[clang] fix lambda dependency issue with late parse attributes

[mizvekov]

This fixes a regression introduced in #147835

When parsing a lambda where the call operator has a late parsed attribute, we would try to build a 'this' type for the lambda, but in a lambda 'this' never refers to the lambda class itself.

This late parsed attribute can be added implicitly by the -ftrapping-math flag.

This patch patch makes it so CXXThisScopeRAII ignores lambdas.

This became observable in #147835 because that made clang lazily create tag types, and it removed a workaround for a lambda dependency bug where any previously created tag type for the lambda is discarded after its dependency is recalculated.

But the 'this' scope created above would defeat this laziness and create the lambda type too soon, before its dependency was updated.

Since this regression was never released, there are no release notes.

Fixes #161657

[llvmbot]

@llvm/pr-subscribers-clang

Author: Matheus Izvekov (mizvekov)

Changes

This fixes a regression introduced in #147835

When parsing a lambda where the call operator has a late parsed attribute, we would try to build a 'this' type for the lambda, but in a lambda 'this' never refers to the lambda class itself.

This late parsed attribute can be added implicitly by the -ftrapping-math flag.

This patch patch makes it so CXXThisScopeRAII ignores lambdas.

This became observable in #147835 because that made clang lazily create tag types, and it removed a workaround for a lambda dependency bug where any previously created tag type for the lambda is dicarded after its dependency is recalculated.

But the 'this' scope created above would defeat this laziness and create the lambda type too soon, before its dependency was updated.

Since this regression was never released, there are no release notes.

Fixes #161657

---

Full diff: https://github.com/llvm/llvm-project/pull/161765.diff

2 Files Affected:

• (modified) clang/lib/Sema/SemaExprCXX.cpp (+4)
• (added) clang/test/SemaTemplate/GH161657.cpp (+11)

diff --git a/clang/lib/Sema/SemaExprCXX.cpp b/clang/lib/Sema/SemaExprCXX.cpp
index 779ccf5f1e888..576eb326e6529 100644
--- a/clang/lib/Sema/SemaExprCXX.cpp
+++ b/clang/lib/Sema/SemaExprCXX.cpp
@@ -1251,6 +1251,10 @@ Sema::CXXThisScopeRAII::CXXThisScopeRAII(Sema &S,
   else
     Record = cast<CXXRecordDecl>(ContextDecl);
 
+  // 'this' never refers to the lambda class itself.
+  if (Record->isLambda())
+    return;
+
   QualType T = S.Context.getCanonicalTagType(Record);
   T = S.getASTContext().getQualifiedType(T, CXXThisTypeQuals);
 
diff --git a/clang/test/SemaTemplate/GH161657.cpp b/clang/test/SemaTemplate/GH161657.cpp
new file mode 100644
index 0000000000000..6ec793115db12
--- /dev/null
+++ b/clang/test/SemaTemplate/GH161657.cpp
@@ -0,0 +1,11 @@
+// RUN: %clang_cc1 -fsyntax-only -std=c++20 -ffp-exception-behavior=strict -verify %s
+// expected-no-diagnostics
+
+template <class T> struct S {
+  template <class U> using type1 = decltype([] { return U{}; });
+};
+
+void foo() {
+  using T1 = S<int>::type1<int>;
+  int x = T1()();
+}

[llvm-ci]

LLVM Buildbot has detected a new failure on builder clang-armv8-quick running on linaro-clang-armv8-quick while building clang at step 5 "ninja check 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/154/builds/22270

Here is the relevant piece of the build log for the reference

Step 5 (ninja check 1) failure: stage 1 checked (failure)
******************** TEST 'Clang :: SemaTemplate/GH161657.cpp' FAILED ********************
Exit Code: 1

Command Output (stderr):
--
/home/tcwg-buildbot/worker/clang-armv8-quick/stage1/bin/clang -cc1 -internal-isystem /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/lib/clang/22/include -nostdsysteminc -fsyntax-only -std=c++20 -ffp-exception-behavior=strict -verify /home/tcwg-buildbot/worker/clang-armv8-quick/llvm/clang/test/SemaTemplate/GH161657.cpp # RUN: at line 1
+ /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/bin/clang -cc1 -internal-isystem /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/lib/clang/22/include -nostdsysteminc -fsyntax-only -std=c++20 -ffp-exception-behavior=strict -verify /home/tcwg-buildbot/worker/clang-armv8-quick/llvm/clang/test/SemaTemplate/GH161657.cpp
error: 'expected-warning' diagnostics seen but not expected: 
  (frontend): overriding currently unsupported use of floating point exceptions on this target
1 error generated.

--

********************

[llvm-ci]

LLVM Buildbot has detected a new failure on builder clang-solaris11-sparcv9 running on solaris11-sparcv9 while building clang at step 5 "ninja check 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/13/builds/9848

Here is the relevant piece of the build log for the reference

Step 5 (ninja check 1) failure: stage 1 checked (failure)
******************** TEST 'Clang :: SemaTemplate/GH161657.cpp' FAILED ********************
Exit Code: 1

Command Output (stderr):
--
/opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/stage1/bin/clang -cc1 -internal-isystem /opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/stage1/lib/clang/22/include -nostdsysteminc -fsyntax-only -std=c++20 -ffp-exception-behavior=strict -verify /opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/llvm/clang/test/SemaTemplate/GH161657.cpp # RUN: at line 1
+ /opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/stage1/bin/clang -cc1 -internal-isystem /opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/stage1/lib/clang/22/include -nostdsysteminc -fsyntax-only -std=c++20 -ffp-exception-behavior=strict -verify /opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/llvm/clang/test/SemaTemplate/GH161657.cpp
error: 'expected-warning' diagnostics seen but not expected: 
  (frontend): overriding currently unsupported use of floating point exceptions on this target
1 error generated.

--

********************

[llvm-ci]

LLVM Buildbot has detected a new failure on builder clang-armv7-global-isel running on linaro-clang-armv7-global-isel while building clang at step 7 "ninja check 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/39/builds/8112

Here is the relevant piece of the build log for the reference

Step 7 (ninja check 1) failure: stage 1 checked (failure)
******************** TEST 'Clang :: SemaTemplate/GH161657.cpp' FAILED ********************
Exit Code: 1

Command Output (stderr):
--
/home/tcwg-buildbot/worker/clang-armv7-global-isel/stage1/bin/clang -cc1 -internal-isystem /home/tcwg-buildbot/worker/clang-armv7-global-isel/stage1/lib/clang/22/include -nostdsysteminc -fsyntax-only -std=c++20 -ffp-exception-behavior=strict -verify /home/tcwg-buildbot/worker/clang-armv7-global-isel/llvm/clang/test/SemaTemplate/GH161657.cpp # RUN: at line 1
+ /home/tcwg-buildbot/worker/clang-armv7-global-isel/stage1/bin/clang -cc1 -internal-isystem /home/tcwg-buildbot/worker/clang-armv7-global-isel/stage1/lib/clang/22/include -nostdsysteminc -fsyntax-only -std=c++20 -ffp-exception-behavior=strict -verify /home/tcwg-buildbot/worker/clang-armv7-global-isel/llvm/clang/test/SemaTemplate/GH161657.cpp
error: 'expected-warning' diagnostics seen but not expected: 
  (frontend): overriding currently unsupported use of floating point exceptions on this target
1 error generated.

--

********************

[llvm-ci]

LLVM Buildbot has detected a new failure on builder llvm-clang-win-x-armv7l running on as-builder-1 while building clang at step 10 "test-check-clang".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/38/builds/5688

Here is the relevant piece of the build log for the reference

Step 10 (test-check-clang) failure: Test just built components: check-clang completed (failure)
******************** TEST 'Clang :: SemaTemplate/GH161657.cpp' FAILED ********************
Exit Code: 1

Command Output (stdout):
--
# RUN: at line 1
c:\buildbot\as-builder-1\x-armv7l\build\bin\clang.exe -cc1 -internal-isystem C:\buildbot\as-builder-1\x-armv7l\build\lib\clang\22\include -nostdsysteminc -fsyntax-only -std=c++20 -ffp-exception-behavior=strict -verify C:\buildbot\as-builder-1\x-armv7l\llvm-project\clang\test\SemaTemplate\GH161657.cpp
# executed command: 'c:\buildbot\as-builder-1\x-armv7l\build\bin\clang.exe' -cc1 -internal-isystem 'C:\buildbot\as-builder-1\x-armv7l\build\lib\clang\22\include' -nostdsysteminc -fsyntax-only -std=c++20 -ffp-exception-behavior=strict -verify 'C:\buildbot\as-builder-1\x-armv7l\llvm-project\clang\test\SemaTemplate\GH161657.cpp'
# .---command stderr------------
# | error: 'expected-warning' diagnostics seen but not expected: 
# |   (frontend): overriding currently unsupported use of floating point exceptions on this target
# | 1 error generated.
# `-----------------------------
# error: command failed with exit status: 1

--

********************