[clang] [Clang] Don't add top-level const qualifiers to captured function types (PR #118050)

[Younan Zhang via cfe-commits]

https://github.com/zyn0217 updated https://github.com/llvm/llvm-project/pull/118050

>From 92b8a28eb7664b3cac6a8039834b099b010af3ed Mon Sep 17 00:00:00 2001
From: Younan Zhang <zyn7109 at gmail.com>
Date: Fri, 29 Nov 2024 13:19:30 +0800
Subject: [PATCH 1/2] [Clang] Don't add top-level const qualifiers to captured
 function types

---
 clang/docs/ReleaseNotes.rst                        |  1 +
 clang/lib/Sema/SemaExpr.cpp                        | 11 +++++++++--
 .../test/SemaCXX/lambda-capture-type-deduction.cpp | 14 ++++++++++++++
 3 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 8bd06fadfdc984..553856f3060bc1 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -712,6 +712,7 @@ Bug Fixes to C++ Support
 - Name independent data members were not correctly initialized from default member initializers. (#GH114069)
 - Fixed expression transformation for ``[[assume(...)]]``, allowing using pack indexing expressions within the
   assumption if they also occur inside of a dependent lambda. (#GH114787)
+- Lambdas now capture function types without considering top-level const qualifiers. (#GH84961)
 - Clang now uses valid deduced type locations when diagnosing functions with trailing return type
   missing placeholder return type. (#GH78694)
 
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index 6c7472ce92703b..04b713a91dedfa 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -18479,7 +18479,10 @@ static bool isVariableAlreadyCapturedInScopeInfo(CapturingScopeInfo *CSI,
     // are mutable in the sense that user can change their value - they are
     // private instances of the captured declarations.
     const Capture &Cap = CSI->getCapture(Var);
-    if (Cap.isCopyCapture() &&
+    // C++ [dcl.fct]p7:
+    //   [When] adding cv-qualifications on top of the function type [...] the
+    //   cv-qualifiers are ignored.
+    if (Cap.isCopyCapture() && !DeclRefType->isFunctionType() &&
         !(isa<LambdaScopeInfo>(CSI) &&
           !cast<LambdaScopeInfo>(CSI)->lambdaCaptureShouldBeConst()) &&
         !(isa<CapturedRegionScopeInfo>(CSI) &&
@@ -18789,7 +18792,11 @@ static bool captureInLambda(LambdaScopeInfo *LSI, ValueDecl *Var,
     //   parameter-declaration-clause is not followed by mutable.
     DeclRefType = CaptureType.getNonReferenceType();
     bool Const = LSI->lambdaCaptureShouldBeConst();
-    if (Const && !CaptureType->isReferenceType())
+    // C++ [dcl.fct]p7:
+    //   [When] adding cv-qualifications on top of the function type [...] the
+    //   cv-qualifiers are ignored.
+    if (Const && !CaptureType->isReferenceType() &&
+        !DeclRefType->isFunctionType())
       DeclRefType.addConst();
   }
 
diff --git a/clang/test/SemaCXX/lambda-capture-type-deduction.cpp b/clang/test/SemaCXX/lambda-capture-type-deduction.cpp
index a86f3018989927..ba7ab34f943be1 100644
--- a/clang/test/SemaCXX/lambda-capture-type-deduction.cpp
+++ b/clang/test/SemaCXX/lambda-capture-type-deduction.cpp
@@ -319,3 +319,17 @@ constexpr void foo() {
 }
 
 } // namespace GH47400
+
+namespace GH84961 {
+
+template <typename T> void g(const T &t) {}
+
+template <typename T> void f(const T &t) {
+  [t] { g(t); }();
+}
+
+void h() {
+  f(h);
+}
+
+} // namespace GH84961

>From 1ce64b5c1339a1ee22cf6df47a3ba3cb1ebf4bfb Mon Sep 17 00:00:00 2001
From: Younan Zhang <zyn7109 at gmail.com>
Date: Wed, 4 Dec 2024 13:30:16 +0800
Subject: [PATCH 2/2] Refer to [expr.prim.lambda]p10

---
 clang/lib/Sema/SemaExpr.cpp | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index 04b713a91dedfa..47612ef2effb95 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -18479,9 +18479,10 @@ static bool isVariableAlreadyCapturedInScopeInfo(CapturingScopeInfo *CSI,
     // are mutable in the sense that user can change their value - they are
     // private instances of the captured declarations.
     const Capture &Cap = CSI->getCapture(Var);
-    // C++ [dcl.fct]p7:
-    //   [When] adding cv-qualifications on top of the function type [...] the
-    //   cv-qualifiers are ignored.
+    // C++ [expr.prim.lambda]p10:
+    //   The type of such a data member is [...] an lvalue reference to the
+    //   referenced function type if the entity is a reference to a function.
+    //   [...]
     if (Cap.isCopyCapture() && !DeclRefType->isFunctionType() &&
         !(isa<LambdaScopeInfo>(CSI) &&
           !cast<LambdaScopeInfo>(CSI)->lambdaCaptureShouldBeConst()) &&
@@ -18792,9 +18793,10 @@ static bool captureInLambda(LambdaScopeInfo *LSI, ValueDecl *Var,
     //   parameter-declaration-clause is not followed by mutable.
     DeclRefType = CaptureType.getNonReferenceType();
     bool Const = LSI->lambdaCaptureShouldBeConst();
-    // C++ [dcl.fct]p7:
-    //   [When] adding cv-qualifications on top of the function type [...] the
-    //   cv-qualifiers are ignored.
+    // C++ [expr.prim.lambda]p10:
+    //   The type of such a data member is [...] an lvalue reference to the
+    //   referenced function type if the entity is a reference to a function.
+    //   [...]
     if (Const && !CaptureType->isReferenceType() &&
         !DeclRefType->isFunctionType())
       DeclRefType.addConst();