[PATCH] D139125: [clang] Correctly handle by-reference capture with an initializer that is a pack expansion in lambdas.

[Jens Massberg via Phabricator via cfe-commits]

massberg updated this revision to Diff 480475.
massberg added a comment.

Moved check if we have a pack expansion with reference type to Sema::BuildLambdaExpr.

I'm still not sure if this is the right place, or if `From.isCopyCapture()` should be `false` for pack expansions with refernece types.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D139125/new/

https://reviews.llvm.org/D139125

Files:
  clang/lib/Sema/SemaLambda.cpp
  clang/lib/Sema/TreeTransform.h
  clang/test/SemaCXX/lambda-pack-expansion.cpp
  clang/unittests/ASTMatchers/ASTMatchersNodeTest.cpp


Index: clang/unittests/ASTMatchers/ASTMatchersNodeTest.cpp
===================================================================
--- clang/unittests/ASTMatchers/ASTMatchersNodeTest.cpp
+++ clang/unittests/ASTMatchers/ASTMatchersNodeTest.cpp
@@ -2306,6 +2306,30 @@
           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"))));
Index: clang/test/SemaCXX/lambda-pack-expansion.cpp
===================================================================
--- /dev/null
+++ 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);
+}
+}
Index: clang/lib/Sema/TreeTransform.h
===================================================================
--- clang/lib/Sema/TreeTransform.h
+++ clang/lib/Sema/TreeTransform.h
@@ -13147,9 +13147,10 @@
       }
       Expr *NewExprInit = NewExprInitResult.get();
 
+      bool isReferenceType = (C->getCaptureKind() == LCK_ByRef);
       QualType NewInitCaptureType =
           getSema().buildLambdaInitCaptureInitialization(
-              C->getLocation(), OldVD->getType()->isReferenceType(),
+              C->getLocation(), isReferenceType,
               EllipsisLoc, NumExpansions, OldVD->getIdentifier(),
               cast<VarDecl>(C->getCapturedVar())->getInitStyle() !=
                   VarDecl::CInit,
Index: clang/lib/Sema/SemaLambda.cpp
===================================================================
--- clang/lib/Sema/SemaLambda.cpp
+++ clang/lib/Sema/SemaLambda.cpp
@@ -1900,6 +1900,12 @@
           ValueDecl *Var = From.getVariable();
           LambdaCaptureKind Kind =
               From.isCopyCapture() ? LCK_ByCopy : LCK_ByRef;
+          if (isa<PackExpansionType>(Var->getType()) &&
+              cast<PackExpansionType>(Var->getType())
+                                        ->getPattern()
+              ->isReferenceType()) {
+            Kind = LCK_ByRef;
+          }
           return LambdaCapture(From.getLocation(), IsImplicit, Kind, Var,
                                From.getEllipsisLoc());
         }


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