fix bug fusing option-type fields

runtime/sam/expr/agg/fuser.go

@@ -60,7 +60,7 @@ func (f *Fuser) fuse(a, b super.Type) super.Type {
 			// First change all fields to optional that are in "a" but not in "b".
 			for k, field := range fields {
 				if _, ok := indexOfField(b.Fields, field.Name); !ok {
-					fields[k].Type = f.sctx.Option(fields[k].Type)
+					fields[k].Type = f.makeOption(fields[k].Type)
 				}
 			}
 			// Now fuse all the fields in "b" that are also in "a" and add the fields
@@ -70,7 +70,7 @@ func (f *Fuser) fuse(a, b super.Type) super.Type {
 				if ok {
 					fields[i].Type = f.fuse(fields[i].Type, field.Type)
 				} else {
-					typ := f.sctx.Option(field.Type)
+					typ := f.makeOption(field.Type)
 					fields = append(fields, super.NewField(field.Name, typ))
 				}
 			}
@@ -144,6 +144,13 @@ func (f *Fuser) fuse(a, b super.Type) super.Type {
 	return f.fusion(union)
 }
 
+func (f *Fuser) makeOption(t super.Type) super.Type {
+	if fusion, ok := t.(*super.TypeFusion); ok {
+		return f.sctx.LookupTypeFusion(f.makeOption(fusion.Type))
+	}
+	return f.sctx.Option(t)
+}
+
 func isAll(t super.Type) bool {
 	_, ok := t.(*super.TypeOfAll)
 	return ok

runtime/ztests/expr/fuser.yaml

@@ -59,3 +59,14 @@ input: &input |
   [{id:1,s:"foo"},{id:2,s:null}]
 
 output: *input
+
+---
+
+spq: fuse | defuse(this)
+
+input: &input |
+  {x:1,y:{z:"foo"}}
+  {x:2,y:{z:"bar",w:true}}
+  {x:3}
+
+output: *input