From 4d33a8dfcf67e970ea4d150d514b27de02e79aee Mon Sep 17 00:00:00 2001
From: Saar Raz <saar@raz.email>
Date: Thu, 23 Jan 2020 23:24:56 +0200
Subject: [PATCH] [Concepts] Add ExpressionEvaluationContexts to instantiation
 of constraints

Proper ExpressionEvaluationContext were not being entered when instantiating constraint
expressions, which caused assertion failures in certain cases, including bug #44614.
---
 clang/lib/Sema/SemaTemplateInstantiateDecl.cpp          |  8 ++++++++
 clang/test/SemaTemplate/instantiate-requires-clause.cpp | 12 ++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
index 8fd7491c45e..92f6e0dc1c9 100755
--- a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -1848,6 +1848,8 @@ Decl *TemplateDeclInstantiator::VisitFunctionDecl(
   // FIXME: Concepts: Do not substitute into constraint expressions
   Expr *TrailingRequiresClause = D->getTrailingRequiresClause();
   if (TrailingRequiresClause) {
+    EnterExpressionEvaluationContext ConstantEvaluated(
+        SemaRef, Sema::ExpressionEvaluationContext::ConstantEvaluated);
     ExprResult SubstRC = SemaRef.SubstExpr(TrailingRequiresClause,
                                            TemplateArgs);
     if (SubstRC.isInvalid())
@@ -2186,6 +2188,8 @@ Decl *TemplateDeclInstantiator::VisitCXXMethodDecl(
   // FIXME: Concepts: Do not substitute into constraint expressions
   Expr *TrailingRequiresClause = D->getTrailingRequiresClause();
   if (TrailingRequiresClause) {
+    EnterExpressionEvaluationContext ConstantEvaluated(
+        SemaRef, Sema::ExpressionEvaluationContext::ConstantEvaluated);
     ExprResult SubstRC = SemaRef.SubstExpr(TrailingRequiresClause,
                                            TemplateArgs);
     if (SubstRC.isInvalid())
@@ -2525,6 +2529,8 @@ Decl *TemplateDeclInstantiator::VisitTemplateTypeParmDecl(
     TemplateArgumentListInfo InstArgs;
 
     if (TemplArgInfo) {
+      EnterExpressionEvaluationContext ConstantEvaluated(
+        SemaRef, Sema::ExpressionEvaluationContext::ConstantEvaluated);
       InstArgs.setLAngleLoc(TemplArgInfo->LAngleLoc);
       InstArgs.setRAngleLoc(TemplArgInfo->RAngleLoc);
       if (SemaRef.Subst(TemplArgInfo->getTemplateArgs(),
@@ -3729,6 +3735,8 @@ TemplateDeclInstantiator::SubstTemplateParams(TemplateParameterList *L) {
   // checking satisfaction.
   Expr *InstRequiresClause = nullptr;
   if (Expr *E = L->getRequiresClause()) {
+    EnterExpressionEvaluationContext ConstantEvaluated(
+        SemaRef, Sema::ExpressionEvaluationContext::ConstantEvaluated);
     ExprResult Res = SemaRef.SubstExpr(E, TemplateArgs);
     if (Res.isInvalid() || !Res.isUsable()) {
       return nullptr;
diff --git a/clang/test/SemaTemplate/instantiate-requires-clause.cpp b/clang/test/SemaTemplate/instantiate-requires-clause.cpp
index 04b595717e6..3b7dc3ddd74 100644
--- a/clang/test/SemaTemplate/instantiate-requires-clause.cpp
+++ b/clang/test/SemaTemplate/instantiate-requires-clause.cpp
@@ -39,3 +39,15 @@ struct S {
 };
 
 static_assert(S<void>::f(1));
+
+constexpr auto value = 0;
+
+template<typename T>
+struct S2 {
+  template<typename = void> requires(value, true)
+  static constexpr auto f() requires(value, true) {
+  }
+};
+
+static_assert((S2<int>::f(), true));
+
-- 
2.11.0