Fix `extension` incorrectly interacting with `equality` and `type-coercion` constraints (#7578)

* fix problem

* cleanup comment

* format code

* make change more restrictive

* format code

* push logic update

* format code

* push test fix

* make test more general

---------

Co-authored-by: slangbot <186143334+slangbot@users.noreply.github.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/source/slang/slang-check-constraint.cpp b/source/slang/slang-check-constraint.cpp
index 7c55c440c..7c6f8929a 100644
--- a/source/slang/slang-check-constraint.cpp
+++ b/source/slang/slang-check-constraint.cpp
@@ -363,6 +363,7 @@ DeclRef<Decl> SemanticsVisitor::trySolveConstraintSystem(
         ValUnificationContext unificationContext;
         unificationContext.optionalConstraint =
             constraintDeclRef.getDecl()->hasModifier<OptionalConstraintModifier>();
+        unificationContext.equalityConstraint = constraintDeclRef.getDecl()->isEqualityConstraint;
         if (!TryUnifyTypes(
                 *system,
                 unificationContext,
@@ -492,6 +493,8 @@ DeclRef<Decl> SemanticsVisitor::trySolveConstraintSystem(
                 {
                     if (c.isOptional)
                         joinType = type;
+                    else if (c.isEquality)
+                        joinType = type;
                     else
                         // failure!
                         return DeclRef<Decl>();
@@ -970,6 +973,7 @@ bool SemanticsVisitor::TryUnifyTypeParam(
     constraint.val = type;
     constraint.isUsedAsLValue = type.isLeftValue;
     constraint.isOptional = unificationContext.optionalConstraint;
+    constraint.isEquality = unificationContext.equalityConstraint;
     constraints.constraints.add(constraint);
 
     return true;