fix: canonicalizes record and variant labels during subtype checking

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ## [Unreleased]
 
+- fix: canonicalizes record and variant labels during subtype checking
+
 ## [3.0.1] - 2025-07-22
 
 - fix: override `instanceof` in Candid IDL types to avoid issues when importing `IDL` from multiple locations.

packages/candid/src/idl.test.ts

@@ -1112,6 +1112,12 @@ describe('IDL subtyping', () => {
     testSub(IDL.Tuple(IDL.Tuple(Odd)), Odd);
   });
 
+  describe('Subtyping on records/variants normalizes field labels', () => {
+    // Checks we don't regress https://github.com/dfinity/agent-js/issues/1072
+    testSub(IDL.Record({ a: IDL.Nat, "_98_": IDL.Nat }), IDL.Record({ "_97_": IDL.Nat, b: IDL.Nat }));
+    testSub(IDL.Variant({ a: IDL.Nat, "_98_": IDL.Nat }), IDL.Variant({ "_97_": IDL.Nat, b: IDL.Nat }));
+  });
+
   describe('decoding function/service references', () => {
     const principal = Principal.fromText('w7x7r-cok77-xa');
     it('checks subtyping when decoding function references', () => {

packages/candid/src/idl.ts

@@ -1323,10 +1323,10 @@ export class RecordClass extends ConstructType<Record<string, any>> {
     return x;
   }
 
-  get fieldsAsObject(): Record<string, Type> {
-    const fields: Record<string, Type> = {};
+  get fieldsAsObject(): Record<number, Type> {
+    const fields: Record<number, Type> = {};
     for (const [name, ty] of this._fields) {
-      fields[name] = ty;
+      fields[idlLabelToId(name)] = ty;
     }
     return fields;
   }
@@ -1543,10 +1543,10 @@ export class VariantClass extends ConstructType<Record<string, any>> {
     throw new Error('Variant has no data: ' + x);
   }
 
-  get alternativesAsObject(): Record<string, Type> {
-    const alternatives: Record<string, Type> = {};
+  get alternativesAsObject(): Record<number, Type> {
+    const alternatives: Record<number, Type> = {};
     for (const [name, ty] of this._fields) {
-      alternatives[name] = ty;
+      alternatives[idlLabelToId(name)] = ty;
     }
     return alternatives;
   }
@@ -2438,8 +2438,8 @@ function subtype_(relations: Relations, t1: Type, t2: Type): boolean {
   if (t2 instanceof OptClass) return true;
   if (t1 instanceof RecordClass && t2 instanceof RecordClass) {
     const t1Object = t1.fieldsAsObject;
-    for (const [name, ty2] of t2._fields) {
-      const ty1 = t1Object[name];
+    for (const [label, ty2] of t2._fields) {
+      const ty1 = t1Object[idlLabelToId(label)];
       if (!ty1) {
         if (!canBeOmmitted(ty2)) return false;
       } else {
@@ -2472,8 +2472,8 @@ function subtype_(relations: Relations, t1: Type, t2: Type): boolean {
 
   if (t1 instanceof VariantClass && t2 instanceof VariantClass) {
     const t2Object = t2.alternativesAsObject;
-    for (const [name, ty1] of t1._fields) {
-      const ty2 = t2Object[name];
+    for (const [label, ty1] of t1._fields) {
+      const ty2 = t2Object[idlLabelToId(label)];
       if (!ty2) return false;
       if (!subtype_(relations, ty1, ty2)) return false;
     }