Address comments and poke the CI

Author: zyn0217

clang/lib/Sema/SemaTemplateInstantiate.cpp

@@ -345,15 +345,23 @@ MultiLevelTemplateArgumentList Sema::getTemplateInstantiationArgs(
   using namespace TemplateInstArgsHelpers;
   const Decl *CurDecl = ND;
 
-  if (!ND)
+  if (!CurDecl)
     CurDecl = Decl::castFromDeclContext(DC);
 
   if (Innermost) {
     Result.addOuterTemplateArguments(const_cast<NamedDecl *>(ND),
                                      Innermost->asArray(), Final);
-    if (CurDecl->getDeclContext()->isFileContext())
-      if (const auto *TTP = dyn_cast<TemplateTemplateParmDecl>(CurDecl))
-        HandleDefaultTempArgIntoTempTempParam(TTP, Result);
+    // Populate placeholder template arguments for TemplateTemplateParmDecls
+    // that live in a file-scope DeclContext. This is essential for the case
+    // e.g.
+    //
+    // template <class> concept Concept = false;
+    // template <template <Concept C> class T> void foo(T<int>)
+    //
+    // where parameter C has a depth of 1 but the substituting argument `int`
+    // has a depth of 0.
+    if (const auto *TTP = dyn_cast<TemplateTemplateParmDecl>(CurDecl))
+      HandleDefaultTempArgIntoTempTempParam(TTP, Result);
     CurDecl = Response::UseNextDecl(CurDecl).NextDecl;
   }
 
@@ -384,10 +392,8 @@ MultiLevelTemplateArgumentList Sema::getTemplateInstantiationArgs(
       R = Response::ChangeDecl(CTD->getLexicalDeclContext());
     } else if (!isa<DeclContext>(CurDecl)) {
       R = Response::DontClearRelativeToPrimaryNextDecl(CurDecl);
-      if (CurDecl->getDeclContext()->isTranslationUnit()) {
-        if (const auto *TTP = dyn_cast<TemplateTemplateParmDecl>(CurDecl)) {
-          R = HandleDefaultTempArgIntoTempTempParam(TTP, Result);
-        }
+      if (const auto *TTP = dyn_cast<TemplateTemplateParmDecl>(CurDecl)) {
+        R = HandleDefaultTempArgIntoTempTempParam(TTP, Result);
       }
     } else {
       R = HandleGenericDeclContext(CurDecl);

clang/test/CXX/temp/temp.arg/temp.arg.template/p3-2a.cpp

@@ -68,6 +68,8 @@ concept True = true;
 template<typename T>
 concept False = false; // #False
 
+template <class> struct S {};
+
 template<template<True T> typename Wrapper>
 using Test = Wrapper<int>;
 
@@ -77,10 +79,12 @@ using Test = Wrapper<int>; // expected-error {{constraints not satisfied for tem
 // expected-note@#TTP-Wrapper {{'int' does not satisfy 'False'}}
 // expected-note@#False {{evaluated to false}}
 
-template <template<False> typename T> // #TTP-foo
-void foo(T<int>); // expected-error {{constraints not satisfied for template template parameter 'T' [with $0 = int]}}
+template <typename U, template<False> typename T>
+void foo(T<U>); // #foo
 
-// expected-note@#TTP-foo {{'int' does not satisfy 'False'}}
-// expected-note@#False {{evaluated to false}}
+void bar() {
+  foo<int>(S<int>{}); // expected-error {{no matching function for call to 'foo'}}
+  // expected-note@#foo {{substitution failure [with U = int]: constraints not satisfied for template template parameter 'T' [with $0 = int]}}
+}
 
 }