What if every type with differing properties was a discriminant?

src/compiler/checker.ts

@@ -23074,7 +23074,7 @@ namespace ts {
                 if (prop && getCheckFlags(prop) & CheckFlags.SyntheticProperty) {
                     if ((prop as TransientSymbol).isDiscriminantProperty === undefined) {
                         (prop as TransientSymbol).isDiscriminantProperty =
-                            ((prop as TransientSymbol).checkFlags & CheckFlags.Discriminant) === CheckFlags.Discriminant &&
+                            !!((prop as TransientSymbol).checkFlags & CheckFlags.Discriminant) &&
                             !isGenericType(getTypeOfSymbol(prop));
                     }
                     return !!(prop as TransientSymbol).isDiscriminantProperty;

tests/baselines/reference/contextualTypeShouldBeLiteral.symbols

@@ -103,9 +103,12 @@ foo2({
 >method : Symbol(method, Decl(contextualTypeShouldBeLiteral.ts, 40, 18))
 
         this;
+>this : Symbol(Y2, Decl(contextualTypeShouldBeLiteral.ts, 28, 1))
+
         this.value;
->this.value : Symbol(value, Decl(contextualTypeShouldBeLiteral.ts, 25, 15), Decl(contextualTypeShouldBeLiteral.ts, 31, 15))
->value : Symbol(value, Decl(contextualTypeShouldBeLiteral.ts, 25, 15), Decl(contextualTypeShouldBeLiteral.ts, 31, 15))
+>this.value : Symbol(Y2.value, Decl(contextualTypeShouldBeLiteral.ts, 31, 15))
+>this : Symbol(Y2, Decl(contextualTypeShouldBeLiteral.ts, 28, 1))
+>value : Symbol(Y2.value, Decl(contextualTypeShouldBeLiteral.ts, 31, 15))
     }
 });
 

tests/baselines/reference/contextualTypeShouldBeLiteral.types

@@ -99,12 +99,12 @@ foo2({
 >method : () => void
 
         this;
->this : X2 | Y2
+>this : Y2
 
         this.value;
->this.value : string
->this : X2 | Y2
->value : string
+>this.value : "none" | "done"
+>this : Y2
+>value : "none" | "done"
     }
 });
 

tests/baselines/reference/contextualTypeWithUnionTypeObjectLiteral.errors.txt

@@ -1,35 +1,20 @@
-tests/cases/conformance/types/union/contextualTypeWithUnionTypeObjectLiteral.ts(14,5): error TS2322: Type '{ prop: string | number; }' is not assignable to type '{ prop: string; } | { prop: number; }'.
-  Type '{ prop: string | number; }' is not assignable to type '{ prop: number; }'.
-    Types of property 'prop' are incompatible.
-      Type 'string | number' is not assignable to type 'number'.
-        Type 'string' is not assignable to type 'number'.
 tests/cases/conformance/types/union/contextualTypeWithUnionTypeObjectLiteral.ts(20,5): error TS2322: Type '{ prop: string | number; }' is not assignable to type '{ prop: string; anotherP: string; } | { prop: number; }'.
   Type '{ prop: string | number; }' is not assignable to type '{ prop: number; }'.
     Types of property 'prop' are incompatible.
       Type 'string | number' is not assignable to type 'number'.
         Type 'string' is not assignable to type 'number'.
-tests/cases/conformance/types/union/contextualTypeWithUnionTypeObjectLiteral.ts(21,5): error TS2322: Type '{ prop: string | number; anotherP: string; }' is not assignable to type '{ prop: string; anotherP: string; } | { prop: number; }'.
-  Type '{ prop: string | number; anotherP: string; }' is not assignable to type '{ prop: string; anotherP: string; }'.
-    Types of property 'prop' are incompatible.
-      Type 'string | number' is not assignable to type 'string'.
-        Type 'number' is not assignable to type 'string'.
 tests/cases/conformance/types/union/contextualTypeWithUnionTypeObjectLiteral.ts(25,5): error TS2322: Type '{ prop: string | number; anotherP: string; }' is not assignable to type '{ prop: string; anotherP: string; } | { prop: number; anotherP1: number; }'.
   Type '{ prop: string | number; anotherP: string; }' is not assignable to type '{ prop: string; anotherP: string; }'.
     Types of property 'prop' are incompatible.
       Type 'string | number' is not assignable to type 'string'.
         Type 'number' is not assignable to type 'string'.
-tests/cases/conformance/types/union/contextualTypeWithUnionTypeObjectLiteral.ts(29,5): error TS2322: Type '{ prop: string | number; anotherP: string; anotherP1: number; }' is not assignable to type '{ prop: string; anotherP: string; } | { prop: number; anotherP1: number; }'.
-  Type '{ prop: string | number; anotherP: string; anotherP1: number; }' is not assignable to type '{ prop: number; anotherP1: number; }'.
-    Types of property 'prop' are incompatible.
-      Type 'string | number' is not assignable to type 'number'.
-        Type 'string' is not assignable to type 'number'.
 tests/cases/conformance/types/union/contextualTypeWithUnionTypeObjectLiteral.ts(58,5): error TS2322: Type '(a: string, b: number) => string | number' is not assignable to type '((a: string, b: number) => string) | ((a: string, b: number) => number)'.
   Type '(a: string, b: number) => string | number' is not assignable to type '(a: string, b: number) => string'.
     Type 'string | number' is not assignable to type 'string'.
       Type 'number' is not assignable to type 'string'.
 
 
-==== tests/cases/conformance/types/union/contextualTypeWithUnionTypeObjectLiteral.ts (6 errors) ====
+==== tests/cases/conformance/types/union/contextualTypeWithUnionTypeObjectLiteral.ts (3 errors) ====
     var str: string;
     var num: number;
     var strOrNumber: string | number = str || num;
@@ -44,12 +29,6 @@ tests/cases/conformance/types/union/contextualTypeWithUnionTypeObjectLiteral.ts(
     // In case of objStrOrNum3, the S is not union Type but object Literal so we go to next step. 
     // Since T is union Type we only allow the assignment of either object with property of type string or object with property of type number but do not allow object with property of type string | number
     var objStrOrNum3: { prop: string } | { prop: number } = {
-        ~~~~~~~~~~~~
-!!! error TS2322: Type '{ prop: string | number; }' is not assignable to type '{ prop: string; } | { prop: number; }'.
-!!! error TS2322:   Type '{ prop: string | number; }' is not assignable to type '{ prop: number; }'.
-!!! error TS2322:     Types of property 'prop' are incompatible.
-!!! error TS2322:       Type 'string | number' is not assignable to type 'number'.
-!!! error TS2322:         Type 'string' is not assignable to type 'number'.
         prop: strOrNumber
     };
     var objStrOrNum4: { prop: string | number } = {
@@ -63,12 +42,6 @@ tests/cases/conformance/types/union/contextualTypeWithUnionTypeObjectLiteral.ts(
 !!! error TS2322:       Type 'string | number' is not assignable to type 'number'.
 !!! error TS2322:         Type 'string' is not assignable to type 'number'.
     var objStrOrNum6: { prop: string; anotherP: string; } | { prop: number } = {
-        ~~~~~~~~~~~~
-!!! error TS2322: Type '{ prop: string | number; anotherP: string; }' is not assignable to type '{ prop: string; anotherP: string; } | { prop: number; }'.
-!!! error TS2322:   Type '{ prop: string | number; anotherP: string; }' is not assignable to type '{ prop: string; anotherP: string; }'.
-!!! error TS2322:     Types of property 'prop' are incompatible.
-!!! error TS2322:       Type 'string | number' is not assignable to type 'string'.
-!!! error TS2322:         Type 'number' is not assignable to type 'string'.
         prop: strOrNumber,
         anotherP: str
     };
@@ -83,12 +56,6 @@ tests/cases/conformance/types/union/contextualTypeWithUnionTypeObjectLiteral.ts(
         anotherP: str
     };
     var objStrOrNum8: { prop: string; anotherP: string; } | { prop: number; anotherP1: number } = {
-        ~~~~~~~~~~~~
-!!! error TS2322: Type '{ prop: string | number; anotherP: string; anotherP1: number; }' is not assignable to type '{ prop: string; anotherP: string; } | { prop: number; anotherP1: number; }'.
-!!! error TS2322:   Type '{ prop: string | number; anotherP: string; anotherP1: number; }' is not assignable to type '{ prop: number; anotherP1: number; }'.
-!!! error TS2322:     Types of property 'prop' are incompatible.
-!!! error TS2322:       Type 'string | number' is not assignable to type 'number'.
-!!! error TS2322:         Type 'string' is not assignable to type 'number'.
         prop: strOrNumber,
         anotherP: str,
         anotherP1: num

tests/baselines/reference/discriminatedUnionTypes2.errors.txt

@@ -2,9 +2,10 @@ tests/cases/conformance/types/union/discriminatedUnionTypes2.ts(27,30): error TS
   Object literal may only specify known properties, and 'c' does not exist in type '{ a: null; b: string; }'.
 tests/cases/conformance/types/union/discriminatedUnionTypes2.ts(32,11): error TS2339: Property 'b' does not exist on type '{ a: 0; b: string; } | { a: T; c: number; }'.
   Property 'b' does not exist on type '{ a: T; c: number; }'.
+tests/cases/conformance/types/union/discriminatedUnionTypes2.ts(132,11): error TS2339: Property 'value' does not exist on type 'never'.
 
 
-==== tests/cases/conformance/types/union/discriminatedUnionTypes2.ts (2 errors) ====
+==== tests/cases/conformance/types/union/discriminatedUnionTypes2.ts (3 errors) ====
     function f10(x : { kind: false, a: string } | { kind: true, b: string } | { kind: string, c: string }) {
         if (x.kind === false) {
             x.a;
@@ -143,6 +144,8 @@ tests/cases/conformance/types/union/discriminatedUnionTypes2.ts(32,11): error TS
         }
         else {
             x.value;  // number
+              ~~~~~
+!!! error TS2339: Property 'value' does not exist on type 'never'.
         }
     }
 

tests/baselines/reference/discriminatedUnionTypes2.symbols

@@ -367,9 +367,7 @@ function foo1(x: RuntimeValue & { type: 'number' }) {
     }
     else {
         x.value;  // number
->x.value : Symbol(value, Decl(discriminatedUnionTypes2.ts, 122, 23))
 >x : Symbol(x, Decl(discriminatedUnionTypes2.ts, 126, 14))
->value : Symbol(value, Decl(discriminatedUnionTypes2.ts, 122, 23))
     }
 }
 

tests/baselines/reference/discriminatedUnionTypes2.types

@@ -380,9 +380,9 @@ function foo1(x: RuntimeValue & { type: 'number' }) {
     }
     else {
         x.value;  // number
->x.value : number
->x : { type: "number"; value: number; } & { type: "number"; }
->value : number
+>x.value : any
+>x : never
+>value : any
     }
 }
 

tests/baselines/reference/errorsOnUnionsOfOverlappingObjects01.errors.txt

@@ -5,6 +5,7 @@ tests/cases/compiler/errorsOnUnionsOfOverlappingObjects01.ts(18,3): error TS2345
 tests/cases/compiler/errorsOnUnionsOfOverlappingObjects01.ts(19,12): error TS2322: Type 'string' is not assignable to type 'number'.
 tests/cases/compiler/errorsOnUnionsOfOverlappingObjects01.ts(24,5): error TS2345: Argument of type '{ a: string; b: string; }' is not assignable to parameter of type 'Bar | Other'.
   Object literal may only specify known properties, and 'a' does not exist in type 'Bar | Other'.
+tests/cases/compiler/errorsOnUnionsOfOverlappingObjects01.ts(29,12): error TS2322: Type 'string' is not assignable to type 'number'.
 tests/cases/compiler/errorsOnUnionsOfOverlappingObjects01.ts(42,10): error TS2345: Argument of type '{ dog: string; }' is not assignable to parameter of type 'ExoticAnimal'.
   Property 'cat' is missing in type '{ dog: string; }' but required in type 'CatDog'.
 tests/cases/compiler/errorsOnUnionsOfOverlappingObjects01.ts(43,10): error TS2345: Argument of type '{ man: string; bear: string; }' is not assignable to parameter of type 'ExoticAnimal'.
@@ -15,7 +16,7 @@ tests/cases/compiler/errorsOnUnionsOfOverlappingObjects01.ts(47,10): error TS234
   Type '{ man: string; beer: string; }' is missing the following properties from type 'ManBearPig': bear, pig
 
 
-==== tests/cases/compiler/errorsOnUnionsOfOverlappingObjects01.ts (7 errors) ====
+==== tests/cases/compiler/errorsOnUnionsOfOverlappingObjects01.ts (8 errors) ====
     interface Foo {
         a: string;
         b: number;
@@ -55,6 +56,8 @@ tests/cases/compiler/errorsOnUnionsOfOverlappingObjects01.ts(47,10): error TS234
 
     h(x);
     h({ a: '', b: '' })
+               ~
+!!! error TS2322: Type 'string' is not assignable to type 'number'.
 
     interface CatDog { cat: any, dog: any }
     interface ManBearPig { man: any, bear: any, pig: any }

tests/baselines/reference/excessPropertyCheckWithUnions.errors.txt

@@ -1,7 +1,7 @@
 tests/cases/compiler/excessPropertyCheckWithUnions.ts(10,30): error TS2322: Type '{ tag: "T"; a1: string; }' is not assignable to type 'ADT'.
   Object literal may only specify known properties, and 'a1' does not exist in type '{ tag: "T"; }'.
-tests/cases/compiler/excessPropertyCheckWithUnions.ts(11,21): error TS2322: Type '{ tag: "A"; d20: number; }' is not assignable to type 'ADT'.
-  Object literal may only specify known properties, and 'd20' does not exist in type '{ tag: "A"; a1: string; }'.
+tests/cases/compiler/excessPropertyCheckWithUnions.ts(11,1): error TS2322: Type '{ tag: "A"; d20: 12; }' is not assignable to type 'ADT'.
+  Property 'a1' is missing in type '{ tag: "A"; d20: 12; }' but required in type '{ tag: "A"; a1: string; }'.
 tests/cases/compiler/excessPropertyCheckWithUnions.ts(12,1): error TS2322: Type '{ tag: "D"; }' is not assignable to type 'ADT'.
   Property 'd20' is missing in type '{ tag: "D"; }' but required in type '{ tag: "D"; d20: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20; }'.
 tests/cases/compiler/excessPropertyCheckWithUnions.ts(33,28): error TS2322: Type '{ tag: "A"; x: string; extra: number; }' is not assignable to type 'Ambiguous'.
@@ -20,18 +20,14 @@ tests/cases/compiler/excessPropertyCheckWithUnions.ts(49,35): error TS2322: Type
   Object literal may only specify known properties, and 'second' does not exist in type '{ a: 1; b: 1; first: string; }'.
 tests/cases/compiler/excessPropertyCheckWithUnions.ts(50,35): error TS2322: Type '{ a: 1; b: 1; first: string; third: string; }' is not assignable to type 'Overlapping'.
   Object literal may only specify known properties, and 'third' does not exist in type '{ a: 1; b: 1; first: string; }'.
-tests/cases/compiler/excessPropertyCheckWithUnions.ts(66,9): error TS2322: Type '{ kind: "A"; n: { a: string; b: string; }; }' is not assignable to type 'AB'.
-  Types of property 'n' are incompatible.
-    Type '{ a: string; b: string; }' is not assignable to type 'AN'.
-      Object literal may only specify known properties, and 'b' does not exist in type 'AN'.
 tests/cases/compiler/excessPropertyCheckWithUnions.ts(87,5): error TS2322: Type '{ tag: "button"; type: "submit"; href: string; }' is not assignable to type 'Union'.
   Object literal may only specify known properties, and 'href' does not exist in type 'Button'.
 tests/cases/compiler/excessPropertyCheckWithUnions.ts(108,5): error TS2322: Type 'string' is not assignable to type 'IValue'.
 tests/cases/compiler/excessPropertyCheckWithUnions.ts(113,67): error TS2322: Type 'string' is not assignable to type 'number'.
 tests/cases/compiler/excessPropertyCheckWithUnions.ts(114,63): error TS2322: Type 'string' is not assignable to type 'number'.
 
 
-==== tests/cases/compiler/excessPropertyCheckWithUnions.ts (14 errors) ====
+==== tests/cases/compiler/excessPropertyCheckWithUnions.ts (13 errors) ====
     type ADT = {
         tag: "A",
         a1: string
@@ -46,9 +42,10 @@ tests/cases/compiler/excessPropertyCheckWithUnions.ts(114,63): error TS2322: Typ
 !!! error TS2322: Type '{ tag: "T"; a1: string; }' is not assignable to type 'ADT'.
 !!! error TS2322:   Object literal may only specify known properties, and 'a1' does not exist in type '{ tag: "T"; }'.
     wrong = { tag: "A", d20: 12 }
-                        ~~~~~~~
-!!! error TS2322: Type '{ tag: "A"; d20: number; }' is not assignable to type 'ADT'.
-!!! error TS2322:   Object literal may only specify known properties, and 'd20' does not exist in type '{ tag: "A"; a1: string; }'.
+    ~~~~~
+!!! error TS2322: Type '{ tag: "A"; d20: 12; }' is not assignable to type 'ADT'.
+!!! error TS2322:   Property 'a1' is missing in type '{ tag: "A"; d20: 12; }' but required in type '{ tag: "A"; a1: string; }'.
+!!! related TS2728 tests/cases/compiler/excessPropertyCheckWithUnions.ts:3:5: 'a1' is declared here.
     wrong = { tag: "D" }
     ~~~~~
 !!! error TS2322: Type '{ tag: "D"; }' is not assignable to type 'ADT'.
@@ -130,11 +127,6 @@ tests/cases/compiler/excessPropertyCheckWithUnions.ts(114,63): error TS2322: Typ
         n: {
             a: "a",
             b: "b", // excess -- kind: "A"
-            ~~~~~~
-!!! error TS2322: Type '{ kind: "A"; n: { a: string; b: string; }; }' is not assignable to type 'AB'.
-!!! error TS2322:   Types of property 'n' are incompatible.
-!!! error TS2322:     Type '{ a: string; b: string; }' is not assignable to type 'AN'.
-!!! error TS2322:       Object literal may only specify known properties, and 'b' does not exist in type 'AN'.
         }
     }
     const abac: AB = {

tests/baselines/reference/excessPropertyCheckWithUnions.types

@@ -28,12 +28,12 @@ let wrong: ADT = { tag: "T", a1: "extra" }
 >"extra" : "extra"
 
 wrong = { tag: "A", d20: 12 }
->wrong = { tag: "A", d20: 12 } : { tag: "A"; d20: number; }
+>wrong = { tag: "A", d20: 12 } : { tag: "A"; d20: 12; }
 >wrong : ADT
->{ tag: "A", d20: 12 } : { tag: "A"; d20: number; }
+>{ tag: "A", d20: 12 } : { tag: "A"; d20: 12; }
 >tag : "A"
 >"A" : "A"
->d20 : number
+>d20 : 12
 >12 : 12
 
 wrong = { tag: "D" }

tests/baselines/reference/mappedTypeIndexedAccess.errors.txt

@@ -1,9 +1,11 @@
 tests/cases/compiler/mappedTypeIndexedAccess.ts(18,5): error TS2322: Type '{ key: "foo"; value: number; }' is not assignable to type 'Pair<FooBar>'.
-  Types of property 'value' are incompatible.
-    Type 'number' is not assignable to type 'string'.
+  Type '{ key: "foo"; value: number; }' is not assignable to type '{ key: "bar"; value: number; }'.
+    Types of property 'key' are incompatible.
+      Type '"foo"' is not assignable to type '"bar"'.
 tests/cases/compiler/mappedTypeIndexedAccess.ts(24,5): error TS2322: Type '{ key: "foo"; value: number; }' is not assignable to type '{ key: "foo"; value: string; } | { key: "bar"; value: number; }'.
-  Types of property 'value' are incompatible.
-    Type 'number' is not assignable to type 'string'.
+  Type '{ key: "foo"; value: number; }' is not assignable to type '{ key: "bar"; value: number; }'.
+    Types of property 'key' are incompatible.
+      Type '"foo"' is not assignable to type '"bar"'.
 
 
 ==== tests/cases/compiler/mappedTypeIndexedAccess.ts (2 errors) ====
@@ -27,8 +29,9 @@ tests/cases/compiler/mappedTypeIndexedAccess.ts(24,5): error TS2322: Type '{ key
     let pair1: Pair<FooBar> = {
         ~~~~~
 !!! error TS2322: Type '{ key: "foo"; value: number; }' is not assignable to type 'Pair<FooBar>'.
-!!! error TS2322:   Types of property 'value' are incompatible.
-!!! error TS2322:     Type 'number' is not assignable to type 'string'.
+!!! error TS2322:   Type '{ key: "foo"; value: number; }' is not assignable to type '{ key: "bar"; value: number; }'.
+!!! error TS2322:     Types of property 'key' are incompatible.
+!!! error TS2322:       Type '"foo"' is not assignable to type '"bar"'.
         key: "foo",
         value: 3
     };
@@ -37,8 +40,9 @@ tests/cases/compiler/mappedTypeIndexedAccess.ts(24,5): error TS2322: Type '{ key
     let pair2: Pairs<FooBar>[keyof FooBar] = {
         ~~~~~
 !!! error TS2322: Type '{ key: "foo"; value: number; }' is not assignable to type '{ key: "foo"; value: string; } | { key: "bar"; value: number; }'.
-!!! error TS2322:   Types of property 'value' are incompatible.
-!!! error TS2322:     Type 'number' is not assignable to type 'string'.
+!!! error TS2322:   Type '{ key: "foo"; value: number; }' is not assignable to type '{ key: "bar"; value: number; }'.
+!!! error TS2322:     Types of property 'key' are incompatible.
+!!! error TS2322:       Type '"foo"' is not assignable to type '"bar"'.
         key: "foo",
         value: 3
     };

tests/baselines/reference/narrowingDestructuring.types

@@ -145,6 +145,6 @@ function farr<T extends [number, string, string] | [string, number, number]>(x:
         const [head, ...tail] = x;
 >head : "number"
 >tail : (string | number)[]
->x : [number, string, string] | [string, number, number]
+>x : [string, number, number]
     }
 }