structdiff: fix IsEqual panic on named string map keys

libs/structs/structdiff/diff_test.go

@@ -974,6 +974,14 @@ func TestGetStructDiffNamedStringMapKey(t *testing.T) {
 	assert.Equal(t, []ResolvedChange{{Field: "m['pre']", Old: "a", New: "b"}}, resolveChanges(got))
 }
 
+func TestIsEqualNamedStringMapKey(t *testing.T) {
+	a := namedKeyMapHolder{M: map[namedMapKey]string{"pre": "a", "post": "x"}}
+	b := namedKeyMapHolder{M: map[namedMapKey]string{"pre": "b", "post": "x"}}
+
+	assert.True(t, IsEqual(&a, &a))
+	assert.False(t, IsEqual(&a, &b))
+}
+
 // Types for the "whole block" tests below: two levels of nesting under an
 // optional pointer, mirroring a schema like Outer{Field *Mid{A *Inner{b,c}}}.
 type wbInner struct {

libs/structs/structdiff/equal.go

@@ -155,13 +155,12 @@ func equalStruct(s1, s2 reflect.Value) bool {
 func equalMapStringKey(m1, m2 reflect.Value) bool {
 	keySet := map[string]reflect.Value{}
 	for _, k := range m1.MapKeys() {
-		// Key is always string at this point
-		ks := k.Interface().(string)
-		keySet[ks] = k
+		// Key kind is always String at this point; Value.String() also handles a
+		// named string key type, where a .(string) assertion panics.
+		keySet[k.String()] = k
 	}
 	for _, k := range m2.MapKeys() {
-		ks := k.Interface().(string)
-		keySet[ks] = k
+		keySet[k.String()] = k
 	}
 
 	for _, k := range keySet {