[clang] [Clang] Adjust NTTP depths in IsAtLeastAsConstrained (PR #209445)

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<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Younan Zhang (zyn0217)

<details>
<summary>Changes</summary>

The default transform for NTTP, which is no-op, doesn't help if we need to adjust their depths when comparing constraints.

Fixes https://github.com/llvm/llvm-project/issues/182671

---
Full diff: https://github.com/llvm/llvm-project/pull/209445.diff


3 Files Affected:

- (modified) clang/docs/ReleaseNotes.md (+1) 
- (modified) clang/lib/Sema/SemaConcept.cpp (+24) 
- (modified) clang/test/SemaCXX/concepts-subsumption.cpp (+18-1) 


``````````diff
diff --git a/clang/docs/ReleaseNotes.md b/clang/docs/ReleaseNotes.md
index 9063e54b3e692..06fdb04ab95db 100644
--- a/clang/docs/ReleaseNotes.md
+++ b/clang/docs/ReleaseNotes.md
@@ -778,6 +778,7 @@ latest release, please see the [Clang Web Site](https://clang.llvm.org) or the
 - Fixed a preprocessor crash in `__has_cpp_attribute` on incomplete scoped attributes. (#GH178098)
 - Fixes an assertion failure when evaluating `__underlying_type` on enum redeclarations. (#GH177943)
 - Fixed an assertion failure caused by nested macro expansion during header-name lexing (`__has_embed(__has_include)`). (#GH178635)
+- Fixed a constraint comparison bug in partial ordering. (#GH182671)
 - Clang now outputs relative paths of embeds for dependency output. (#GH161950)
 - Fix the result type of a binary operation where both operands are 'void' l-values. (#GH111300)
 - Fixed an assertion failure when evaluating `_Countof` on invalid `void`-typed operands. (#GH180893)
diff --git a/clang/lib/Sema/SemaConcept.cpp b/clang/lib/Sema/SemaConcept.cpp
index 476910a9db528..99b4e61c5e0a1 100644
--- a/clang/lib/Sema/SemaConcept.cpp
+++ b/clang/lib/Sema/SemaConcept.cpp
@@ -276,6 +276,30 @@ class AdjustConstraints : public TreeTransform<AdjustConstraints> {
       return false;
     return true;
   }
+
+  ExprResult TransformDeclRefExpr(DeclRefExpr *E) {
+    NonTypeTemplateParmDecl *NTTP = dyn_cast<NonTypeTemplateParmDecl>(E->getDecl());
+    if (!NTTP)
+      return inherited::TransformDeclRefExpr(E);
+
+    assert(E->getTemplateArgs() == nullptr &&
+           "Template arguments for NTTP decl?");
+    auto *TSI = inherited::TransformType(NTTP->getTypeSourceInfo());
+    if (!TSI)
+      return ExprError();
+
+    auto *D = NonTypeTemplateParmDecl::Create(
+        SemaRef.getASTContext(), NTTP->getDeclContext(),
+        NTTP->getInnerLocStart(), NTTP->getLocation(),
+        NTTP->getDepth() + TemplateDepth, NTTP->getPosition(),
+        NTTP->getIdentifier(), TSI->getType(), NTTP->isParameterPack(), TSI);
+
+    return DeclRefExpr::Create(
+        SemaRef.getASTContext(), E->getQualifierLoc(),
+        E->getTemplateKeywordLoc(), D, E->refersToEnclosingVariableOrCapture(),
+        E->getNameInfo(), TSI->getType(), E->getValueKind(), D,
+        /*TemplateArgs=*/nullptr, E->isNonOdrUse());
+  }
 };
 } // namespace
 
diff --git a/clang/test/SemaCXX/concepts-subsumption.cpp b/clang/test/SemaCXX/concepts-subsumption.cpp
index d9d5535e532f4..d00a8b973cb91 100644
--- a/clang/test/SemaCXX/concepts-subsumption.cpp
+++ b/clang/test/SemaCXX/concepts-subsumption.cpp
@@ -1,5 +1,5 @@
 // RUN: %clang_cc1 -fsyntax-only -verify -std=c++20 %s
-// expected-no-diagnostics
+
 namespace A {
 template <typename T>
 concept C = true;
@@ -32,6 +32,23 @@ constexpr int f() { return 1; }
 static_assert(f<int>() == 0);
 }
 
+namespace GH182671 {
+
+template<int N> concept Positive = N > 0;
+template<int N> requires Positive<N> struct A {};
+// expected-note at -1 {{'A' declared here}}
+template<template<int N> requires Positive<N> typename T> struct Wrapper {};
+using X = Wrapper<A>;
+
+template<template<int N> requires Positive<N + 1> typename T> struct Wrapper2 {};
+// expected-note at -1 {{'T' declared here}}
+
+// FIXME: The diagnostics are not great
+using Y = Wrapper2<A>;
+// expected-error at -1 {{template template argument 'A' is more constrained than template template parameter 'T'}}
+
+}
+
 namespace GH122581 {
 // Test that producing a Conjunctive Normal Form
 // does not blow up exponentially.

``````````

</details>


https://github.com/llvm/llvm-project/pull/209445