From 6c494adc387f6793f02a55d5a5f811eaa22357b4 Mon Sep 17 00:00:00 2001
From: "Henrik G. Olsson" <h_olsson@apple.com>
Date: Mon, 7 Jul 2025 12:16:42 -0700
Subject: [PATCH] [Modules] Don't const eval VarDecls with dependent type

EvaluateAsInitializer does not support evaluating values with dependent
types. This was previously guarded with a check for the initializer
expression, but it is possible for the VarDecl to have a dependent type
without the initializer having a dependent type, when the initializer is
a specialized template type and the VarDecl has the unspecialized type.
This adds a guard checking for dependence in the VarDecl type as well.
---
 clang/lib/AST/Decl.cpp                        |  3 ++-
 .../var-init-side-effects-templated.cpp       | 20 +++++++++++++++++++
 2 files changed, 22 insertions(+), 1 deletion(-)
 create mode 100644 clang/test/Modules/var-init-side-effects-templated.cpp

diff --git a/clang/lib/AST/Decl.cpp b/clang/lib/AST/Decl.cpp
index e0362245d6ecd..8855d0107daca 100644
--- a/clang/lib/AST/Decl.cpp
+++ b/clang/lib/AST/Decl.cpp
@@ -2450,7 +2450,8 @@ bool VarDecl::hasInitWithSideEffects() const {
     ES->HasSideEffects =
         E->HasSideEffects(getASTContext()) &&
         // We can get a value-dependent initializer during error recovery.
-        (E->isValueDependent() || !evaluateValue());
+        (E->isValueDependent() || getType()->isDependentType() ||
+         !evaluateValue());
     ES->CheckedForSideEffects = true;
   }
   return ES->HasSideEffects;
diff --git a/clang/test/Modules/var-init-side-effects-templated.cpp b/clang/test/Modules/var-init-side-effects-templated.cpp
new file mode 100644
index 0000000000000..542ca270429b6
--- /dev/null
+++ b/clang/test/Modules/var-init-side-effects-templated.cpp
@@ -0,0 +1,20 @@
+// Tests referencing variable with initializer containing side effect across module boundary
+
+// RUN: %clang_cc1 -std=c++20 -emit-module-interface %s -o %t
+
+export module Foo;
+
+export template <class Float>
+struct Wrapper {
+  double value;
+};
+
+export constexpr Wrapper<double> Compute() {
+  return Wrapper<double>{1.0};
+}
+
+export template <typename Float>
+Wrapper<Float> ComputeInFloat() {
+  const Wrapper<Float> a = Compute();
+  return a;
+}