's body, unlike
other ReferencedDecls. This is most obviously different from captured
local variables, which can be captured but will not appear in
ReferencedDecls unless they appear in the operator's body.

This difference simplifies the collection of the captured parameters,
but probably could be eliminated if desirable.

Author: bazuzi

clang/include/clang/Analysis/FlowSensitive/ASTOps.h

@@ -146,6 +146,10 @@ struct ReferencedDecls {
   /// Free functions and member functions which are referenced (but not
   /// necessarily called).
   llvm::DenseSet<const FunctionDecl *> Functions;
+  /// When analyzing a lambda's call operator, the set of all parameters (from
+  /// the surrounding function) that the lambda captures. Captured local
+  /// variables are already included in `Locals` above.
+  llvm::DenseSet<const ParmVarDecl *> LambdaCapturedParams;
 };
 
 /// Returns declarations that are declared in or referenced from `FD`.

clang/lib/Analysis/FlowSensitive/ASTOps.cpp

@@ -11,6 +11,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "clang/Analysis/FlowSensitive/ASTOps.h"
+#include "clang/AST/ASTLambda.h"
 #include "clang/AST/ComputeDependence.h"
 #include "clang/AST/Decl.h"
 #include "clang/AST/DeclBase.h"
@@ -282,6 +283,28 @@ ReferencedDecls getReferencedDecls(const FunctionDecl &FD) {
   if (const auto *CtorDecl = dyn_cast<CXXConstructorDecl>(&FD))
     Visitor.traverseConstructorInits(CtorDecl);
 
+  // If analyzing a lambda call operator, collect all captures of parameters (of
+  // the surrounding function). This collects them even if they are not
+  // referenced in the body of the lambda call operator. Non-parameter local
+  // variables that are captured are already collected into
+  // `ReferencedDecls.Locals` when traversing the call operator body, but we
+  // collect parameters here to avoid needing to check at each referencing node
+  // whether the parameter is a lambda capture from a surrounding function or is
+  // a parameter of the current function. If it becomes necessary to limit this
+  // set to the parameters actually referenced in the body, alternative
+  // optimizations can be implemented to minimize duplicative work.
+  if (const auto *Method = dyn_cast<CXXMethodDecl>(&FD);
+      Method && isLambdaCallOperator(Method)) {
+    for (const auto &Capture : Method->getParent()->captures()) {
+      if (Capture.capturesVariable()) {
+        if (const auto *Param =
+                dyn_cast<ParmVarDecl>(Capture.getCapturedVar())) {
+          Result.LambdaCapturedParams.insert(Param);
+        }
+      }
+    }
+  }
+
   return Result;
 }
 

clang/unittests/Analysis/FlowSensitive/ASTOpsTest.cpp

@@ -8,15 +8,23 @@
 
 #include "clang/Analysis/FlowSensitive/ASTOps.h"
 #include "TestingSupport.h"
+#include "clang/AST/Decl.h"
+#include "clang/AST/DeclCXX.h"
+#include "clang/ASTMatchers/ASTMatchers.h"
+#include "clang/Basic/LLVM.h"
+#include "clang/Frontend/ASTUnit.h"
+#include "clang/Tooling/Tooling.h"
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
 #include <memory>
+#include <string>
 
 namespace {
 
 using namespace clang;
 using namespace dataflow;
 
+using ast_matchers::cxxMethodDecl;
 using ast_matchers::cxxRecordDecl;
 using ast_matchers::hasName;
 using ast_matchers::hasType;
@@ -107,4 +115,37 @@ TEST(ASTOpsTest, ReferencedDeclsLocalsNotParamsOrStatics) {
               UnorderedElementsAre(LocalDecl));
 }
 
+TEST(ASTOpsTest, LambdaCaptures) {
+  std::string Code = R"cc(
+    void func(int CapturedByRef, int CapturedByValue, int NotCaptured) {
+    int Local;
+      auto Lambda = [&CapturedByRef, CapturedByValue, &Local](int LambdaParam) {
+      };
+    }
+  )cc";
+  std::unique_ptr<ASTUnit> Unit =
+      tooling::buildASTFromCodeWithArgs(Code, {"-fsyntax-only", "-std=c++17"});
+  auto &ASTCtx = Unit->getASTContext();
+
+  ASSERT_EQ(ASTCtx.getDiagnostics().getClient()->getNumErrors(), 0U);
+
+  auto *LambdaCallOp = selectFirst<CXXMethodDecl>(
+      "l", match(cxxMethodDecl(hasName("operator()")).bind("l"), ASTCtx));
+  ASSERT_NE(LambdaCallOp, nullptr);
+  auto *Func = cast<FunctionDecl>(findValueDecl(ASTCtx, "func"));
+  ASSERT_NE(Func, nullptr);
+  auto *CapturedByRefDecl = Func->getParamDecl(0);
+  ASSERT_NE(CapturedByRefDecl, nullptr);
+  auto *CapturedByValueDecl = Func->getParamDecl(1);
+  ASSERT_NE(CapturedByValueDecl, nullptr);
+
+  EXPECT_THAT(getReferencedDecls(*Func).LambdaCapturedParams, IsEmpty());
+  ReferencedDecls ForLambda = getReferencedDecls(*LambdaCallOp);
+  EXPECT_THAT(ForLambda.LambdaCapturedParams,
+              UnorderedElementsAre(CapturedByRefDecl, CapturedByValueDecl));
+  // Captured locals must be seen in the body for them to appear in
+  // ReferencedDecls.
+  EXPECT_THAT(ForLambda.Locals, IsEmpty());
+}
+
 } // namespace