[Clang] prevent recovery call expression from proceeding with explicit attributes and undeclared templates

Author: a-tarasyuk

clang/docs/ReleaseNotes.rst

@@ -386,7 +386,8 @@ Bug Fixes to C++ Support
 - Fixed a crash in the typo correction of an invalid CTAD guide. (#GH107887)
 - Fixed a crash when clang tries to subtitute parameter pack while retaining the parameter
   pack. #GH63819, #GH107560
-
+- Fixed an assertion failure when invoking recovery call expressions with explicit attributes
+  and undeclared templates. (#GH107047, #GH49093)
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^

clang/lib/Sema/SemaTemplate.cpp

@@ -4460,6 +4460,11 @@ ExprResult Sema::BuildTemplateIdExpr(const CXXScopeSpec &SS,
                                   R.getAsSingle<ConceptDecl>(), TemplateArgs);
   }
 
+  if (TemplateArgs && R.getAsSingle<FunctionDecl>() &&
+      R.getAsSingle<FunctionDecl>()->getTemplateSpecializationKind() ==
+          TemplateSpecializationKind::TSK_Undeclared)
+    return ExprError();
+
   // We don't want lookup warnings at this point.
   R.suppressDiagnostics();
 

clang/test/SemaTemplate/recovery-crash-cxx20.cpp

@@ -0,0 +1,32 @@
+// RUN: %clang_cc1 -fsyntax-only -verify -std=c++20 %s
+
+namespace GH49093 {
+  class B {
+  public:
+    static int a() { return 0; } // expected-note {{member is declared here}}
+    decltype(a< 0 >(0)) test;    // expected-error {{member 'a' used before its declaration}}
+  };
+
+  struct C {
+      static int a() { return 0; } // expected-note {{member is declared here}}
+      decltype(a < 0 > (0)) test;  // expected-error {{member 'a' used before its declaration}}
+  };
+
+  void test_is_bool(bool t) {}
+  void test_is_bool(int t) {}
+
+  int main() {
+    B b;
+    test_is_bool(b.test);
+
+    C c;
+    test_is_bool(c.test);
+  }
+}
+
+namespace GH107047 {
+  struct A {
+    static constexpr auto test() { return 1; } // expected-note {{member is declared here}}
+    static constexpr int s = test< 1 >();      // expected-error {{member 'test' used before its declaration}}
+  };
+}