[clang] Correctly handle by-reference capture with an initializer tha…

…t is a pack expansion in lambdas.

Ensure that the correct information whether an init-capture of a lambda
is passed by reference or by copy. This information is already computed
and has to be passed to the place where `NewInitCaptureType` is
created.

Before this fix it has been checked whether the VarDecl is a reference
type. This doesn't work for packed expansions, as the information
whether it is passed by reference or by copy is stored at the pattern of
a `PackExpansionType` and not at the type itself.

However, as the information has been already computed, we just have to
pass it.

Add tests that lambda captures with var decls which are reference types
are created in the AST and a disgnotics test for pack expansions.

Fixes #49266

Differential Revision: https://reviews.llvm.org/D139125

clang/include/clang/Sema/Sema.h

@@ -7097,7 +7097,8 @@ class Sema final {
                                           unsigned InitStyle, Expr *Init);
 
   /// Add an init-capture to a lambda scope.
-  void addInitCapture(sema::LambdaScopeInfo *LSI, VarDecl *Var);
+  void addInitCapture(sema::LambdaScopeInfo *LSI, VarDecl *Var,
+                      bool isReferenceType);
 
   /// Note that we have finished the explicit captures for the
   /// given lambda.

clang/lib/Sema/SemaLambda.cpp

@@ -887,11 +887,12 @@ VarDecl *Sema::createLambdaInitCaptureVarDecl(SourceLocation Loc,
   return NewVD;
 }
 
-void Sema::addInitCapture(LambdaScopeInfo *LSI, VarDecl *Var) {
+void Sema::addInitCapture(LambdaScopeInfo *LSI, VarDecl *Var,
+                          bool isReferenceType) {
   assert(Var->isInitCapture() && "init capture flag should be set");
-  LSI->addCapture(Var, /*isBlock*/false, Var->getType()->isReferenceType(),
-                  /*isNested*/false, Var->getLocation(), SourceLocation(),
-                  Var->getType(), /*Invalid*/false);
+  LSI->addCapture(Var, /*isBlock*/ false, isReferenceType,
+                  /*isNested*/ false, Var->getLocation(), SourceLocation(),
+                  Var->getType(), /*Invalid*/ false);
 }
 
 void Sema::ActOnStartOfLambdaDefinition(LambdaIntroducer &Intro,
@@ -1261,7 +1262,7 @@ void Sema::ActOnStartOfLambdaDefinition(LambdaIntroducer &Intro,
     }
 
     if (C->Init.isUsable()) {
-      addInitCapture(LSI, cast<VarDecl>(Var));
+      addInitCapture(LSI, cast<VarDecl>(Var), C->Kind == LCK_ByRef);
     } else {
       TryCaptureKind Kind = C->Kind == LCK_ByRef ? TryCapture_ExplicitByRef :
                                                    TryCapture_ExplicitByVal;

clang/lib/Sema/TreeTransform.h

@@ -13149,7 +13149,7 @@ TreeTransform<Derived>::TransformLambdaExpr(LambdaExpr *E) {
 
       QualType NewInitCaptureType =
           getSema().buildLambdaInitCaptureInitialization(
-              C->getLocation(), OldVD->getType()->isReferenceType(),
+              C->getLocation(), C->getCaptureKind() == LCK_ByRef,
               EllipsisLoc, NumExpansions, OldVD->getIdentifier(),
               cast<VarDecl>(C->getCapturedVar())->getInitStyle() !=
                   VarDecl::CInit,
@@ -13331,7 +13331,7 @@ TreeTransform<Derived>::TransformLambdaExpr(LambdaExpr *E) {
           break;
         }
         NewVDs.push_back(NewVD);
-        getSema().addInitCapture(LSI, NewVD);
+        getSema().addInitCapture(LSI, NewVD, C->getCaptureKind() == LCK_ByRef);
       }
 
       if (Invalid)

clang/test/SemaCXX/lambda-pack-expansion.cpp

@@ -0,0 +1,22 @@
+// RUN: %clang_cc1 -std=c++20 -Wno-unused-value -fsyntax-only -verify %s
+
+namespace GH49266 {
+struct X {
+  X() = default;
+  X(X const&) = delete; // expected-note {{'X' has been explicitly marked deleted here}}
+};
+
+void take_by_copy(auto &...args) {
+  [...args = args] {}(); // expected-error {{call to deleted constructor}}
+}
+
+void take_by_ref(auto &...args) {
+  [&...args = args] {}(); // args is passed by reference and not copied.
+}
+
+void foo() {
+  X x;
+  take_by_copy(x); // expected-note {{in instantiation of function template specialization}}
+  take_by_ref(x);
+}
+}

clang/unittests/ASTMatchers/ASTMatchersNodeTest.cpp

@@ -2306,6 +2306,30 @@ TEST_P(ASTMatchersTest,
           hasName("cc"), hasInitializer(integerLiteral(equals(1))))))))));
 }
 
+TEST_P(ASTMatchersTest, LambdaCaptureTest_BindsToCaptureOfReferenceType) {
+  if (!GetParam().isCXX20OrLater()) {
+    return;
+  }
+  auto matcher = lambdaExpr(hasAnyCapture(
+      lambdaCapture(capturesVar(varDecl(hasType(referenceType()))))));
+  EXPECT_TRUE(matches("template <class ...T> void f(T &...args) {"
+                      "  [&...args = args] () mutable {"
+                      "  }();"
+                      "}"
+                      "int main() {"
+                      "  int a;"
+                      "  f(a);"
+                      "}", matcher));
+  EXPECT_FALSE(matches("template <class ...T> void f(T &...args) {"
+                       "  [...args = args] () mutable {"
+                       "  }();"
+                       "}"
+                       "int main() {"
+                       "  int a;"
+                       "  f(a);"
+                       "}", matcher));
+}
+
 TEST(ASTMatchersTestObjC, ObjCMessageCalees) {
   StatementMatcher MessagingFoo =
       objcMessageExpr(callee(objcMethodDecl(hasName("foo"))));