[clang] Mark ill-formed partial specialization as invalid

[Endilll]

Fixes #89374
Solution suggested by @cor3ntin

[llvmbot]

@llvm/pr-subscribers-clang

Author: Vlad Serebrennikov (Endilll)

Changes

Fixes #89374
Solution suggested by @cor3ntin

---

Full diff: https://github.com/llvm/llvm-project/pull/89536.diff

3 Files Affected:

• (modified) clang/lib/Sema/SemaTemplate.cpp (+2)
• (modified) clang/lib/Sema/SemaTemplateDeduction.cpp (+3)
• (modified) clang/test/SemaCXX/template-specialization.cpp (+28)

diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index d4976f9d0d11d8..2bcbc081750b31 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -9459,6 +9459,7 @@ DeclResult Sema::ActOnClassTemplateSpecialization(
       Diag(TemplateNameLoc, diag::err_partial_spec_fully_specialized)
         << ClassTemplate->getDeclName();
       isPartialSpecialization = false;
+      Invalid = true;
     }
   }
 
@@ -9674,6 +9675,7 @@ DeclResult Sema::ActOnClassTemplateSpecialization(
   if (SkipBody && SkipBody->ShouldSkip)
     return SkipBody->Previous;
 
+  Specialization->setInvalidDecl(Invalid);
   return Specialization;
 }
 
diff --git a/clang/lib/Sema/SemaTemplateDeduction.cpp b/clang/lib/Sema/SemaTemplateDeduction.cpp
index 0b6375001f5326..c3815bca038554 100644
--- a/clang/lib/Sema/SemaTemplateDeduction.cpp
+++ b/clang/lib/Sema/SemaTemplateDeduction.cpp
@@ -1914,6 +1914,9 @@ static TemplateDeductionResult DeduceTemplateArgumentsByTypeMatch(
       if (!S.isCompleteType(Info.getLocation(), A))
         return Result;
 
+      if (getCanonicalRD(A)->isInvalidDecl())
+        return Result;
+
       // Reset the incorrectly deduced argument from above.
       Deduced = DeducedOrig;
 
diff --git a/clang/test/SemaCXX/template-specialization.cpp b/clang/test/SemaCXX/template-specialization.cpp
index 7b26ff9f5c5ba4..eabb84f2e13d3e 100644
--- a/clang/test/SemaCXX/template-specialization.cpp
+++ b/clang/test/SemaCXX/template-specialization.cpp
@@ -52,3 +52,31 @@ void instantiate() {
 }
 
 }
+
+namespace GH89374 {
+
+struct A {};
+
+template <typename Derived>
+struct MatrixBase { // #GH89374-MatrixBase
+  template <typename OtherDerived>
+  Derived &operator=(const MatrixBase<OtherDerived> &); // #GH89374-copy-assignment
+};
+
+template <typename>
+struct solve_retval;
+
+template <typename Rhs>
+struct solve_retval<int> : MatrixBase<solve_retval<Rhs> > {};
+// expected-error@-1 {{partial specialization of 'solve_retval' does not use any of its template parameters}}
+
+void ApproximateChebyshev() {
+  MatrixBase<int> c;
+  c = solve_retval<int>();
+  // expected-error@-1 {{no viable overloaded '='}}
+  //   expected-note@#GH89374-copy-assignment {{candidate template ignored: could not match 'MatrixBase' against 'solve_retval'}}
+  //   expected-note@#GH89374-MatrixBase {{candidate function (the implicit copy assignment operator) not viable: no known conversion from 'solve_retval<int>' to 'const MatrixBase<int>' for 1st argument}}
+  //   expected-note@#GH89374-MatrixBase {{candidate function (the implicit move assignment operator) not viable: no known conversion from 'solve_retval<int>' to 'MatrixBase<int>' for 1st argument}}
+}
+
+} // namespace GH89374

[erichkeane]

Release note, else LGTM.