[clang] [Clang] Fix handling of references to variable templates with an empty argument list (PR #191154)

[Corentin Jabot via cfe-commits]

https://github.com/cor3ntin updated https://github.com/llvm/llvm-project/pull/191154

>From e05e87da59ac0cce0d9590fc006f362ed3136f5b Mon Sep 17 00:00:00 2001
From: Corentin Jabot <corentinjabot at gmail.com>
Date: Thu, 9 Apr 2026 12:10:42 +0200
Subject: [PATCH 1/3] [Clang] Fix handling of references to variable templates
 with an empty argument list

In some cases they were treated as having no argument list at all.

Fixes #191016.
---
 clang/docs/ReleaseNotes.rst          |  1 +
 clang/include/clang/AST/ExprCXX.h    |  8 +++++---
 clang/test/SemaTemplate/concepts.cpp | 11 +++++++++++
 3 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 2da7175b51ea3..a72821bf970f1 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -426,6 +426,7 @@ Bug Fixes to C++ Support
   template parameters when one of its parameters is also a pack. (#GH181166)
 - Fixed a crash when a default argument is passed to an explicit object parameter. (#GH176639)
 - Fixed an alias template CTAD crash.
+- Fix handling of ``Var<>`` when refering to a static member variable template. (#GH191016)
 - Fixed a crash when diagnosing an invalid static member function with an explicit object parameter (#GH177741)
 - Fixed a crash when instantiating an invalid out-of-line static data member definition in a local class. (#GH176152)
 - Fixed a crash when pack expansions are used as arguments for non-pack parameters of built-in templates. (#GH180307)
diff --git a/clang/include/clang/AST/ExprCXX.h b/clang/include/clang/AST/ExprCXX.h
index c40cd929b7408..10c0f2ba6c44b 100644
--- a/clang/include/clang/AST/ExprCXX.h
+++ b/clang/include/clang/AST/ExprCXX.h
@@ -3281,12 +3281,14 @@ class OverloadExpr : public Expr {
   bool hasExplicitTemplateArgs() const {
     if (!hasTemplateKWAndArgsInfo())
       return false;
+    if (getLAngleLoc().isValid())
+      return true;
     // FIXME: deduced function types can have "hidden" args and no <
     // investigate that further, but ultimately maybe we want to model concepts
     // reference with another kind of expression.
-    return (isConceptReference() || isVarDeclReference())
-               ? getTrailingASTTemplateKWAndArgsInfo()->NumTemplateArgs
-               : getLAngleLoc().isValid();
+    if (isConceptReference() || isVarDeclReference())
+      return getTrailingASTTemplateKWAndArgsInfo()->NumTemplateArgs;
+    return false;
   }
 
   bool isConceptReference() const {
diff --git a/clang/test/SemaTemplate/concepts.cpp b/clang/test/SemaTemplate/concepts.cpp
index 429df756c1c4f..ac80d16b4ccf8 100644
--- a/clang/test/SemaTemplate/concepts.cpp
+++ b/clang/test/SemaTemplate/concepts.cpp
@@ -1824,3 +1824,14 @@ namespace GH176402 {
     recursiveLambda(recursiveLambda, 5);
   }
 }
+namespace GH191016 {
+  template <typename T = int>
+  struct S {
+    template <typename Args = int>
+    constexpr static bool P = true;
+    template <typename... Args>
+    constexpr static bool Q = true;
+    S() requires P<> && Q<> {}
+  };
+  void test(){ S<int> s; }
+}

>From a7df3c347d863e097713e1ac9d3b796381b4546b Mon Sep 17 00:00:00 2001
From: Corentin Jabot <corentinjabot at gmail.com>
Date: Thu, 9 Apr 2026 13:41:46 +0200
Subject: [PATCH 2/3] remove stale comment

---
 clang/include/clang/AST/ExprCXX.h | 10 ++--------
 1 file changed, 2 insertions(+), 8 deletions(-)

diff --git a/clang/include/clang/AST/ExprCXX.h b/clang/include/clang/AST/ExprCXX.h
index 10c0f2ba6c44b..948f18b31a5fc 100644
--- a/clang/include/clang/AST/ExprCXX.h
+++ b/clang/include/clang/AST/ExprCXX.h
@@ -3279,16 +3279,10 @@ class OverloadExpr : public Expr {
 
   /// Determines whether this expression had explicit template arguments.
   bool hasExplicitTemplateArgs() const {
-    if (!hasTemplateKWAndArgsInfo())
-      return false;
     if (getLAngleLoc().isValid())
       return true;
-    // FIXME: deduced function types can have "hidden" args and no <
-    // investigate that further, but ultimately maybe we want to model concepts
-    // reference with another kind of expression.
-    if (isConceptReference() || isVarDeclReference())
-      return getTrailingASTTemplateKWAndArgsInfo()->NumTemplateArgs;
-    return false;
+    return hasTemplateKWAndArgsInfo() &&
+           getTrailingASTTemplateKWAndArgsInfo()->NumTemplateArgs;
   }
 
   bool isConceptReference() const {

>From 8ccca6a87164b89ef7934ccb53b32a1bad5b6415 Mon Sep 17 00:00:00 2001
From: Corentin Jabot <corentinjabot at gmail.com>
Date: Thu, 9 Apr 2026 14:46:25 +0200
Subject: [PATCH 3/3] remove release note

---
 clang/docs/ReleaseNotes.rst | 1 -
 1 file changed, 1 deletion(-)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index a72821bf970f1..2da7175b51ea3 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -426,7 +426,6 @@ Bug Fixes to C++ Support
   template parameters when one of its parameters is also a pack. (#GH181166)
 - Fixed a crash when a default argument is passed to an explicit object parameter. (#GH176639)
 - Fixed an alias template CTAD crash.
-- Fix handling of ``Var<>`` when refering to a static member variable template. (#GH191016)
 - Fixed a crash when diagnosing an invalid static member function with an explicit object parameter (#GH177741)
 - Fixed a crash when instantiating an invalid out-of-line static data member definition in a local class. (#GH176152)
 - Fixed a crash when pack expansions are used as arguments for non-pack parameters of built-in templates. (#GH180307)