Revise discriminateTypeByDiscriminableItems function

src/compiler/checker.ts

@@ -22607,41 +22607,41 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
     }
 
     function getBestMatchingType(source: Type, target: UnionOrIntersectionType, isRelatedTo = compareTypesAssignable) {
-        return findMatchingDiscriminantType(source, target, isRelatedTo, /*skipPartial*/ true) ||
+        return findMatchingDiscriminantType(source, target, isRelatedTo) ||
             findMatchingTypeReferenceOrTypeAliasReference(source, target) ||
             findBestTypeForObjectLiteral(source, target) ||
             findBestTypeForInvokable(source, target) ||
             findMostOverlappyType(source, target);
     }
 
-    function discriminateTypeByDiscriminableItems(target: UnionType, discriminators: [() => Type, __String][], related: (source: Type, target: Type) => boolean | Ternary, defaultValue?: undefined, skipPartial?: boolean): Type | undefined;
-    function discriminateTypeByDiscriminableItems(target: UnionType, discriminators: [() => Type, __String][], related: (source: Type, target: Type) => boolean | Ternary, defaultValue: Type, skipPartial?: boolean): Type;
-    function discriminateTypeByDiscriminableItems(target: UnionType, discriminators: [() => Type, __String][], related: (source: Type, target: Type) => boolean | Ternary, defaultValue?: Type, skipPartial?: boolean) {
-        // undefined=unknown, true=discriminated, false=not discriminated
-        // The state of each type progresses from left to right. Discriminated types stop at 'true'.
-        const discriminable = target.types.map(_ => undefined) as (boolean | undefined)[];
+    function discriminateTypeByDiscriminableItems(target: UnionType, discriminators: [() => Type, __String][], related: (source: Type, target: Type) => boolean | Ternary) {
+        const types = target.types;
+        const include: Ternary[] = types.map(t => t.flags & TypeFlags.Primitive ? Ternary.False : Ternary.True);
         for (const [getDiscriminatingType, propertyName] of discriminators) {
-            const targetProp = getUnionOrIntersectionProperty(target, propertyName);
-            if (skipPartial && targetProp && getCheckFlags(targetProp) & CheckFlags.ReadPartial) {
-                continue;
-            }
-            let i = 0;
-            for (const type of target.types) {
-                const targetType = getTypeOfPropertyOfType(type, propertyName);
-                if (targetType && related(getDiscriminatingType(), targetType)) {
-                    discriminable[i] = discriminable[i] === undefined ? true : discriminable[i];
+            // If the remaining target types include at least one with a matching discriminant, eliminate those that
+            // have non-matching discriminants. This ensures that we ignore erroneous discriminators and gradually
+            // refine the target set without eliminating every constituent (which would lead to `never`).
+            let matched = false;
+            for (let i = 0; i < types.length; i++) {
+                if (include[i]) {
+                    const targetType = getTypeOfPropertyOfType(types[i], propertyName);
+                    if (targetType && related(getDiscriminatingType(), targetType)) {
+                        matched = true;
+                    }
+                    else {
+                        include[i] = Ternary.Maybe;
+                    }
                 }
-                else {
-                    discriminable[i] = false;
+            }
+            // Turn each Ternary.Maybe into Ternary.False if there was a match. Otherwise, revert to Ternary.True.
+            for (let i = 0; i < types.length; i++) {
+                if (include[i] === Ternary.Maybe) {
+                    include[i] = matched ? Ternary.False : Ternary.True;
                 }
-                i++;
             }
         }
-        const match = discriminable.indexOf(/*searchElement*/ true);
-        if (match === -1) {
-            return defaultValue;
-        }
-        return getUnionType(target.types.filter((_, index) => discriminable[index]));
+        const filtered = contains(include, Ternary.False) ? getUnionType(types.filter((_, i) => include[i])) : target;
+        return filtered.flags & TypeFlags.Never ? target : filtered;
     }
 
     /**
@@ -29276,8 +29276,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                     s => [() => undefinedType, s.escapedName] as [() => Type, __String]
                 )
             ),
-            isTypeAssignableTo,
-            contextualType
+            isTypeAssignableTo
         );
     }
 
@@ -29293,8 +29292,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                     s => [() => undefinedType, s.escapedName] as [() => Type, __String]
                 )
             ),
-            isTypeAssignableTo,
-            contextualType
+            isTypeAssignableTo
         );
     }
 
@@ -48739,7 +48737,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
     }
 
     // Keep this up-to-date with the same logic within `getApparentTypeOfContextualType`, since they should behave similarly
-    function findMatchingDiscriminantType(source: Type, target: Type, isRelatedTo: (source: Type, target: Type) => Ternary, skipPartial?: boolean) {
+    function findMatchingDiscriminantType(source: Type, target: Type, isRelatedTo: (source: Type, target: Type) => Ternary) {
         if (target.flags & TypeFlags.Union && source.flags & (TypeFlags.Intersection | TypeFlags.Object)) {
             const match = getMatchingUnionConstituentForType(target as UnionType, source);
             if (match) {
@@ -48749,7 +48747,10 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
             if (sourceProperties) {
                 const sourcePropertiesFiltered = findDiscriminantProperties(sourceProperties, target);
                 if (sourcePropertiesFiltered) {
-                    return discriminateTypeByDiscriminableItems(target as UnionType, map(sourcePropertiesFiltered, p => ([() => getTypeOfSymbol(p), p.escapedName] as [() => Type, __String])), isRelatedTo, /*defaultValue*/ undefined, skipPartial);
+                    const discriminated = discriminateTypeByDiscriminableItems(target as UnionType, map(sourcePropertiesFiltered, p => ([() => getTypeOfSymbol(p), p.escapedName] as [() => Type, __String])), isRelatedTo);
+                    if (discriminated !== target) {
+                        return discriminated;
+                    }
                 }
             }
         }

tests/baselines/reference/assignmentCompatWithDiscriminatedUnion.errors.txt

@@ -1,15 +1,13 @@
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithDiscriminatedUnion.ts(44,5): error TS2322: Type 'S' is not assignable to type 'T'.
-  Type 'S' is not assignable to type '{ a: 2; b: 3; }'.
-    Types of property 'a' are incompatible.
-      Type '0 | 2' is not assignable to type '2'.
-        Type '0' is not assignable to type '2'.
+  Type 'S' is not assignable to type '{ a: 0; b: 4 | 1; } | { a: 1; b: 2 | 4; }'.
+    Type 'S' is not assignable to type '{ a: 1; b: 2 | 4; }'.
+      Types of property 'a' are incompatible.
+        Type '0 | 2' is not assignable to type '1'.
+          Type '0' is not assignable to type '1'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithDiscriminatedUnion.ts(58,5): error TS2322: Type 'S' is not assignable to type 'T'.
-  Property 'c' is missing in type 'S' but required in type '{ a: 2; b: 4 | 3; c: string; }'.
+  Type 'S' is not assignable to type '{ a: 0; b: 4 | 1; } | { a: 2; b: 4 | 3; c: string; }'.
+    Property 'c' is missing in type 'S' but required in type '{ a: 2; b: 4 | 3; c: string; }'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithDiscriminatedUnion.ts(82,5): error TS2322: Type 'S' is not assignable to type 'T'.
-  Type 'S' is not assignable to type '{ a: N; b: N; c: 2; }'.
-    Types of property 'c' are incompatible.
-      Type 'N' is not assignable to type '2'.
-        Type '0' is not assignable to type '2'.
 
 
 ==== tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithDiscriminatedUnion.ts (3 errors) ====
@@ -59,10 +57,11 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
         t = s;
         ~
 !!! error TS2322: Type 'S' is not assignable to type 'T'.
-!!! error TS2322:   Type 'S' is not assignable to type '{ a: 2; b: 3; }'.
-!!! error TS2322:     Types of property 'a' are incompatible.
-!!! error TS2322:       Type '0 | 2' is not assignable to type '2'.
-!!! error TS2322:         Type '0' is not assignable to type '2'.
+!!! error TS2322:   Type 'S' is not assignable to type '{ a: 0; b: 4 | 1; } | { a: 1; b: 2 | 4; }'.
+!!! error TS2322:     Type 'S' is not assignable to type '{ a: 1; b: 2 | 4; }'.
+!!! error TS2322:       Types of property 'a' are incompatible.
+!!! error TS2322:         Type '0 | 2' is not assignable to type '1'.
+!!! error TS2322:           Type '0' is not assignable to type '1'.
     }
 
     // Unmatched non-discriminants
@@ -79,7 +78,8 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
         t = s;
         ~
 !!! error TS2322: Type 'S' is not assignable to type 'T'.
-!!! error TS2322:   Property 'c' is missing in type 'S' but required in type '{ a: 2; b: 4 | 3; c: string; }'.
+!!! error TS2322:   Type 'S' is not assignable to type '{ a: 0; b: 4 | 1; } | { a: 2; b: 4 | 3; c: string; }'.
+!!! error TS2322:     Property 'c' is missing in type 'S' but required in type '{ a: 2; b: 4 | 3; c: string; }'.
 !!! related TS2728 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithDiscriminatedUnion.ts:52:36: 'c' is declared here.
     }
 
@@ -107,10 +107,6 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
         t = s;
         ~
 !!! error TS2322: Type 'S' is not assignable to type 'T'.
-!!! error TS2322:   Type 'S' is not assignable to type '{ a: N; b: N; c: 2; }'.
-!!! error TS2322:     Types of property 'c' are incompatible.
-!!! error TS2322:       Type 'N' is not assignable to type '2'.
-!!! error TS2322:         Type '0' is not assignable to type '2'.
     }
 
     // https://github.com/Microsoft/TypeScript/issues/14865

tests/baselines/reference/excessPropertyCheckWithMultipleDiscriminants.errors.txt

@@ -10,8 +10,10 @@ tests/cases/compiler/excessPropertyCheckWithMultipleDiscriminants.ts(83,5): erro
   Object literal may only specify known properties, and 'b' does not exist in type 'Common | (Common & A)'.
 tests/cases/compiler/excessPropertyCheckWithMultipleDiscriminants.ts(93,5): error TS2322: Type '{ type: "A"; n: number; a: number; b: number; }' is not assignable to type 'CommonWithDisjointOverlappingOptionals'.
   Object literal may only specify known properties, and 'b' does not exist in type 'Common | A'.
-tests/cases/compiler/excessPropertyCheckWithMultipleDiscriminants.ts(130,5): error TS2322: Type '"string"' is not assignable to type '"number"'.
-tests/cases/compiler/excessPropertyCheckWithMultipleDiscriminants.ts(136,5): error TS2322: Type '"string"' is not assignable to type '"number"'.
+tests/cases/compiler/excessPropertyCheckWithMultipleDiscriminants.ts(131,5): error TS2322: Type '{ type: "string"; autoIncrement: boolean; required: true; }' is not assignable to type 'Attribute'.
+  Object literal may only specify known properties, and 'autoIncrement' does not exist in type 'StringAttribute | OneToOneAttribute'.
+tests/cases/compiler/excessPropertyCheckWithMultipleDiscriminants.ts(137,5): error TS2322: Type '{ type: "string"; autoIncrement: boolean; required: true; }' is not assignable to type 'Attribute2'.
+  Object literal may only specify known properties, and 'autoIncrement' does not exist in type 'StringAttribute'.
 
 
 ==== tests/cases/compiler/excessPropertyCheckWithMultipleDiscriminants.ts (8 errors) ====
@@ -163,17 +165,19 @@ tests/cases/compiler/excessPropertyCheckWithMultipleDiscriminants.ts(136,5): err
     // both should error due to excess properties
     const attributes: Attribute = {
         type: 'string',
-        ~~~~
-!!! error TS2322: Type '"string"' is not assignable to type '"number"'.
         autoIncrement: true,
+        ~~~~~~~~~~~~~
+!!! error TS2322: Type '{ type: "string"; autoIncrement: boolean; required: true; }' is not assignable to type 'Attribute'.
+!!! error TS2322:   Object literal may only specify known properties, and 'autoIncrement' does not exist in type 'StringAttribute | OneToOneAttribute'.
         required: true,
     };
 
     const attributes2: Attribute2 = {
         type: 'string',
-        ~~~~
-!!! error TS2322: Type '"string"' is not assignable to type '"number"'.
         autoIncrement: true,
+        ~~~~~~~~~~~~~
+!!! error TS2322: Type '{ type: "string"; autoIncrement: boolean; required: true; }' is not assignable to type 'Attribute2'.
+!!! error TS2322:   Object literal may only specify known properties, and 'autoIncrement' does not exist in type 'StringAttribute'.
         required: true,
     };
 

tests/baselines/reference/jsxComponentTypeErrors.errors.txt

@@ -17,7 +17,8 @@ tests/cases/compiler/jsxComponentTypeErrors.tsx(27,16): error TS2786: 'ClassComp
 tests/cases/compiler/jsxComponentTypeErrors.tsx(28,16): error TS2786: 'MixedComponent' cannot be used as a JSX component.
   Its element type 'ClassComponent | { type: string | undefined; }' is not a valid JSX element.
     Type 'ClassComponent' is not assignable to type 'Element | ElementClass | null'.
-      Type 'ClassComponent' is not assignable to type 'ElementClass'.
+      Type 'ClassComponent' is not assignable to type 'Element | ElementClass'.
+        Type 'ClassComponent' is not assignable to type 'ElementClass'.
 tests/cases/compiler/jsxComponentTypeErrors.tsx(37,16): error TS2786: 'obj.MemberFunctionComponent' cannot be used as a JSX component.
   Its return type '{}' is not a valid JSX element.
     Property 'type' is missing in type '{}' but required in type 'Element'.
@@ -79,7 +80,8 @@ tests/cases/compiler/jsxComponentTypeErrors.tsx(38,16): error TS2786: 'obj. Memb
 !!! error TS2786: 'MixedComponent' cannot be used as a JSX component.
 !!! error TS2786:   Its element type 'ClassComponent | { type: string | undefined; }' is not a valid JSX element.
 !!! error TS2786:     Type 'ClassComponent' is not assignable to type 'Element | ElementClass | null'.
-!!! error TS2786:       Type 'ClassComponent' is not assignable to type 'ElementClass'.
+!!! error TS2786:       Type 'ClassComponent' is not assignable to type 'Element | ElementClass'.
+!!! error TS2786:         Type 'ClassComponent' is not assignable to type 'ElementClass'.
 
     const obj = {
       MemberFunctionComponent() {

tests/baselines/reference/objectLiteralNormalization.errors.txt

@@ -5,9 +5,8 @@ tests/cases/conformance/expressions/objectLiterals/objectLiteralNormalization.ts
 tests/cases/conformance/expressions/objectLiterals/objectLiteralNormalization.ts(9,1): error TS2322: Type '{ c: true; }' is not assignable to type '{ a: number; b?: undefined; c?: undefined; } | { a: number; b: string; c?: undefined; } | { a: number; b: string; c: boolean; }'.
   Type '{ c: true; }' is missing the following properties from type '{ a: number; b: string; c: boolean; }': a, b
 tests/cases/conformance/expressions/objectLiterals/objectLiteralNormalization.ts(17,1): error TS2322: Type '{ a: string; b: number; }' is not assignable to type '{ a: number; b: number; } | { a: string; b?: undefined; } | { a?: undefined; b?: undefined; }'.
-  Type '{ a: string; b: number; }' is not assignable to type '{ a?: undefined; b?: undefined; }'.
-    Types of property 'a' are incompatible.
-      Type 'string' is not assignable to type 'undefined'.
+  Types of property 'b' are incompatible.
+    Type 'number' is not assignable to type 'undefined'.
 tests/cases/conformance/expressions/objectLiterals/objectLiteralNormalization.ts(18,1): error TS2322: Type '{ a: number; }' is not assignable to type '{ a: number; b: number; } | { a: string; b?: undefined; } | { a?: undefined; b?: undefined; }'.
   Property 'b' is missing in type '{ a: number; }' but required in type '{ a: number; b: number; }'.
 tests/cases/conformance/expressions/objectLiterals/objectLiteralNormalization.ts(48,20): error TS2322: Type '2' is not assignable to type '1'.
@@ -44,9 +43,8 @@ tests/cases/conformance/expressions/objectLiterals/objectLiteralNormalization.ts
     a2 = { a: "def", b: 20 };  // Error
     ~~
 !!! error TS2322: Type '{ a: string; b: number; }' is not assignable to type '{ a: number; b: number; } | { a: string; b?: undefined; } | { a?: undefined; b?: undefined; }'.
-!!! error TS2322:   Type '{ a: string; b: number; }' is not assignable to type '{ a?: undefined; b?: undefined; }'.
-!!! error TS2322:     Types of property 'a' are incompatible.
-!!! error TS2322:       Type 'string' is not assignable to type 'undefined'.
+!!! error TS2322:   Types of property 'b' are incompatible.
+!!! error TS2322:     Type 'number' is not assignable to type 'undefined'.
     a2 = { a: 1 };  // Error
     ~~
 !!! error TS2322: Type '{ a: number; }' is not assignable to type '{ a: number; b: number; } | { a: string; b?: undefined; } | { a?: undefined; b?: undefined; }'.

tests/cases/fourslash/completionsUnionStringLiteralProperty.ts

@@ -0,0 +1,19 @@
+/// <reference path="fourslash.ts" />
+
+//// type Foo = { a: 0, b: 'x' } | { a: 0, b: 'y' } | { a: 1, b: 'z' };
+//// const foo: Foo = { a: 0, b: '/*1*/' }
+////
+//// type Bar = { a: 0, b: 'fx' } | { a: 0, b: 'fy' } | { a: 1, b: 'fz' };
+//// const bar: Bar = { a: 0, b: 'f/*2*/' }
+////
+//// type Baz = { x: 0, y: 0, z: 'a' } | { x: 0, y: 1, z: 'b' } | { x: 1, y: 0, z: 'c' } | { x: 1, y: 1, z: 'd' };
+//// const baz1: Baz = { z: '/*3*/' };
+//// const baz2: Baz = { x: 0, z: '/*4*/' };
+//// const baz3: Baz = { x: 0, y: 1, z: '/*5*/' };
+//// const baz4: Baz = { x: 2, y: 1, z: '/*6*/' };
+verify.completions({ marker: "1", triggerCharacter: "'", includes: [ "x", "y" ], excludes: [ "z" ] });
+verify.completions({ marker: "2", triggerCharacter: "'", includes: [ "fx", "fy" ], excludes: [ "fz" ] });
+verify.completions({ marker: "3", triggerCharacter: "'", includes: [ "a", "b", "c", "d" ] });
+verify.completions({ marker: "4", triggerCharacter: "'", includes: [ "a", "b" ], excludes: [ "c", "d" ] });
+verify.completions({ marker: "5", triggerCharacter: "'", includes: [ "b" ], excludes: [ "a", "c", "d" ] });
+verify.completions({ marker: "6", triggerCharacter: "'", includes: [ "b", "d" ], excludes: [ "a", "c" ] });