Discriminant overlap in inference: distribute source, use comparability, optional fast path

tsc/internal/checker/checker.go

@@ -31281,7 +31281,7 @@ func (d *ObjectLiteralDiscriminator) name(index int) string {
 	return d.members[index-len(d.props)].Name()
 }
 
-func (d *ObjectLiteralDiscriminator) matches(index int, t *Type) bool {
+func (d *ObjectLiteralDiscriminator) matches(index int, t *Type, _ bool) bool {
 	var propType *Type
 	if index < len(d.props) {
 		prop := d.props[index]

tsc/internal/checker/inference.go

@@ -250,7 +250,7 @@ func (c *Checker) inferFromTypes(n *InferenceState, source *Type, target *Type)
 		c.inferToUnionOrIntersectionType(n, source, target)
 	case source.flags&TypeFlagsUnion != 0:
 		if discriminants := c.getInferenceDiscriminants(source, target); len(discriminants) != 0 {
-			discriminator := &TypeDiscriminator{c: c, props: discriminants, reverse: true, isRelatedTo: c.compareTypesAssignableSimple}
+			discriminator := &TypeDiscriminator{c: c, props: discriminants, reverse: true, isRelatedTo: c.compareTypesComparableSimple}
 			source = c.discriminateTypeByDiscriminableItems(source, discriminator)
 		}
 		for _, sourceType := range source.Distributed() {
@@ -468,7 +468,7 @@ func (c *Checker) inferToUnionOrIntersectionType(n *InferenceState, source *Type
 		filteredTargetsBySource = make([][]*Type, len(sources))
 		for i, s := range sources {
 			if discriminants := c.getInferenceDiscriminants(target, s); len(discriminants) != 0 {
-				discriminator := &TypeDiscriminator{c: c, props: discriminants, isRelatedTo: c.compareTypesAssignableSimple}
+				discriminator := &TypeDiscriminator{c: c, props: discriminants, isRelatedTo: c.compareTypesComparableSimple}
 				if filtered := c.discriminateTypeByDiscriminableItems(target, discriminator); filtered != target {
 					filteredTargetsBySource[i] = filtered.Distributed()
 				}

tsc/internal/checker/relater.go

@@ -132,6 +132,13 @@ func (c *Checker) compareTypesAssignableSimple(source *Type, target *Type) Terna
 	return TernaryFalse
 }
 
+func (c *Checker) compareTypesComparableSimple(source *Type, target *Type) Ternary {
+	if c.isTypeRelatedTo(source, target, c.comparableRelation) {
+		return TernaryTrue
+	}
+	return TernaryFalse
+}
+
 func (c *Checker) compareTypesAssignableWorker(source *Type, target *Type, reportErrors bool) Ternary {
 	if c.isTypeRelatedTo(source, target, c.assignableRelation) {
 		return TernaryTrue
@@ -1042,7 +1049,12 @@ func (d *TypeDiscriminator) name(index int) string {
 	return d.props[index].Name()
 }
 
-func (d *TypeDiscriminator) matches(index int, t *Type) bool {
+func (d *TypeDiscriminator) matches(index int, t *Type, isOptional bool) bool {
+	// Two optional discriminants always overlap through absence. Under strictNullChecks this is what the
+	// relation below would conclude anyway, so skip the property type resolution and the comparisons.
+	if isOptional && d.c.strictNullChecks && d.props[index].Flags()&ast.SymbolFlagsOptional != 0 {
+		return true
+	}
 	sourceType, targetType := d.c.getTypeOfSymbol(d.props[index]), t
 	if d.reverse {
 		sourceType, targetType = targetType, sourceType
@@ -1201,9 +1213,9 @@ func (c *Checker) mapTypesByKeyProperty(types []*Type, keyPropertyName string) m
 }
 
 type Discriminator interface {
-	len() int                        // Number of discriminant properties
-	name(index int) string           // Property name of index-th discriminator
-	matches(index int, t *Type) bool // True if index-th discriminator matches the given type
+	len() int                                         // Number of discriminant properties
+	name(index int) string                            // Property name of index-th discriminator
+	matches(index int, t *Type, isOptional bool) bool // True if index-th discriminator matches the given type, which is optional if isOptional is set
 }
 
 func (c *Checker) discriminateTypeByDiscriminableItems(target *Type, discriminator Discriminator) *Type {
@@ -1221,9 +1233,17 @@ func (c *Checker) discriminateTypeByDiscriminableItems(target *Type, discriminat
 		matched := false
 		for i := range types {
 			if include[i] != TernaryFalse {
-				targetType := c.getTypeOfPropertyOrIndexSignatureOfType(types[i], discriminator.name(n))
+				name := discriminator.name(n)
+				var targetType *Type
+				isOptional := false
+				if prop := c.getPropertyOfType(types[i], name); prop != nil {
+					targetType = c.getTypeOfSymbol(prop)
+					isOptional = prop.Flags()&ast.SymbolFlagsOptional != 0
+				} else if indexInfo := c.getApplicableIndexInfoForName(types[i], name); indexInfo != nil {
+					targetType = c.addOptionalityEx(indexInfo.valueType, true /*isProperty*/, true /*isOptional*/)
+				}
 				if targetType != nil {
-					if discriminator.matches(n, targetType) {
+					if discriminator.matches(n, targetType, isOptional) {
 						matched = true
 					} else {
 						include[i] = TernaryMaybe

tsc/testdata/baselines/reference/compiler/inferenceDiscriminantOverlap(exactoptionalpropertytypes=false).errors.txt

@@ -35,13 +35,9 @@ inferenceDiscriminantOverlap.ts(39,5): error TS2322: Type '{ tag?: "a" | undefin
     Types of property 'tag' are incompatible.
       Type '"a" | undefined' is not assignable to type '"b" | undefined'.
         Type '"a"' is not assignable to type '"b"'.
-inferenceDiscriminantOverlap.ts(55,5): error TS2322: Type '{ kind: "a"; value: readonly []; }' is not assignable to type '{ kind: string; value: string[]; } | { kind: "a"; value: number; }'.
-  Type '{ kind: "a"; value: readonly []; }' is not assignable to type '{ kind: "a"; value: number; }'.
-    Types of property 'value' are incompatible.
-      Type 'readonly []' is not assignable to type 'number'.
 
 
-==== inferenceDiscriminantOverlap.ts (9 errors) ====
+==== inferenceDiscriminantOverlap.ts (8 errors) ====
     declare const validOptionalSource: { tag: "a"; value: 1 } | { tag?: "a"; value: 2 };
     declare const mixedOptionalSource: { tag: "a"; value: 1 } | { tag?: "b"; value: 2 };
     declare const matchingOptionalSource: { tag: "a"; value: 1 } | { tag?: "a"; value: 2 } | { tag: "b"; value: 3 };
@@ -142,11 +138,6 @@ inferenceDiscriminantOverlap.ts(55,5): error TS2322: Type '{ kind: "a"; value: r
 
     export function broadContext(): { kind: string; value: string[] } | { kind: "a"; value: number } {
         return makeTagged([]);
-        ~~~~~~
-!!! error TS2322: Type '{ kind: "a"; value: readonly []; }' is not assignable to type '{ kind: string; value: string[]; } | { kind: "a"; value: number; }'.
-!!! error TS2322:   Type '{ kind: "a"; value: readonly []; }' is not assignable to type '{ kind: "a"; value: number; }'.
-!!! error TS2322:     Types of property 'value' are incompatible.
-!!! error TS2322:       Type 'readonly []' is not assignable to type 'number'.
     }
     export function partialTagContext(): { kind: "a" | "b"; value: string[] } | { kind: "a"; value: number } {
         return makeTagged([]);

tsc/testdata/baselines/reference/compiler/inferenceDiscriminantOverlap(exactoptionalpropertytypes=false).types

@@ -257,7 +257,7 @@ export function broadContext(): { kind: string; value: string[] } | { kind: "a";
 >value : number
 
     return makeTagged([]);
->makeTagged([]) : { kind: "a"; value: readonly []; }
+>makeTagged([]) : { kind: "a"; value: []; }
 >makeTagged : <const T>(value: T) => { kind: "a"; value: T; }
 >[] : []
 }

tsc/testdata/baselines/reference/compiler/inferenceDiscriminantOverlap(exactoptionalpropertytypes=true).errors.txt

@@ -35,18 +35,14 @@ inferenceDiscriminantOverlap.ts(39,5): error TS2375: Type '{ tag?: "a"; value: 1
   Type '{ tag?: "a"; value: 1 | 2; }' is not assignable to type '{ tag?: "b"; value: 2; }' with 'exactOptionalPropertyTypes: true'. Consider adding 'undefined' to the types of the target's properties.
     Types of property 'tag' are incompatible.
       Type '"a"' is not assignable to type '"b"'.
-inferenceDiscriminantOverlap.ts(55,5): error TS2322: Type '{ kind: "a"; value: readonly []; }' is not assignable to type '{ kind: string; value: string[]; } | { kind: "a"; value: number; }'.
-  Type '{ kind: "a"; value: readonly []; }' is not assignable to type '{ kind: "a"; value: number; }'.
-    Types of property 'value' are incompatible.
-      Type 'readonly []' is not assignable to type 'number'.
 inferenceDiscriminantOverlap.ts(61,5): error TS2375: Type '{ kind: "a" | undefined; value: []; }' is not assignable to type '{ kind?: "a"; value: string[]; } | { kind: "a"; value: number; }' with 'exactOptionalPropertyTypes: true'. Consider adding 'undefined' to the types of the target's properties.
   Type '{ kind: "a" | undefined; value: []; }' is not assignable to type '{ kind: "a"; value: number; }'.
     Types of property 'kind' are incompatible.
       Type '"a" | undefined' is not assignable to type '"a"'.
         Type 'undefined' is not assignable to type '"a"'.
 
 
-==== inferenceDiscriminantOverlap.ts (11 errors) ====
+==== inferenceDiscriminantOverlap.ts (10 errors) ====
     declare const validOptionalSource: { tag: "a"; value: 1 } | { tag?: "a"; value: 2 };
     declare const mixedOptionalSource: { tag: "a"; value: 1 } | { tag?: "b"; value: 2 };
     declare const matchingOptionalSource: { tag: "a"; value: 1 } | { tag?: "a"; value: 2 } | { tag: "b"; value: 3 };
@@ -148,11 +144,6 @@ inferenceDiscriminantOverlap.ts(61,5): error TS2375: Type '{ kind: "a" | undefin
 
     export function broadContext(): { kind: string; value: string[] } | { kind: "a"; value: number } {
         return makeTagged([]);
-        ~~~~~~
-!!! error TS2322: Type '{ kind: "a"; value: readonly []; }' is not assignable to type '{ kind: string; value: string[]; } | { kind: "a"; value: number; }'.
-!!! error TS2322:   Type '{ kind: "a"; value: readonly []; }' is not assignable to type '{ kind: "a"; value: number; }'.
-!!! error TS2322:     Types of property 'value' are incompatible.
-!!! error TS2322:       Type 'readonly []' is not assignable to type 'number'.
     }
     export function partialTagContext(): { kind: "a" | "b"; value: string[] } | { kind: "a"; value: number } {
         return makeTagged([]);

tsc/testdata/baselines/reference/compiler/inferenceDiscriminantOverlap(exactoptionalpropertytypes=true).types

@@ -257,7 +257,7 @@ export function broadContext(): { kind: string; value: string[] } | { kind: "a";
 >value : number
 
     return makeTagged([]);
->makeTagged([]) : { kind: "a"; value: readonly []; }
+>makeTagged([]) : { kind: "a"; value: []; }
 >makeTagged : <const T>(value: T) => { kind: "a"; value: T; }
 >[] : []
 }

tsc/testdata/baselines/reference/compiler/inferenceDiscriminatedUnions1(exactoptionalpropertytypes=false).errors.txt

@@ -2,8 +2,8 @@ inferenceDiscriminatedUnions1.ts(52,17): error TS2345: Argument of type '{ kind:
   Type '{ kind: "b"; value: number; }' is not assignable to type '{ kind: "a"; value: string; }'.
     Types of property 'kind' are incompatible.
       Type '"b"' is not assignable to type '"a"'.
-inferenceDiscriminatedUnions1.ts(53,17): error TS2345: Argument of type '{ kind: string; value: number; } | { kind: "a"; value: string; }' is not assignable to parameter of type '{ kind: "a"; value: string; }'.
-  Type '{ kind: string; value: number; }' is not assignable to type '{ kind: "a"; value: string; }'.
+inferenceDiscriminatedUnions1.ts(53,17): error TS2345: Argument of type '{ kind: string; value: number; } | { kind: "a"; value: string; }' is not assignable to parameter of type '{ kind: "a"; value: number; }'.
+  Type '{ kind: string; value: number; }' is not assignable to type '{ kind: "a"; value: number; }'.
     Types of property 'kind' are incompatible.
       Type 'string' is not assignable to type '"a"'.
 inferenceDiscriminatedUnions1.ts(54,26): error TS2345: Argument of type '{ kind: number; value: number; } | { kind: "a"; value: string; }' is not assignable to parameter of type '{ kind: "a"; value: string; }'.
@@ -121,8 +121,8 @@ inferenceDiscriminatedUnions1.ts(150,68): error TS2345: Argument of type '{ type
 !!! error TS2345:       Type '"b"' is not assignable to type '"a"'.
     const r4 = pick(u2);
                     ~~
-!!! error TS2345: Argument of type '{ kind: string; value: number; } | { kind: "a"; value: string; }' is not assignable to parameter of type '{ kind: "a"; value: string; }'.
-!!! error TS2345:   Type '{ kind: string; value: number; }' is not assignable to type '{ kind: "a"; value: string; }'.
+!!! error TS2345: Argument of type '{ kind: string; value: number; } | { kind: "a"; value: string; }' is not assignable to parameter of type '{ kind: "a"; value: number; }'.
+!!! error TS2345:   Type '{ kind: string; value: number; }' is not assignable to type '{ kind: "a"; value: number; }'.
 !!! error TS2345:     Types of property 'kind' are incompatible.
 !!! error TS2345:       Type 'string' is not assignable to type '"a"'.
     const broadResult = pick(broadTag);

tsc/testdata/baselines/reference/compiler/inferenceDiscriminatedUnions1(exactoptionalpropertytypes=false).types

@@ -252,8 +252,8 @@ const r3 = pick(u1);
 >u1 : { kind: "b"; value: number; } | { kind: "a"; value: string; }
 
 const r4 = pick(u2);
->r4 : string
->pick(u2) : string
+>r4 : number
+>pick(u2) : number
 >pick : <T>(x: { kind: "a"; value: T; }) => T
 >u2 : { kind: string; value: number; } | { kind: "a"; value: string; }
 

tsc/testdata/baselines/reference/compiler/inferenceDiscriminatedUnions1(exactoptionalpropertytypes=true).errors.txt

@@ -2,8 +2,8 @@ inferenceDiscriminatedUnions1.ts(52,17): error TS2345: Argument of type '{ kind:
   Type '{ kind: "b"; value: number; }' is not assignable to type '{ kind: "a"; value: string; }'.
     Types of property 'kind' are incompatible.
       Type '"b"' is not assignable to type '"a"'.
-inferenceDiscriminatedUnions1.ts(53,17): error TS2345: Argument of type '{ kind: string; value: number; } | { kind: "a"; value: string; }' is not assignable to parameter of type '{ kind: "a"; value: string; }'.
-  Type '{ kind: string; value: number; }' is not assignable to type '{ kind: "a"; value: string; }'.
+inferenceDiscriminatedUnions1.ts(53,17): error TS2345: Argument of type '{ kind: string; value: number; } | { kind: "a"; value: string; }' is not assignable to parameter of type '{ kind: "a"; value: number; }'.
+  Type '{ kind: string; value: number; }' is not assignable to type '{ kind: "a"; value: number; }'.
     Types of property 'kind' are incompatible.
       Type 'string' is not assignable to type '"a"'.
 inferenceDiscriminatedUnions1.ts(54,26): error TS2345: Argument of type '{ kind: number; value: number; } | { kind: "a"; value: string; }' is not assignable to parameter of type '{ kind: "a"; value: string; }'.
@@ -121,8 +121,8 @@ inferenceDiscriminatedUnions1.ts(150,68): error TS2345: Argument of type '{ type
 !!! error TS2345:       Type '"b"' is not assignable to type '"a"'.
     const r4 = pick(u2);
                     ~~
-!!! error TS2345: Argument of type '{ kind: string; value: number; } | { kind: "a"; value: string; }' is not assignable to parameter of type '{ kind: "a"; value: string; }'.
-!!! error TS2345:   Type '{ kind: string; value: number; }' is not assignable to type '{ kind: "a"; value: string; }'.
+!!! error TS2345: Argument of type '{ kind: string; value: number; } | { kind: "a"; value: string; }' is not assignable to parameter of type '{ kind: "a"; value: number; }'.
+!!! error TS2345:   Type '{ kind: string; value: number; }' is not assignable to type '{ kind: "a"; value: number; }'.
 !!! error TS2345:     Types of property 'kind' are incompatible.
 !!! error TS2345:       Type 'string' is not assignable to type '"a"'.
     const broadResult = pick(broadTag);

tsc/testdata/baselines/reference/compiler/inferenceDiscriminatedUnions1(exactoptionalpropertytypes=true).types

@@ -252,8 +252,8 @@ const r3 = pick(u1);
 >u1 : { kind: "b"; value: number; } | { kind: "a"; value: string; }
 
 const r4 = pick(u2);
->r4 : string
->pick(u2) : string
+>r4 : number
+>pick(u2) : number
 >pick : <T>(x: { kind: "a"; value: T; }) => T
 >u2 : { kind: string; value: number; } | { kind: "a"; value: string; }