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

[a-tarasyuk]

Fixes #107047
Fixes #49093

[llvmbot]

@llvm/pr-subscribers-clang

Author: Oleksandr T. (a-tarasyuk)

Changes

Fixes #107047
Fixes #49093

---

Full diff: https://github.com/llvm/llvm-project/pull/107786.diff

3 Files Affected:

• (modified) clang/docs/ReleaseNotes.rst (+2-1)
• (modified) clang/lib/Sema/SemaTemplate.cpp (+6)
• (added) clang/test/SemaTemplate/recovery-crash-cxx20.cpp (+32)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index f7c3194c91fa31..f96045c57e7a0d 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -376,8 +376,9 @@ Bug Fixes to C++ Support
 - Fixed a bug in the substitution of empty pack indexing types. (#GH105903)
 - Clang no longer tries to capture non-odr used default arguments of template parameters of generic lambdas (#GH107048)
 - Fixed a bug where defaulted comparison operators would remove ``const`` from base classes. (#GH102588)
-
 - Fix a crash when using ``source_location`` in the trailing return type of a lambda expression. (#GH67134)
+- Fixed an assertion failure when invoking recovery call expressions with explicit attributes
+  and undeclared templates. (#GH107047, #GH49093)
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index 513f83146fb59e..1ec6219bbd6ea8 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -4458,6 +4458,12 @@ ExprResult Sema::BuildTemplateIdExpr(const CXXScopeSpec &SS,
                                   R.getAsSingle<ConceptDecl>(), TemplateArgs);
   }
 
+  if (TemplateArgs && R.getAsSingle<FunctionDecl>()) {
+    if (R.getAsSingle<FunctionDecl>()->getTemplateSpecializationKind() ==
+        TemplateSpecializationKind::TSK_Undeclared)
+      return ExprError();
+  }
+
   // We don't want lookup warnings at this point.
   R.suppressDiagnostics();
 
diff --git a/clang/test/SemaTemplate/recovery-crash-cxx20.cpp b/clang/test/SemaTemplate/recovery-crash-cxx20.cpp
new file mode 100644
index 00000000000000..dd92ddcd36ab02
--- /dev/null
+++ b/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}}
+  };
+}

[erichkeane]

Diag seems reasonable to me now. I want Aaron to take another look (he's sadly out this week, so it'll have to be when he gets back), but I think this seems to make sense here.

[a-tarasyuk]

@erichkeane thanks for the feedback

[cor3ntin]

LGTM. do you need me to merge it for you?

[a-tarasyuk]

@cor3ntin yes, I do. Thanks