[clang] [clang][Sema] Fix rejected-valid for explicit object parameters in dependent nested classes context (PR #209107)

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<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Weibo He (NewSigma)

<details>
<summary>Changes</summary>

In #<!-- -->89078, we banned explicit object parameters from several invalid contexts. This patch proposes we relax the restriction and allow entering contexts so that nested classes can be visited correctly.

Close #<!-- -->136472 


---
Full diff: https://github.com/llvm/llvm-project/pull/209107.diff


3 Files Affected:

- (modified) clang/docs/ReleaseNotes.md (+1) 
- (modified) clang/lib/Sema/SemaType.cpp (+2-1) 
- (modified) clang/test/SemaCXX/cxx2b-deducing-this.cpp (+13) 


``````````diff
diff --git a/clang/docs/ReleaseNotes.md b/clang/docs/ReleaseNotes.md
index bbd42848a98c2..604b1c50241d5 100644
--- a/clang/docs/ReleaseNotes.md
+++ b/clang/docs/ReleaseNotes.md
@@ -814,6 +814,7 @@ latest release, please see the [Clang Web Site](https://clang.llvm.org) or the
   would only use the first one). A new warning that diagnoses such declarations has been added to `-Wignored-attributes`.
   (#GH191829)
 - Fixed a crash in the constant evaluator when an ill-formed array new-expression whose bound could not be determined (e.g. `new int[]()`) was used in a constant expression. (#GH200139)
+- Fixed a rejected-valid case that used explicit object parameters in the context of dependent nested classes. (#GH136472)
 - Clang now defines the GCC-compatible predefined macros `__WCHAR_MIN__`, `__WINT_MIN__`, and `__SIG_ATOMIC_MIN__`. (#GH199678)
 - Fix a crash in addUnsizedArray due assert not verifying we have a Base before doing checks on it. (#GH44212)
 
diff --git a/clang/lib/Sema/SemaType.cpp b/clang/lib/Sema/SemaType.cpp
index 3f0a7304db2f9..96e42b2bf9fe7 100644
--- a/clang/lib/Sema/SemaType.cpp
+++ b/clang/lib/Sema/SemaType.cpp
@@ -4890,7 +4890,8 @@ static TypeSourceInfo *GetFullTypeForDeclarator(TypeProcessingState &state,
         // If there already was an problem with the scope, don’t issue another
         // error about the explicit object parameter.
         return SS.isInvalid() ||
-               isa_and_present<CXXRecordDecl>(S.computeDeclContext(SS));
+               isa_and_present<CXXRecordDecl>(
+                   S.computeDeclContext(SS, /*EnteringContext=*/true));
       };
 
       // C++23 [dcl.fct]p6:
diff --git a/clang/test/SemaCXX/cxx2b-deducing-this.cpp b/clang/test/SemaCXX/cxx2b-deducing-this.cpp
index b86731c7d7a11..539c8f8700fe7 100644
--- a/clang/test/SemaCXX/cxx2b-deducing-this.cpp
+++ b/clang/test/SemaCXX/cxx2b-deducing-this.cpp
@@ -1170,6 +1170,19 @@ struct S {
 };
 }
 
+namespace GH136472 {
+template<class T>
+struct S {
+  struct Nested {
+      void f(this auto);
+  };
+};
+
+// Test that out-of-line member defination of dependent nested class works
+template<class T>
+void S<T>::Nested::f(this auto) {}
+}
+
 namespace tpl_address {
 
 struct A {

``````````

</details>


https://github.com/llvm/llvm-project/pull/209107