From 4fd4f57ef9212c847ee05e034aed3bf7c59cb3cc Mon Sep 17 00:00:00 2001
From: zebullax <zebullax@gmail.com>
Date: Tue, 11 Nov 2025 11:24:11 +0900
Subject: [PATCH] Check against subst failure ouside of imm context (#206)

Signed-off-by: zebullax <zebullax@gmail.com>
---
 clang/lib/AST/ExprConstantMeta.cpp | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/clang/lib/AST/ExprConstantMeta.cpp b/clang/lib/AST/ExprConstantMeta.cpp
index 78d0e8ad2125..2a1b752589b0 100644
--- a/clang/lib/AST/ExprConstantMeta.cpp
+++ b/clang/lib/AST/ExprConstantMeta.cpp
@@ -2985,17 +2985,21 @@ bool substitute(APValue &Result, ASTContext &C, MetaActions &Meta,
                const_cast<Type *>(TSpecDecl->getTypeForDecl()));
     //C.recordCachedSubstitution(SubstitutionHash, RV);
     return SetAndSucceed(Result, RV);
-  } else if (auto *TATD = dyn_cast<TypeAliasTemplateDecl>(TDecl)) {
+  }
+  if (auto *TATD = dyn_cast<TypeAliasTemplateDecl>(TDecl)) {
     TArgs.clear();
     expandTemplateArgPacks(ExpandedTArgs, TArgs);
 
     QualType QT = Meta.Substitute(TATD, TArgs, Range.getBegin());
-    assert(!QT.isNull() && "substitution failed after validating arguments?");
-
+    if(QT.isNull()) {
+      // substitution failed after validating arguments
+      return true;
+    }
     APValue RV = makeReflection(QT);
     //C.recordCachedSubstitution(SubstitutionHash, RV);
     return SetAndSucceed(Result, makeReflection(QT));
-  } else if (auto *FTD = dyn_cast<FunctionTemplateDecl>(TDecl)) {
+  }
+  if (auto *FTD = dyn_cast<FunctionTemplateDecl>(TDecl)) {
     FunctionDecl *Spec = Meta.Substitute(FTD, ExpandedTArgs, Range.getBegin());
     assert(Spec && "substitution failed after validating arguments?");
 
@@ -3007,7 +3011,8 @@ bool substitute(APValue &Result, ASTContext &C, MetaActions &Meta,
     APValue RV = makeReflection(Spec);
     //C.recordCachedSubstitution(SubstitutionHash, RV);
     return SetAndSucceed(Result, RV);
-  } else if (auto *VTD = dyn_cast<VarTemplateDecl>(TDecl)) {
+  }
+  if (auto *VTD = dyn_cast<VarTemplateDecl>(TDecl)) {
     TArgs.clear();
     expandTemplateArgPacks(ExpandedTArgs, TArgs);
 
@@ -3017,7 +3022,8 @@ bool substitute(APValue &Result, ASTContext &C, MetaActions &Meta,
     APValue RV = makeReflection(Spec);
     //C.recordCachedSubstitution(SubstitutionHash, RV);
     return SetAndSucceed(Result, makeReflection(Spec));
-  } else if (auto *CD = dyn_cast<ConceptDecl>(TDecl)) {
+  }
+  if (auto *CD = dyn_cast<ConceptDecl>(TDecl)) {
     TArgs.clear();
     expandTemplateArgPacks(ExpandedTArgs, TArgs);