From fd024b9bf97b11abbac4f1926f3453b098e3b66a Mon Sep 17 00:00:00 2001
From: Steven McCanne <steve@mccanne.com>
Date: Sat, 2 May 2026 07:28:44 -0700
Subject: [PATCH] fix bug fusing option-type fields

With the new design for option types, the fuser needs to fuse
optional fields such that the option type of the field is pushed
into the field's fusion type so we have fusion(...|none) instead of
none|fusion(...).  This problem was causing upcast to fail on
such patterns.  We've added test coverage to catch this.
---
 runtime/sam/expr/agg/fuser.go  | 11 +++++++++--
 runtime/ztests/expr/fuser.yaml | 11 +++++++++++
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/runtime/sam/expr/agg/fuser.go b/runtime/sam/expr/agg/fuser.go
index 9d3afb7f6..0a52eb41e 100644
--- a/runtime/sam/expr/agg/fuser.go
+++ b/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
diff --git a/runtime/ztests/expr/fuser.yaml b/runtime/ztests/expr/fuser.yaml
index 908c4a86e..a13161e0c 100644
--- a/runtime/ztests/expr/fuser.yaml
+++ b/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