Per-file strictNullChecks support

Author: weswigham

src/compiler/checker.ts

@@ -4386,9 +4386,9 @@ namespace ts {
         /* @internal */ getParameterType(signature: Signature, parameterIndex: number): Type;
         /* @internal */ getParameterIdentifierNameAtPosition(signature: Signature, parameterIndex: number): [parameterName: __String, isRestParameter: boolean] | undefined;
         getNullableType(type: Type, flags: TypeFlags): Type;
-        getNonNullableType(type: Type): Type;
+        getNonNullableType(type: Type, context?: Node | undefined): Type;
         /* @internal */ getNonOptionalType(type: Type): Type;
-        /* @internal */ isNullableType(type: Type): boolean;
+        /* @internal */ isNullableType(type: Type, context?: Node | undefined): boolean;
         getTypeArguments(type: TypeReference): readonly Type[];
 
         // TODO: GH#18217 `xToDeclaration` calls are frequently asserted as defined.
@@ -4520,8 +4520,8 @@ namespace ts {
         /* @internal */ getFalseType(fresh?: boolean): Type;
         /* @internal */ getTrueType(fresh?: boolean): Type;
         /* @internal */ getVoidType(): Type;
-        /* @internal */ getUndefinedType(): Type;
-        /* @internal */ getNullType(): Type;
+        /* @internal */ getUndefinedType(widening?: boolean): Type;
+        /* @internal */ getNullType(widening?: boolean): Type;
         /* @internal */ getESSymbolType(): Type;
         /* @internal */ getNeverType(): Type;
         /* @internal */ getOptionalType(): Type;
@@ -5416,12 +5416,12 @@ namespace ts {
         Narrowable = Any | Unknown | StructuredOrInstantiable | StringLike | NumberLike | BigIntLike | BooleanLike | ESSymbol | UniqueESSymbol | NonPrimitive,
         // The following flags are aggregated during union and intersection type construction
         /* @internal */
-        IncludesMask = Any | Unknown | Primitive | Never | Object | Union | Intersection | NonPrimitive | TemplateLiteral,
+        IncludesMask = Any | Unknown | Primitive | Never | Object | Union | Intersection | NonPrimitive | TemplateLiteral | Index | StringMapping,
         // The following flags are used for different purposes during union and intersection type construction
         /* @internal */
         IncludesMissingType = TypeParameter,
         /* @internal */
-        IncludesNonWideningType = Index,
+        IncludesNonWideningType = 1 << 29, // repurpose for true typeflag when needed
         /* @internal */
         IncludesWildcard = IndexedAccess,
         /* @internal */

src/compiler/types.ts

@@ -2323,7 +2323,7 @@ declare namespace ts {
         getWidenedType(type: Type): Type;
         getReturnTypeOfSignature(signature: Signature): Type;
         getNullableType(type: Type, flags: TypeFlags): Type;
-        getNonNullableType(type: Type): Type;
+        getNonNullableType(type: Type, context?: Node | undefined): Type;
         getTypeArguments(type: TypeReference): readonly Type[];
         /** Note that the resulting nodes cannot be checked. */
         typeToTypeNode(type: Type, enclosingDeclaration: Node | undefined, flags: NodeBuilderFlags | undefined): TypeNode | undefined;

src/services/codefixes/inferFromUsage.ts

@@ -2323,7 +2323,7 @@ declare namespace ts {
         getWidenedType(type: Type): Type;
         getReturnTypeOfSignature(signature: Signature): Type;
         getNullableType(type: Type, flags: TypeFlags): Type;
-        getNonNullableType(type: Type): Type;
+        getNonNullableType(type: Type, context?: Node | undefined): Type;
         getTypeArguments(type: TypeReference): readonly Type[];
         /** Note that the resulting nodes cannot be checked. */
         typeToTypeNode(type: Type, enclosingDeclaration: Node | undefined, flags: NodeBuilderFlags | undefined): TypeNode | undefined;

tests/baselines/reference/api/tsserverlibrary.d.ts

@@ -23,7 +23,7 @@ function fetchMsg<V extends Message>(protoCtor: MsgConstructor<V>): V {
 >protoCtor : MsgConstructor<V>
 
   return null!;
->null! : null
+>null! : never
 >null : null
 }
 

tests/baselines/reference/api/typescript.d.ts

@@ -148,7 +148,6 @@ tests/cases/conformance/types/conditional/conditionalTypes2.ts(75,12): error TS2
 !!! error TS2345:   Property 'bat' is missing in type 'Bar & Foo' but required in type '{ foo: string; bat: string; }'.
 !!! error TS2345:     Type 'Extract<T, Bar>' is not assignable to type '{ foo: string; bat: string; }'.
 !!! error TS2345:       Property 'bat' is missing in type 'Bar & Foo' but required in type '{ foo: string; bat: string; }'.
-!!! related TS2728 tests/cases/conformance/types/conditional/conditionalTypes2.ts:62:43: 'bat' is declared here.
 !!! related TS2728 tests/cases/conformance/types/conditional/conditionalTypes2.ts:62:43: 'bat' is declared here.
         fooBat(y);  // Error
                ~

tests/baselines/reference/circularlyConstrainedMappedTypeContainingConditionalNoInfiniteInstantiationDepth.errors.txt

@@ -15,7 +15,7 @@ function fn<T extends { x: Map<T['x']> }>(sliceIndex: T): AllArg<T['x']> {
 >sliceIndex : T
 
     return null!;
->null! : null
+>null! : never
 >null : null
 }
 

tests/baselines/reference/collectionPatternNoError.types

@@ -80,7 +80,7 @@ class HelloWorld {
   handleEvent3(event: C3): T1 { return undefined! } // Ok, Error
 >handleEvent3 : (event: C3) => T1
 >event : C3
->undefined! : undefined
+>undefined! : never
 >undefined : undefined
 }
 

tests/baselines/reference/conditionalTypes2.errors.txt

@@ -80,7 +80,7 @@ class HelloWorld {
   handleEvent3(event: C3): T1 { return undefined! } // Ok, Error
 >handleEvent3 : (event: C3) => T1
 >event : C3
->undefined! : undefined
+>undefined! : never
 >undefined : undefined
 }
 

tests/baselines/reference/declarationEmitMappedTypeDistributivityPreservesConstraints.types

@@ -9,7 +9,7 @@ tests/cases/compiler/genericConditionalConstrainedToUnknownNotAssignableToConcre
                 Type 'unknown' is not assignable to type 'A'.
                   Type 'ReturnType<FunctionsObj<T>[string]>' is not assignable to type 'A'.
                     Type 'unknown' is not assignable to type 'A'.
-                      Property 'x' is missing in type '{}' but required in type 'A'.
+                      Type 'unknown' is not assignable to type 'A'.
 
 
 ==== tests/cases/compiler/genericConditionalConstrainedToUnknownNotAssignableToConcreteObject.ts (1 errors) ====
@@ -38,8 +38,7 @@ tests/cases/compiler/genericConditionalConstrainedToUnknownNotAssignableToConcre
 !!! error TS2322:                 Type 'unknown' is not assignable to type 'A'.
 !!! error TS2322:                   Type 'ReturnType<FunctionsObj<T>[string]>' is not assignable to type 'A'.
 !!! error TS2322:                     Type 'unknown' is not assignable to type 'A'.
-!!! error TS2322:                       Property 'x' is missing in type '{}' but required in type 'A'.
-!!! related TS2728 tests/cases/compiler/genericConditionalConstrainedToUnknownNotAssignableToConcreteObject.ts:1:15: 'x' is declared here.
+!!! error TS2322:                       Type 'unknown' is not assignable to type 'A'.
     }
 
     // Original CFA report of the above issue

tests/baselines/reference/emitDecoratorMetadata_isolatedModules(module=commonjs).types

@@ -79,7 +79,7 @@ function union2<T extends object, U extends string | number>(thing: T | U) {
     "key" in thing; // Ok
 >"key" in thing : boolean
 >"key" : "key"
->thing : T
+>thing : T | (T & null) | (U & null)
   }
 }
 
@@ -146,7 +146,7 @@ function union5<T extends object | string, U extends object | number>(p: T | U)
         "key" in p;
 >"key" in p : boolean
 >"key" : "key"
->p : (T & object) | (U & object)
+>p : (T & object) | (U & object) | (T & null) | (U & null)
     }
 }
 

tests/baselines/reference/emitDecoratorMetadata_isolatedModules(module=esnext).types

@@ -40,12 +40,12 @@ type N1 = 'a' & 'b';
 >N1 : never
 
 type N2 = { a: string } & null;
->N2 : null
+>N2 : never
 >a : string
 >null : null
 
 type N3 = { a: string } & undefined;
->N3 : undefined
+>N3 : never
 >a : string
 
 type N4 = string & number;
@@ -255,10 +255,10 @@ declare let s2: string & Tag2;
 >s2 : never
 
 declare let t1: string & Tag1 | undefined;
->t1 : undefined
+>t1 : never
 
 declare let t2: string & Tag2 | undefined;
->t2 : undefined
+>t2 : never
 
 s1 = s2;
 >s1 = s2 : never
@@ -271,14 +271,14 @@ s2 = s1;
 >s1 : never
 
 t1 = t2;
->t1 = t2 : undefined
->t1 : undefined
->t2 : undefined
+>t1 = t2 : never
+>t1 : never
+>t2 : never
 
 t2 = t1;
->t2 = t1 : undefined
->t2 : undefined
->t1 : undefined
+>t2 = t1 : never
+>t2 : never
+>t1 : never
 
 // Repro from #36736
 

tests/baselines/reference/genericConditionalConstrainedToUnknownNotAssignableToConcreteObject.errors.txt

@@ -20,7 +20,7 @@ class Table<S extends Schema>  {
 >getRows : <C extends keyof S>() => Array<UnrollOnHover<Pick<S, C>>>
 
         return null!
->null! : null
+>null! : never
 >null : null
     }
 }

tests/baselines/reference/inDoesNotOperateOnPrimitiveTypes.types

@@ -17,12 +17,18 @@ tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(40,5): error TS2
 tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(41,5): error TS2322: Type 'T[keyof T]' is not assignable to type 'U[keyof T] | undefined'.
   Type 'T[string] | T[number] | T[symbol]' is not assignable to type 'U[keyof T] | undefined'.
     Type 'T[string]' is not assignable to type 'U[keyof T] | undefined'.
+      Type 'T[string]' is not assignable to type 'U[keyof T]'.
+        Type 'T' is not assignable to type 'U'.
+          'U' could be instantiated with an arbitrary type which could be unrelated to 'T'.
 tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(45,5): error TS2322: Type 'U[K] | undefined' is not assignable to type 'T[K]'.
   Type 'undefined' is not assignable to type 'T[K]'.
 tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(46,5): error TS2322: Type 'T[K]' is not assignable to type 'U[K] | undefined'.
   Type 'T[keyof T]' is not assignable to type 'U[K] | undefined'.
     Type 'T[string] | T[number] | T[symbol]' is not assignable to type 'U[K] | undefined'.
       Type 'T[string]' is not assignable to type 'U[K] | undefined'.
+        Type 'T[string]' is not assignable to type 'U[K]'.
+          Type 'T' is not assignable to type 'U'.
+            'U' could be instantiated with an arbitrary type which could be unrelated to 'T'.
 tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(51,5): error TS2542: Index signature in type 'Readonly<T>' only permits reading.
 tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(56,5): error TS2542: Index signature in type 'Readonly<T>' only permits reading.
 tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(61,5): error TS2322: Type 'T[keyof T]' is not assignable to type 'U[keyof T]'.
@@ -146,6 +152,10 @@ tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(168,5): error TS
 !!! error TS2322: Type 'T[keyof T]' is not assignable to type 'U[keyof T] | undefined'.
 !!! error TS2322:   Type 'T[string] | T[number] | T[symbol]' is not assignable to type 'U[keyof T] | undefined'.
 !!! error TS2322:     Type 'T[string]' is not assignable to type 'U[keyof T] | undefined'.
+!!! error TS2322:       Type 'T[string]' is not assignable to type 'U[keyof T]'.
+!!! error TS2322:         Type 'T' is not assignable to type 'U'.
+!!! error TS2322:           'U' could be instantiated with an arbitrary type which could be unrelated to 'T'.
+!!! related TS2208 tests/cases/conformance/types/mapped/mappedTypeRelationships.ts:39:14: This type parameter might need an `extends U` constraint.
     }
 
     function f13<T, U extends T, K extends keyof T>(x: T, y: Partial<U>, k: K) {
@@ -159,6 +169,10 @@ tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(168,5): error TS
 !!! error TS2322:   Type 'T[keyof T]' is not assignable to type 'U[K] | undefined'.
 !!! error TS2322:     Type 'T[string] | T[number] | T[symbol]' is not assignable to type 'U[K] | undefined'.
 !!! error TS2322:       Type 'T[string]' is not assignable to type 'U[K] | undefined'.
+!!! error TS2322:         Type 'T[string]' is not assignable to type 'U[K]'.
+!!! error TS2322:           Type 'T' is not assignable to type 'U'.
+!!! error TS2322:             'U' could be instantiated with an arbitrary type which could be unrelated to 'T'.
+!!! related TS2208 tests/cases/conformance/types/mapped/mappedTypeRelationships.ts:44:14: This type parameter might need an `extends U` constraint.
     }
 
     function f20<T>(x: T, y: Readonly<T>, k: keyof T) {

tests/baselines/reference/intersectionReduction.types

@@ -54,7 +54,7 @@ class B {
 >PropDeco : (target: Object, propKey: string | symbol) => void
 
     d: undefined | null;
->d : null
+>d : never
 >null : null
 
     @PropDeco

tests/baselines/reference/localTypeParameterInferencePriority.types

@@ -59,8 +59,8 @@ for (var a in x) {
 >b : any
 
     var c = a || b;
->c : string
->a || b : string
+>c : string | undefined
+>a || b : string | undefined
 >a : string
 >b : undefined
 }

tests/baselines/reference/mappedTypeRelationships.errors.txt

@@ -17,7 +17,7 @@ function test<T>(f1: Transform1<T>, f2: Transform2<T>) {
 
     f1?.("hello");
 >f1?.("hello") : T
->f1 : (value: string) => T
+>f1 : ((value: string) => T) | undefined
 >"hello" : "hello"
 
     f2?.("hello");
@@ -28,23 +28,23 @@ function test<T>(f1: Transform1<T>, f2: Transform2<T>) {
 
 function f1<T>(x: T | (string extends T ? null | undefined : never)) {
 >f1 : <T>(x: T | (string extends T ? null | undefined : never)) => void
->x : T | (string extends T ? null : never)
+>x : T | (string extends T ? never : never)
 >null : null
 
     let z = x!;  // NonNullable<T>
->z : T | (string extends T ? null : never)
->x! : T | (string extends T ? null : never)
->x : T | (string extends T ? null : never)
+>z : T
+>x! : T
+>x : T | (string extends T ? never : never)
 }
 
 function f2<T, U extends null | undefined>(x: T | U) {
->f2 : <T, U extends null>(x: T | U) => void
+>f2 : <T, U extends never>(x: T | U) => void
 >null : null
 >x : T | U
 
     let z = x!;  // NonNullable<T>
->z : T | U
->x! : T | U
+>z : T
+>x! : T
 >x : T | U
 }
 

tests/baselines/reference/metadataOfUnionWithNull.types

@@ -30,7 +30,7 @@ declare const a7: unknown | null
 >null : null
 
 declare const a8: never | null
->a8 : null
+>a8 : never
 >null : null
 
 declare const a9: any | null
@@ -81,9 +81,9 @@ const aa7 = a7 ?? 'whatever'
 >'whatever' : "whatever"
 
 const aa8 = a8 ?? 'whatever'
->aa8 : "whatever"
->a8 ?? 'whatever' : "whatever"
->a8 : null
+>aa8 : never
+>a8 ?? 'whatever' : never
+>a8 : never
 >'whatever' : "whatever"
 
 const aa9 = a9 ?? 'whatever'

tests/baselines/reference/noImplicitAnyForIn.types

@@ -1,5 +1,5 @@
 tests/cases/compiler/privateFieldAssignabilityFromUnknown.ts(2,3): error TS18028: Private identifiers are only available when targeting ECMAScript 2015 and higher.
-tests/cases/compiler/privateFieldAssignabilityFromUnknown.ts(5,7): error TS2741: Property '#field' is missing in type '{}' but required in type 'Class'.
+tests/cases/compiler/privateFieldAssignabilityFromUnknown.ts(5,7): error TS2322: Type 'unknown' is not assignable to type 'Class'.
 
 
 ==== tests/cases/compiler/privateFieldAssignabilityFromUnknown.ts (2 errors) ====
@@ -11,6 +11,5 @@ tests/cases/compiler/privateFieldAssignabilityFromUnknown.ts(5,7): error TS2741:
 
     const task: Class = {} as unknown;
           ~~~~
-!!! error TS2741: Property '#field' is missing in type '{}' but required in type 'Class'.
-!!! related TS2728 tests/cases/compiler/privateFieldAssignabilityFromUnknown.ts:2:3: '#field' is declared here.
+!!! error TS2322: Type 'unknown' is not assignable to type 'Class'.
 

tests/baselines/reference/nonNullableReductionNonStrict.types

@@ -72,7 +72,6 @@ var r3: string = a().toString();
 var r3b: string = a()['toString']();
 >r3b : Symbol(r3b, Decl(propertyAccessOnTypeParameterWithoutConstraints.ts, 21, 3))
 >a : Symbol(a, Decl(propertyAccessOnTypeParameterWithoutConstraints.ts, 17, 3))
->'toString' : Symbol(Object.toString, Decl(lib.es5.d.ts, --, --))
 
 var b = {
 >b : Symbol(b, Decl(propertyAccessOnTypeParameterWithoutConstraints.ts, 23, 3))