fix: strictly check operator overload ambiguity (AssemblyScript#2762)

Operator overload is an internal mechanism, it can support to compare user-defined class, but it need to be limited.
a == b and b == a should run the same function and get the same result in semantic level. Allowing ambiguity is bug prone.

src/diagnosticMessages.json

@@ -51,6 +51,7 @@
   "Index signature accessors in type '{0}' differ in types.": 237,
   "Initializer, definitive assignment or nullable type expected.": 238,
   "Definitive assignment has no effect on local variables.": 239,
+  "Ambiguous operator overload '{0}' (conflicting overloads '{1}' and '{2}').": 240,
 
   "Importing the table disables some indirect call optimizations.": 901,
   "Exporting the table disables some indirect call optimizations.": 902,

src/program.ts

@@ -390,8 +390,10 @@ export namespace OperatorKind {
       case Token.GreaterThan_GreaterThan_Equals: return OperatorKind.BitwiseShr;
       case Token.GreaterThan_GreaterThan_GreaterThan:
       case Token.GreaterThan_GreaterThan_GreaterThan_Equals: return OperatorKind.BitwiseShrU;
-      case Token.Equals_Equals: return OperatorKind.Eq;
-      case Token.Exclamation_Equals: return OperatorKind.Ne;
+      case Token.Equals_Equals: 
+      case Token.Equals_Equals_Equals: return OperatorKind.Eq;
+      case Token.Exclamation_Equals: 
+      case Token.Exclamation_Equals_Equals: return OperatorKind.Ne;
       case Token.GreaterThan: return OperatorKind.Gt;
       case Token.GreaterThan_Equals: return OperatorKind.Ge;
       case Token.LessThan: return OperatorKind.Lt;

src/types.ts

@@ -10,7 +10,9 @@ import {
 import {
   Class,
   Program,
-  DecoratorFlags
+  DecoratorFlags,
+  OperatorKind,
+  Function
 } from "./program";
 
 import {
@@ -320,6 +322,14 @@ export class Type {
     return null;
   }
 
+  lookupOverload(kind: OperatorKind, program: Program): Function | null {
+    let classReference = this.getClassOrWrapper(program);
+    if (classReference) {
+      return classReference.lookupOverload(kind);
+    }
+    return null;
+  }
+
   /** Gets the underlying function signature of this type, if any. */
   getSignature(): Signature | null {
     return this.isInternalReference

tests/compiler/operator-overload-ambiguity.json

@@ -0,0 +1,14 @@
+{
+  "asc_flags": [],
+  "stderr": [
+    "AS240: Ambiguous operator overload '==' (conflicting overloads 'operator-overload-ambiguity/A#__eq' and 'operator-overload-ambiguity/B#__eq').",
+    "compare_nonnull_a == compare_nonnull_b;",
+    "AS240: Ambiguous operator overload '==' (conflicting overloads 'operator-overload-ambiguity/B#__eq' and 'operator-overload-ambiguity/A#__eq').",
+    "compare_nonnull_b == compare_nonnull_a;",
+    "AS240: Ambiguous operator overload '==' (conflicting overloads 'operator-overload-ambiguity/C.__eq' and 'operator-overload-ambiguity/D#__eq').",
+    "compare_nonnull_c == compare_nonnull_d;",
+    "AS240: Ambiguous operator overload '==' (conflicting overloads 'operator-overload-ambiguity/A#__eq' and 'operator-overload-ambiguity/B#__eq').",
+    "compare_extend_1 == compare_extend_2;",
+    "EOF"
+  ]
+}

tests/compiler/operator-overload-ambiguity.ts

@@ -0,0 +1,38 @@
+class A {
+  @operator("==") __eq(other: B): bool {
+    return true;
+  }
+}
+class B {
+  @operator("==") __eq(other: A): bool {
+    return true;
+  }
+}
+export function compare_nonnull(compare_nonnull_a: A, compare_nonnull_b: B): void {
+  compare_nonnull_a == compare_nonnull_b;
+  compare_nonnull_b == compare_nonnull_a;
+}
+
+class C {
+  @operator("==") static __eq(self: C | null, other: D | null): bool {
+    return true;
+  }
+}
+class D {
+  @operator("==") __eq(other: i32): bool {
+    return true;
+  }
+}
+export function compare_null(compare_nonnull_c: C | null, compare_nonnull_d: D | null): void {
+  compare_nonnull_c == compare_nonnull_d;
+}
+
+class PA extends A {}
+class PB extends B {}
+export function compare_extend(compare_extend_1: PA, compare_extend_2: PB): void {
+  compare_extend_1 == compare_extend_2;
+}
+
+export function end(): void {
+  ERROR("EOF");
+}