[llvm-branch-commits] [clang] [clang] Backport: allow canonicalizing assumed template names (PR #183823)

[via llvm-branch-commits]

https://github.com/dyung updated https://github.com/llvm/llvm-project/pull/183823

>From cb79aaed35b08a38846c5a09448870c673a88b43 Mon Sep 17 00:00:00 2001
From: Matheus Izvekov <mizvekov at gmail.com>
Date: Tue, 24 Feb 2026 21:51:13 -0300
Subject: [PATCH] [clang] Backport: allow canonicalizing assumed template names

Assumed template names are part of error recovery and encode just a
declaration name, making them always canonical. This patch allows
them to be canonicalized, which is trivial.

Backport from #183222

Fixes #183075
---
 clang/lib/AST/ASTContext.cpp         |  7 +++++--
 clang/test/SemaTemplate/GH183075.cpp | 13 +++++++++++++
 2 files changed, 18 insertions(+), 2 deletions(-)
 create mode 100644 clang/test/SemaTemplate/GH183075.cpp

diff --git a/clang/lib/AST/ASTContext.cpp b/clang/lib/AST/ASTContext.cpp
index f52470a4d7458..100e37c131ef2 100644
--- a/clang/lib/AST/ASTContext.cpp
+++ b/clang/lib/AST/ASTContext.cpp
@@ -7244,9 +7244,12 @@ TemplateName ASTContext::getCanonicalTemplateName(TemplateName Name,
     return TemplateName(cast<TemplateDecl>(Template->getCanonicalDecl()));
   }
 
-  case TemplateName::OverloadedTemplate:
   case TemplateName::AssumedTemplate:
-    llvm_unreachable("cannot canonicalize unresolved template");
+    // An assumed template is just a name, so it is already canonical.
+    return Name;
+
+  case TemplateName::OverloadedTemplate:
+    llvm_unreachable("cannot canonicalize overloaded template");
 
   case TemplateName::DependentTemplate: {
     DependentTemplateName *DTN = Name.getAsDependentTemplateName();
diff --git a/clang/test/SemaTemplate/GH183075.cpp b/clang/test/SemaTemplate/GH183075.cpp
new file mode 100644
index 0000000000000..a9aa7d7a2157a
--- /dev/null
+++ b/clang/test/SemaTemplate/GH183075.cpp
@@ -0,0 +1,13 @@
+// RUN: %clang_cc1 -verify %s
+
+int bar; // #bar
+
+int foo()
+{
+  // FIXME: Bad error recovery.
+  (void)(baz<> + baz<>);
+  // expected-error at -1 2{{use of undeclared identifier 'baz'; did you mean 'bar'?}}
+  // expected-note@#bar 2{{'bar' declared here}}
+  // expected-error at -3 2{{'bar' is expected to be a non-type template, but instantiated to a class template}}
+  // expected-note@#bar 2{{class template declared here}}
+}