[clang] [Clang][Sema] fix deducing auto& from const int in template parameters is impossible in partial specializations (PR #79733)

[Qizhi Hu via cfe-commits]

https://github.com/jcsxky updated 
https://github.com/llvm/llvm-project/pull/79733

>From 9834d065580a668f94f74adaf8507ca672e9118f Mon Sep 17 00:00:00 2001
From: huqizhi <huqi...@feysh.com>
Date: Sun, 28 Jan 2024 15:12:01 +0800
Subject: [PATCH] [Clang][Sema] fix deducing auto& from const int in template
 parameters is impossible in partial specializations

---
 clang/lib/Sema/SemaTemplateDeduction.cpp |  1 +
 clang/test/SemaTemplate/PR77189.cpp      | 22 ++++++++++++++++++++++
 2 files changed, 23 insertions(+)
 create mode 100644 clang/test/SemaTemplate/PR77189.cpp

diff --git a/clang/lib/Sema/SemaTemplateDeduction.cpp 
b/clang/lib/Sema/SemaTemplateDeduction.cpp
index 25e58f7bdd953d1..f08577febcd3e80 100644
--- a/clang/lib/Sema/SemaTemplateDeduction.cpp
+++ b/clang/lib/Sema/SemaTemplateDeduction.cpp
@@ -649,6 +649,7 @@ static bool IsPossiblyOpaquelyQualifiedTypeInternal(const 
Type *T) {
   case Type::PackIndexing:
   case Type::UnresolvedUsing:
   case Type::TemplateTypeParm:
+  case Type::Auto:
     return true;
 
   case Type::ConstantArray:
diff --git a/clang/test/SemaTemplate/PR77189.cpp 
b/clang/test/SemaTemplate/PR77189.cpp
new file mode 100644
index 000000000000000..1e9cc7984163c06
--- /dev/null
+++ b/clang/test/SemaTemplate/PR77189.cpp
@@ -0,0 +1,22 @@
+// RUN: %clang_cc1 -fsyntax-only -std=c++17 -verify %s
+// RUN: %clang_cc1 -fsyntax-only -std=c++20 -verify %s
+// expected-no-diagnostics
+
+struct false_type {
+       static constexpr bool value = false;
+};
+
+struct true_type {
+       static constexpr bool value = true;
+};
+
+template <auto& Value, int>
+struct test : false_type {};
+
+template <auto& Value>
+struct test<Value, 0> : true_type {};
+
+int main() {
+    static constexpr int v = 42;
+    static_assert(test<v, 0>::value);
+}

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