Type guard by deep property

src/compiler/sys.ts

@@ -1283,8 +1283,8 @@ namespace ts {
 
             const platform: string = _os.platform();
             const useCaseSensitiveFileNames = isFileSystemCaseSensitive();
-            const realpathSync = _fs.realpathSync.native ?? _fs.realpathSync;
-
+            // Use `any` to avoid type narrow.
+            const realpathSync = (_fs as any).realpathSync.native ?? _fs.realpathSync;
             const fsSupportsRecursiveFsWatch = isNode4OrLater && (process.platform === "win32" || process.platform === "darwin");
             const getCurrentDirectory = memoize(() => process.cwd());
             const { watchFile, watchDirectory } = createSystemWatchFunctions({

src/server/session.ts

@@ -1516,7 +1516,8 @@ namespace ts.server {
             // filter handles case when 'projects' is undefined
             projects = filter(projects, p => p.languageServiceEnabled && !p.isOrphan());
             if (!ignoreNoProjectError && (!projects || !projects.length) && !symLinkedProjects) {
-                this.projectService.logErrorForScriptInfoNotFound(args.file ?? args.projectFileName);
+                // use `any` to avoid type narrow
+                this.projectService.logErrorForScriptInfoNotFound((args as any).file ?? args.projectFileName);
                 return Errors.ThrowNoProject();
             }
             return symLinkedProjects ? { projects: projects!, symLinkedProjects } : projects!; // TODO: GH#18217

tests/baselines/reference/controlFlowOptionalChain.errors.txt

@@ -57,11 +57,10 @@ tests/cases/conformance/controlFlow/controlFlowOptionalChain.ts(463,9): error TS
 tests/cases/conformance/controlFlow/controlFlowOptionalChain.ts(498,13): error TS2532: Object is possibly 'undefined'.
 tests/cases/conformance/controlFlow/controlFlowOptionalChain.ts(501,13): error TS2532: Object is possibly 'undefined'.
 tests/cases/conformance/controlFlow/controlFlowOptionalChain.ts(515,13): error TS2532: Object is possibly 'undefined'.
-tests/cases/conformance/controlFlow/controlFlowOptionalChain.ts(518,13): error TS2532: Object is possibly 'undefined'.
 tests/cases/conformance/controlFlow/controlFlowOptionalChain.ts(567,21): error TS2532: Object is possibly 'undefined'.
 
 
-==== tests/cases/conformance/controlFlow/controlFlowOptionalChain.ts (61 errors) ====
+==== tests/cases/conformance/controlFlow/controlFlowOptionalChain.ts (60 errors) ====
     // assignments in shortcutting chain
     declare const o: undefined | {
         [key: string]: any;
@@ -697,9 +696,7 @@ tests/cases/conformance/controlFlow/controlFlowOptionalChain.ts(567,21): error T
 !!! error TS2532: Object is possibly 'undefined'.
                 break;
             default:
-                o.foo;  // Error
-                ~
-!!! error TS2532: Object is possibly 'undefined'.
+                o.foo;
                 break;
         }
     }

tests/baselines/reference/controlFlowOptionalChain.js

@@ -516,7 +516,7 @@ function f41(o: Thing | undefined) {
             o.foo;  // Error
             break;
         default:
-            o.foo;  // Error
+            o.foo;
             break;
     }
 }
@@ -1049,7 +1049,7 @@ function f41(o) {
             o.foo; // Error
             break;
         default:
-            o.foo; // Error
+            o.foo;
             break;
     }
 }

tests/baselines/reference/controlFlowOptionalChain.symbols

@@ -1438,9 +1438,7 @@ function f23(o: Thing | undefined) {
 >foo : Symbol(foo, Decl(controlFlowOptionalChain.ts, 161, 14))
 
         o.foo;  // Error
->o.foo : Symbol(foo, Decl(controlFlowOptionalChain.ts, 161, 14))
 >o : Symbol(o, Decl(controlFlowOptionalChain.ts, 439, 13))
->foo : Symbol(foo, Decl(controlFlowOptionalChain.ts, 161, 14))
     }
     else {
         o.foo;
@@ -1460,19 +1458,15 @@ function f23(o: Thing | undefined) {
     }
     else {
         o.foo;  // Error
->o.foo : Symbol(foo, Decl(controlFlowOptionalChain.ts, 161, 14))
 >o : Symbol(o, Decl(controlFlowOptionalChain.ts, 439, 13))
->foo : Symbol(foo, Decl(controlFlowOptionalChain.ts, 161, 14))
     }
     if (typeof o?.foo == "undefined") {
 >o?.foo : Symbol(foo, Decl(controlFlowOptionalChain.ts, 161, 14))
 >o : Symbol(o, Decl(controlFlowOptionalChain.ts, 439, 13))
 >foo : Symbol(foo, Decl(controlFlowOptionalChain.ts, 161, 14))
 
         o.foo;  // Error
->o.foo : Symbol(foo, Decl(controlFlowOptionalChain.ts, 161, 14))
 >o : Symbol(o, Decl(controlFlowOptionalChain.ts, 439, 13))
->foo : Symbol(foo, Decl(controlFlowOptionalChain.ts, 161, 14))
     }
     else {
         o.foo;
@@ -1492,9 +1486,7 @@ function f23(o: Thing | undefined) {
     }
     else {
         o.foo;  // Error
->o.foo : Symbol(foo, Decl(controlFlowOptionalChain.ts, 161, 14))
 >o : Symbol(o, Decl(controlFlowOptionalChain.ts, 439, 13))
->foo : Symbol(foo, Decl(controlFlowOptionalChain.ts, 161, 14))
     }
 }
 
@@ -1636,13 +1628,11 @@ function f41(o: Thing | undefined) {
             break;
         case "undefined":
             o.foo;  // Error
->o.foo : Symbol(foo, Decl(controlFlowOptionalChain.ts, 161, 14))
 >o : Symbol(o, Decl(controlFlowOptionalChain.ts, 505, 13))
->foo : Symbol(foo, Decl(controlFlowOptionalChain.ts, 161, 14))
 
             break;
         default:
-            o.foo;  // Error
+            o.foo;
 >o.foo : Symbol(foo, Decl(controlFlowOptionalChain.ts, 161, 14))
 >o : Symbol(o, Decl(controlFlowOptionalChain.ts, 505, 13))
 >foo : Symbol(foo, Decl(controlFlowOptionalChain.ts, 161, 14))

tests/baselines/reference/controlFlowOptionalChain.types

@@ -1618,9 +1618,9 @@ function f23(o: Thing | undefined) {
 >"undefined" : "undefined"
 
         o.foo;  // Error
->o.foo : never
->o : Thing | undefined
->foo : never
+>o.foo : any
+>o : undefined
+>foo : any
     }
     else {
         o.foo;
@@ -1643,9 +1643,9 @@ function f23(o: Thing | undefined) {
     }
     else {
         o.foo;  // Error
->o.foo : never
->o : Thing | undefined
->foo : never
+>o.foo : any
+>o : undefined
+>foo : any
     }
     if (typeof o?.foo == "undefined") {
 >typeof o?.foo == "undefined" : boolean
@@ -1656,9 +1656,9 @@ function f23(o: Thing | undefined) {
 >"undefined" : "undefined"
 
         o.foo;  // Error
->o.foo : never
->o : Thing | undefined
->foo : never
+>o.foo : any
+>o : undefined
+>foo : any
     }
     else {
         o.foo;
@@ -1681,9 +1681,9 @@ function f23(o: Thing | undefined) {
     }
     else {
         o.foo;  // Error
->o.foo : never
->o : Thing | undefined
->foo : never
+>o.foo : any
+>o : undefined
+>foo : any
     }
 }
 
@@ -1852,15 +1852,15 @@ function f41(o: Thing | undefined) {
 >"undefined" : "undefined"
 
             o.foo;  // Error
->o.foo : never
->o : Thing | undefined
->foo : never
+>o.foo : any
+>o : undefined
+>foo : any
 
             break;
         default:
-            o.foo;  // Error
+            o.foo;
 >o.foo : never
->o : Thing | undefined
+>o : Thing
 >foo : never
 
             break;

tests/baselines/reference/destructuringControlFlow.types

@@ -63,34 +63,34 @@ function f2(obj: [number, string] | null[]) {
 >obj[0] : number | null
 >obj : [number, string] | null[]
 >0 : 0
->obj[1] : string | null
->obj : [number, string] | null[]
+>obj[1] : string
+>obj : [number, string]
 >1 : 1
 
         let c0 = obj[0];  // number
 >c0 : number
 >obj[0] : number
->obj : [number, string] | null[]
+>obj : [number, string]
 >0 : 0
 
         let c1 = obj[1];  // string
 >c1 : string
 >obj[1] : string
->obj : [number, string] | null[]
+>obj : [number, string]
 >1 : 1
 
         let [d0, d1] = obj;
 >d0 : number
 >d1 : string
->obj : [number, string] | null[]
+>obj : [number, string]
 
         ([c0, c1] = obj);
->([c0, c1] = obj) : [number, string] | null[]
->[c0, c1] = obj : [number, string] | null[]
+>([c0, c1] = obj) : [number, string]
+>[c0, c1] = obj : [number, string]
 >[c0, c1] : [number, string]
 >c0 : number
 >c1 : string
->obj : [number, string] | null[]
+>obj : [number, string]
     }
 }
 

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;
@@ -142,7 +143,9 @@ tests/cases/conformance/types/union/discriminatedUnionTypes2.ts(32,11): error TS
             x.value;  // number
         }
         else {
-            x.value;  // number
+            x.value;  // Error, x is never
+              ~~~~~
+!!! error TS2339: Property 'value' does not exist on type 'never'.
         }
     }
 

tests/baselines/reference/discriminatedUnionTypes2.js

@@ -130,7 +130,7 @@ function foo1(x: RuntimeValue & { type: 'number' }) {
         x.value;  // number
     }
     else {
-        x.value;  // number
+        x.value;  // Error, x is never
     }
 }
 
@@ -226,7 +226,7 @@ function foo1(x) {
         x.value; // number
     }
     else {
-        x.value; // number
+        x.value; // Error, x is never
     }
 }
 function foo2(x) {

tests/baselines/reference/discriminatedUnionTypes2.symbols

@@ -366,10 +366,8 @@ function foo1(x: RuntimeValue & { type: 'number' }) {
 >value : Symbol(value, Decl(discriminatedUnionTypes2.ts, 122, 23))
     }
     else {
-        x.value;  // number
->x.value : Symbol(value, Decl(discriminatedUnionTypes2.ts, 122, 23))
+        x.value;  // Error, x is never
 >x : Symbol(x, Decl(discriminatedUnionTypes2.ts, 126, 14))
->value : Symbol(value, Decl(discriminatedUnionTypes2.ts, 122, 23))
     }
 }
 

tests/baselines/reference/discriminatedUnionTypes2.types

@@ -379,10 +379,10 @@ function foo1(x: RuntimeValue & { type: 'number' }) {
 >value : number
     }
     else {
-        x.value;  // number
->x.value : number
->x : { type: "number"; value: number; } & { type: "number"; }
->value : number
+        x.value;  // Error, x is never
+>x.value : any
+>x : never
+>value : any
     }
 }
 

tests/baselines/reference/discriminatedUnionTypes3.errors.txt

@@ -0,0 +1,91 @@
+tests/cases/conformance/types/union/discriminatedUnionTypes3.ts(59,11): error TS2339: Property 's' does not exist on type 'T'.
+tests/cases/conformance/types/union/discriminatedUnionTypes3.ts(78,10): error TS2339: Property 'property' does not exist on type 'SomeReturnType'.
+  Property 'property' does not exist on type 'Err'.
+
+
+==== tests/cases/conformance/types/union/discriminatedUnionTypes3.ts (2 errors) ====
+    type A = { type2: "a", a: number }
+    type B = { type2: "b", b: number }
+    type C = { type2: "c", b: number | string }
+
+    type X = { type1: A, x: string }
+    type Y = { type1: B, y: string }
+    type Z = { type1: C, z: string }
+    type W = { type1: undefined }
+
+    function f32(x: X | Y) {
+        switch (x.type1.type2) {
+            case "a":
+                x.x // typeof x is X
+                break;
+            case "b":
+                x.y // typeof x is Y
+                break;
+        }
+    }
+
+    function f33(x: A | B) {
+        switch (x.type2) {
+            case "a":
+                x // typeof x is X
+                break;
+            case "b":
+                x // typeof x is Y
+                break;
+        }
+    }
+
+    function f34(x: X | Y) {
+        if (x.type1.type2 === "a") {
+            x.x // typeof x is X
+        } else if (x.type1.type2 === "b") {
+            x.y // typeof x is Y
+        }
+    }
+
+    function f35(x: X | W) {
+        if (x.type1?.type2 === "a") {
+            x.x
+        }
+    }
+
+    function f36(x: X | W) {
+        x.type1?.type2 ?? x;
+    }
+
+    type S = { sub: { type0: X }, s: string }
+    type T = { sub: { type0: Y }, t: string }
+
+    function f37(s: S | T) {
+        if (s.sub.type0.type1.type2 === "a") {
+            s.s // typeof s is S
+            s.sub.type0.x // type of s.sub.type is X
+            s.sub.type0.type1.a // type of s.sub.type.type is A
+        } else {
+            s.s // type error!
+              ~
+!!! error TS2339: Property 's' does not exist on type 'T'.
+        }
+    }
+
+    // Repro from #44435
+
+    type Correct = {
+    	code: string
+    	property: true
+    	err: undefined
+    }
+    type Err = {
+    	err: `${string} is wrong!`
+    }
+    type SomeReturnType = Correct | Err;
+
+    const example: SomeReturnType = {} as SomeReturnType;
+
+    if (example.err === undefined) {
+    	example.property;  // true
+    	        ~~~~~~~~
+!!! error TS2339: Property 'property' does not exist on type 'SomeReturnType'.
+!!! error TS2339:   Property 'property' does not exist on type 'Err'.
+    }
+