fix(decode): allocate embedded pointer maps and settle case collisions

Assisted-by: GLM 5.3

decode.go

@@ -7,6 +7,7 @@ import (
 	"context"
 	"encoding"
 	"fmt"
+	"maps"
 	"reflect"
 	"slices"
 	"strings"
@@ -337,7 +338,8 @@ func (d *decoder) assignStruct(tbl map[string]any, dst reflect.Value) error {
 	if len(schema.required) > 0 {
 		seen = make(map[string]bool, len(tbl))
 	}
-	for key, val := range tbl {
+	for _, key := range d.tableKeys(tbl) {
+		val := tbl[key]
 		// A key that is already lowercase, which document keys usually are,
 		// hits the map directly; only a miss pays for the case fold.
 		resolved := key
@@ -349,12 +351,15 @@ func (d *decoder) assignStruct(tbl map[string]any, dst reflect.Value) error {
 		if !ok {
 			if schema.embedMaps != nil {
 				// Leftover keys land in an untagged embedded map, the inverse
-				// of the encoder inlining that map's entries.
+				// of the encoder inlining that map's entries. The assign call
+				// rather than assignMap itself lets it allocate the embedded
+				// pointer the field may be, the way any other destination is
+				// reached.
 				mv, err := fieldByIndex(dst, schema.embedMaps[0])
 				if err != nil {
 					return newDecodeError(key, err)
 				}
-				if err := d.assignMap(map[string]any{key: val}, mv); err != nil {
+				if err := d.assign(map[string]any{key: val}, mv); err != nil {
 					return newDecodeError(key, err)
 				}
 			}
@@ -379,6 +384,18 @@ func (d *decoder) assignStruct(tbl map[string]any, dst reflect.Value) error {
 	return nil
 }
 
+// tableKeys returns the keys of tbl in the order the document wrote them
+// when the node index knows it, and in sorted order otherwise, the order a
+// hand-built tree or a node-free parse offers. The order settles which of
+// two keys that differ only in case wins one field: the same key wins every
+// run, instead of whichever a map iteration happened to hand out.
+func (d *decoder) tableKeys(tbl map[string]any) []string {
+	if node := d.nodeOf(tbl); node != nil {
+		return node.Keys()
+	}
+	return slices.Sorted(maps.Keys(tbl))
+}
+
 func (d *decoder) assignMap(tbl map[string]any, dst reflect.Value) error {
 	if dst.Type().Key().Kind() != reflect.String {
 		return fmt.Errorf("interpres: map key must be a string, got %s", dst.Type().Key())
@@ -499,7 +516,7 @@ func (d *decoder) setLocalTimeValue(t time.Time, dst reflect.Value) error {
 				t.Hour(), t.Minute(), t.Second(), t.Nanosecond(), d.loc)))
 			return nil
 		}
-		return fmt.Errorf("interpres: cannot assign local date-time to time.Time; set Decoder.LocalTimeLocation to choose the zone")
+		return fmt.Errorf("interpres: cannot assign local date-time to time.Time; set LocalTimeLocation to choose the zone")
 	}
 	return fmt.Errorf("interpres: cannot assign local date-time to %s", dst.Type())
 }