[clang] Mark ill-formed partial specialization as invalid (#89536)

Fixes #89374
Solution suggested by @cor3ntin

Author: Endilll

clang/docs/ReleaseNotes.rst

@@ -415,6 +415,9 @@ Bug Fixes in This Version
   operator.
   Fixes (#GH83267).
 
+- Fix crash on ill-formed partial specialization with CRTP.
+  Fixes (#GH89374).
+
 - Clang now correctly generates overloads for bit-precise integer types for
   builtin operators in C++. Fixes #GH82998.
 

clang/lib/Sema/SemaTemplate.cpp

@@ -9460,6 +9460,7 @@ DeclResult Sema::ActOnClassTemplateSpecialization(
       Diag(TemplateNameLoc, diag::err_partial_spec_fully_specialized)
         << ClassTemplate->getDeclName();
       isPartialSpecialization = false;
+      Invalid = true;
     }
   }
 
@@ -9675,6 +9676,7 @@ DeclResult Sema::ActOnClassTemplateSpecialization(
   if (SkipBody && SkipBody->ShouldSkip)
     return SkipBody->Previous;
 
+  Specialization->setInvalidDecl(Invalid);
   return Specialization;
 }
 

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;
 

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