Fixup field lookup from a member function defined in an extension

This fixes item 2 in #361

Modifies existing extension-multi-interface.slang test case to cover the additional scenario.

2 files changed, 16 insertions, 2 deletions

diff --git a/source/slang/lookup.cpp b/source/slang/lookup.cpp
index 376d9bd6d..19503d63f 100644
--- a/source/slang/lookup.cpp
+++ b/source/slang/lookup.cpp
@@ -345,7 +345,19 @@ void DoLookupImpl(
 
             // Now perform "local" lookup in the context of the container,
             // as if we were looking up a member directly.
-            //
+            
+            // if we are currently in an extension decl, perform local lookup
+            // in the target decl we are extending
+            if (auto extDeclRef = containerDeclRef.As<ExtensionDecl>())
+            {
+                if (auto targetDeclRef = extDeclRef.getDecl()->targetType->AsDeclRefType())
+                {
+                    if (auto aggDeclRef = targetDeclRef->declRef.As<AggTypeDecl>())
+                    {
+                        containerDeclRef = extDeclRef.Substitute(aggDeclRef);
+                    }
+                }
+            }
             DoLocalLookupImpl(
                 session,
                 name, containerDeclRef, request, result, breadcrumbs);
diff --git a/tests/compute/extension-multi-interface.slang b/tests/compute/extension-multi-interface.slang
index 6cc88f87c..c5136fb3c 100644
--- a/tests/compute/extension-multi-interface.slang
+++ b/tests/compute/extension-multi-interface.slang
@@ -21,6 +21,7 @@ interface IAddAndSub
 
 struct Simple : IAdd
 {
+    float base;
     float addf(float u, float v)
     {
         return u+v;
@@ -31,7 +32,7 @@ __extension Simple : ISub, IAddAndSub
 {
     float subf(float u, float v)
     {
-        return u-v;
+        return base+u-v;
     }
 };
 
@@ -44,6 +45,7 @@ float testAddSub<T:IAddAndSub>(T t)
 void computeMain(uint3 dispatchThreadID : SV_DispatchThreadID)
 {
     Simple s;
+    s.base = 0.0;
 	float outVal = testAddSub(s);
 	outputBuffer[dispatchThreadID.x] = outVal;
 }
\ No newline at end of file