From a59cf38c94700bd616ce1f9c1a15617219e50beb Mon Sep 17 00:00:00 2001
From: Noah Treuhaft <noah.treuhaft@gmail.com>
Date: Wed, 10 Jun 2026 15:03:01 -0400
Subject: [PATCH] fix bug in super.Context.LookupByValue by copying parameter

LookupByValue caches its parameter, a byte slice, in the context, so if
the backing array is later modified through another reference, the
cached value changes.  This can cause LookupTypeValue to return an
incorrect result since it returns these cached values.  Fix this in
LookupByValue by caching a copy of the paramter.
---
 context.go      |  2 +-
 context_test.go | 15 +++++++++++++++
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/context.go b/context.go
index c48f8230cd..a0983191af 100644
--- a/context.go
+++ b/context.go
@@ -386,7 +386,7 @@ func (c *Context) LookupByValue(tv scode.Bytes) (Type, error) {
 	if rest == nil {
 		return nil, errors.New("bad type value encoding")
 	}
-	c.toValue[typ] = tv
+	c.toValue[typ] = slices.Clone(tv)
 	c.toType[string(tv)] = typ
 	return typ, nil
 }
diff --git a/context_test.go b/context_test.go
index 0548b2179d..f98e1e6ebf 100644
--- a/context_test.go
+++ b/context_test.go
@@ -8,6 +8,21 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
+func TestContextLookupByValueAndLookupTypeValue(t *testing.T) {
+	sctx := super.NewContext()
+	recType := sctx.MustLookupTypeRecord(nil)
+
+	tv := super.EncodeTypeValue(recType)
+	typ, err := sctx.LookupByValue(tv)
+	require.NoError(t, err)
+	assert.Equal(t, recType, typ)
+
+	// Overwriting tv should not affect sctx's cached type value for recType.
+	super.AppendTypeValue(tv[:0], super.TypeNull)
+	val := sctx.LookupTypeValue(recType)
+	assert.Exactly(t, super.EncodeTypeValue(recType), val.Bytes())
+}
+
 func TestContextLookupTypeNamedErrors(t *testing.T) {
 	sctx := super.NewContext()