minify: more constant folding for strict equality

Author: evanw

internal/js_ast/js_ast_helpers.go

@@ -1496,6 +1496,12 @@ func CheckEqualityIfNoSideEffects(left E, right E, kind EqualityKind) (equal boo
 		case *ENull, *EUndefined:
 			// "(not null or undefined) == undefined" is false
 			return false, true
+
+		default:
+			if kind == StrictEquality && IsPrimitiveLiteral(right) {
+				// "boolean === (not boolean)" is false
+				return false, true
+			}
 		}
 
 	case *ENumber:
@@ -1523,6 +1529,12 @@ func CheckEqualityIfNoSideEffects(left E, right E, kind EqualityKind) (equal boo
 		case *ENull, *EUndefined:
 			// "(not null or undefined) == undefined" is false
 			return false, true
+
+		default:
+			if kind == StrictEquality && IsPrimitiveLiteral(right) {
+				// "number === (not number)" is false
+				return false, true
+			}
 		}
 
 	case *EBigInt:
@@ -1535,6 +1547,12 @@ func CheckEqualityIfNoSideEffects(left E, right E, kind EqualityKind) (equal boo
 		case *ENull, *EUndefined:
 			// "(not null or undefined) == undefined" is false
 			return false, true
+
+		default:
+			if kind == StrictEquality && IsPrimitiveLiteral(right) {
+				// "bigint === (not bigint)" is false
+				return false, true
+			}
 		}
 
 	case *EString:
@@ -1547,6 +1565,12 @@ func CheckEqualityIfNoSideEffects(left E, right E, kind EqualityKind) (equal boo
 		case *ENull, *EUndefined:
 			// "(not null or undefined) == undefined" is false
 			return false, true
+
+		default:
+			if kind == StrictEquality && IsPrimitiveLiteral(right) {
+				// "string === (not string)" is false
+				return false, true
+			}
 		}
 	}
 

internal/js_parser/js_parser_test.go

@@ -2860,14 +2860,14 @@ func TestConstantFolding(t *testing.T) {
 
 	expectPrinted(t, "x = 1 === 1", "x = true;\n")
 	expectPrinted(t, "x = 1 === 2", "x = false;\n")
-	expectPrinted(t, "x = 1 === '1'", "x = 1 === \"1\";\n")
+	expectPrinted(t, "x = 1 === '1'", "x = false;\n")
 	expectPrinted(t, "x = 1 == 1", "x = true;\n")
 	expectPrinted(t, "x = 1 == 2", "x = false;\n")
 	expectPrinted(t, "x = 1 == '1'", "x = 1 == \"1\";\n")
 
 	expectPrinted(t, "x = 1 !== 1", "x = false;\n")
 	expectPrinted(t, "x = 1 !== 2", "x = true;\n")
-	expectPrinted(t, "x = 1 !== '1'", "x = 1 !== \"1\";\n")
+	expectPrinted(t, "x = 1 !== '1'", "x = true;\n")
 	expectPrinted(t, "x = 1 != 1", "x = false;\n")
 	expectPrinted(t, "x = 1 != 2", "x = true;\n")
 	expectPrinted(t, "x = 1 != '1'", "x = 1 != \"1\";\n")
@@ -2932,6 +2932,8 @@ func TestConstantFolding(t *testing.T) {
 	expectPrinted(t, "x = 0n !== 1n", "x = true;\n")
 	expectPrinted(t, "x = 0n !== 0n", "x = false;\n")
 	expectPrinted(t, "x = 123n === 1_2_3n", "x = true;\n")
+	expectPrinted(t, "x = 0n === '1n'", "x = false;\n")
+	expectPrinted(t, "x = 0n !== '1n'", "x = true;\n")
 
 	expectPrinted(t, "x = 0n === 0b0n", "x = 0n === 0b0n;\n")
 	expectPrinted(t, "x = 0n === 0o0n", "x = 0n === 0o0n;\n")