Make type guard function types invariant in the type guarded for.

src/compiler/checker.ts

@@ -11883,7 +11883,10 @@ namespace ts {
                 }
             }
 
-            const related = compareTypes(source.type, target.type, reportErrors);
+            let related = compareTypes(source.type, target.type, reportErrors);
+            if (related) {
+                related &= compareTypes(target.type, source.type, reportErrors);
+            }
             if (related === Ternary.False && reportErrors) {
                 errorReporter!(Diagnostics.Type_predicate_0_is_not_assignable_to_1, typePredicateToString(source), typePredicateToString(target));
             }

src/services/documentHighlights.ts

@@ -75,7 +75,7 @@ namespace ts.DocumentHighlights {
             case SyntaxKind.SetKeyword:
                 return getFromAllDeclarations(isAccessor, [SyntaxKind.GetKeyword, SyntaxKind.SetKeyword]);
             case SyntaxKind.AwaitKeyword:
-                return useParent(node.parent, isAwaitExpression, getAsyncAndAwaitOccurrences);
+                return useParent<AwaitExpression>(node.parent, isAwaitExpression, getAsyncAndAwaitOccurrences);
             case SyntaxKind.AsyncKeyword:
                 return highlightSpans(getAsyncAndAwaitOccurrences(node));
             case SyntaxKind.YieldKeyword:

tests/baselines/reference/typeGuardFunctionErrors.js

@@ -50,6 +50,7 @@ function hasNonMathcingGenericType<T>(a: string): a is T[] {
 let a: A;
 let b: B;
 
+declare function isA(p1): p1 is A;
 declare function isB(p1): p1 is B;
 declare function isC(p1): p1 is C;
 declare function funA(p1: any, p2: any): p1 is B;
@@ -71,8 +72,10 @@ if (hasNoTypeGuard(a)) {
 }
 
 // Type predicate type is not assignable
-declare function acceptingDifferentSignatureTypeGuardFunction(p1: (p1) => p1 is B);
+declare function acceptingDifferentSignatureTypeGuardFunction(p1: (p1) => p1 is A);
 acceptingDifferentSignatureTypeGuardFunction(isC);
+declare function acceptingDifferentSignatureTypeGuardFunction2(p1: (p1) => p1 is C);
+acceptingDifferentSignatureTypeGuardFunction2(isA);
 
 // Boolean not assignable to type guard
 var assign1: (p1, p2) => p1 is A;
@@ -240,6 +243,7 @@ if (hasNoTypeGuard(a)) {
     a.propB;
 }
 acceptingDifferentSignatureTypeGuardFunction(isC);
+acceptingDifferentSignatureTypeGuardFunction2(isA);
 // Boolean not assignable to type guard
 var assign1;
 assign1 = function (p1, p2) {

tests/baselines/reference/typeGuardFunctionErrors.types

@@ -99,6 +99,10 @@ let a: A;
 let b: B;
 >b : B
 
+declare function isA(p1): p1 is A;
+>isA : (p1: any) => p1 is A
+>p1 : any
+
 declare function isB(p1): p1 is B;
 >isB : (p1: any) => p1 is B
 >p1 : any
@@ -154,16 +158,26 @@ if (hasNoTypeGuard(a)) {
 }
 
 // Type predicate type is not assignable
-declare function acceptingDifferentSignatureTypeGuardFunction(p1: (p1) => p1 is B);
->acceptingDifferentSignatureTypeGuardFunction : (p1: (p1: any) => p1 is B) => any
->p1 : (p1: any) => p1 is B
+declare function acceptingDifferentSignatureTypeGuardFunction(p1: (p1) => p1 is A);
+>acceptingDifferentSignatureTypeGuardFunction : (p1: (p1: any) => p1 is A) => any
+>p1 : (p1: any) => p1 is A
 >p1 : any
 
 acceptingDifferentSignatureTypeGuardFunction(isC);
 >acceptingDifferentSignatureTypeGuardFunction(isC) : any
->acceptingDifferentSignatureTypeGuardFunction : (p1: (p1: any) => p1 is B) => any
+>acceptingDifferentSignatureTypeGuardFunction : (p1: (p1: any) => p1 is A) => any
 >isC : (p1: any) => p1 is C
 
+declare function acceptingDifferentSignatureTypeGuardFunction2(p1: (p1) => p1 is C);
+>acceptingDifferentSignatureTypeGuardFunction2 : (p1: (p1: any) => p1 is C) => any
+>p1 : (p1: any) => p1 is C
+>p1 : any
+
+acceptingDifferentSignatureTypeGuardFunction2(isA);
+>acceptingDifferentSignatureTypeGuardFunction2(isA) : any
+>acceptingDifferentSignatureTypeGuardFunction2 : (p1: (p1: any) => p1 is C) => any
+>isA : (p1: any) => p1 is A
+
 // Boolean not assignable to type guard
 var assign1: (p1, p2) => p1 is A;
 >assign1 : (p1: any, p2: any) => p1 is A

tests/baselines/reference/typeGuardOfFormThisMember.errors.txt

@@ -35,8 +35,8 @@ tests/cases/conformance/expressions/typeGuards/typeGuardOfFormThisMember.ts(79,1
 !!! error TS1228: A type predicate is only allowed in return type position for functions and methods.
     			return this instanceof Directory;
     		}
-    		isNetworked: this is (Networked & this);
-    		             ~~~~~~~~~~~~~~~~~~~~~~~~~~
+    		isNetworked: this is Networked;
+    		             ~~~~~~~~~~~~~~~~~
 !!! error TS1228: A type predicate is only allowed in return type position for functions and methods.
     		constructor(public path: string) {}
     	}

tests/baselines/reference/typeGuardOfFormThisMember.js

@@ -12,7 +12,7 @@ namespace Test {
 		get isDirectory(): this is Directory {
 			return this instanceof Directory;
 		}
-		isNetworked: this is (Networked & this);
+		isNetworked: this is Networked;
 		constructor(public path: string) {}
 	}
 
@@ -180,7 +180,7 @@ declare namespace Test {
         isFSO: this is FileSystemObject;
         isFile: this is File;
         readonly isDirectory: this is Directory;
-        isNetworked: this is (Networked & this);
+        isNetworked: this is Networked;
         constructor(path: string);
     }
     class File extends FileSystemObject {

tests/baselines/reference/typeGuardOfFormThisMember.symbols

@@ -32,7 +32,7 @@ namespace Test {
 >this : Symbol(FileSystemObject, Decl(typeGuardOfFormThisMember.ts, 1, 16))
 >Directory : Symbol(Directory, Decl(typeGuardOfFormThisMember.ts, 19, 2))
 		}
-		isNetworked: this is (Networked & this);
+		isNetworked: this is Networked;
 >isNetworked : Symbol(FileSystemObject.isNetworked, Decl(typeGuardOfFormThisMember.ts, 12, 3))
 >Networked : Symbol(Networked, Decl(typeGuardOfFormThisMember.ts, 22, 2))
 

tests/baselines/reference/typeGuardOfFormThisMember.types

@@ -31,7 +31,7 @@ namespace Test {
 >this : this
 >Directory : typeof Directory
 		}
-		isNetworked: this is (Networked & this);
+		isNetworked: this is Networked;
 >isNetworked : boolean
 
 		constructor(public path: string) {}

tests/baselines/reference/typeGuardOfFormThisMemberErrors.errors.txt

@@ -24,8 +24,8 @@ tests/cases/conformance/expressions/typeGuards/typeGuardOfFormThisMemberErrors.t
 !!! error TS1228: A type predicate is only allowed in return type position for functions and methods.
     			return this instanceof Directory;
     		}
-    		isNetworked: this is (Networked & this);
-    		             ~~~~~~~~~~~~~~~~~~~~~~~~~~
+    		isNetworked: this is Networked;
+    		             ~~~~~~~~~~~~~~~~~
 !!! error TS1228: A type predicate is only allowed in return type position for functions and methods.
     		constructor(public path: string) {}
     	}

tests/baselines/reference/typeGuardOfFormThisMemberErrors.js

@@ -12,7 +12,7 @@ namespace Test {
 		get isDirectory(): this is Directory {
 			return this instanceof Directory;
 		}
-		isNetworked: this is (Networked & this);
+		isNetworked: this is Networked;
 		constructor(public path: string) {}
 	}
 
@@ -105,7 +105,7 @@ declare namespace Test {
         isFSO: this is FileSystemObject;
         isFile: this is File;
         readonly isDirectory: this is Directory;
-        isNetworked: this is (Networked & this);
+        isNetworked: this is Networked;
         constructor(path: string);
     }
     class File extends FileSystemObject {

tests/baselines/reference/typeGuardOfFormThisMemberErrors.symbols

@@ -32,7 +32,7 @@ namespace Test {
 >this : Symbol(FileSystemObject, Decl(typeGuardOfFormThisMemberErrors.ts, 1, 16))
 >Directory : Symbol(Directory, Decl(typeGuardOfFormThisMemberErrors.ts, 19, 2))
 		}
-		isNetworked: this is (Networked & this);
+		isNetworked: this is Networked;
 >isNetworked : Symbol(FileSystemObject.isNetworked, Decl(typeGuardOfFormThisMemberErrors.ts, 12, 3))
 >Networked : Symbol(Networked, Decl(typeGuardOfFormThisMemberErrors.ts, 22, 2))
 

tests/baselines/reference/typeGuardOfFormThisMemberErrors.types

@@ -31,7 +31,7 @@ namespace Test {
 >this : this
 >Directory : typeof Directory
 		}
-		isNetworked: this is (Networked & this);
+		isNetworked: this is Networked;
 >isNetworked : boolean
 
 		constructor(public path: string) {}

tests/cases/conformance/expressions/typeGuards/typeGuardFunctionErrors.ts

@@ -50,6 +50,7 @@ function hasNonMathcingGenericType<T>(a: string): a is T[] {
 let a: A;
 let b: B;
 
+declare function isA(p1): p1 is A;
 declare function isB(p1): p1 is B;
 declare function isC(p1): p1 is C;
 declare function funA(p1: any, p2: any): p1 is B;
@@ -71,8 +72,10 @@ if (hasNoTypeGuard(a)) {
 }
 
 // Type predicate type is not assignable
-declare function acceptingDifferentSignatureTypeGuardFunction(p1: (p1) => p1 is B);
+declare function acceptingDifferentSignatureTypeGuardFunction(p1: (p1) => p1 is A);
 acceptingDifferentSignatureTypeGuardFunction(isC);
+declare function acceptingDifferentSignatureTypeGuardFunction2(p1: (p1) => p1 is C);
+acceptingDifferentSignatureTypeGuardFunction2(isA);
 
 // Boolean not assignable to type guard
 var assign1: (p1, p2) => p1 is A;

tests/cases/conformance/expressions/typeGuards/typeGuardOfFormThisMember.ts

@@ -13,7 +13,7 @@ namespace Test {
 		get isDirectory(): this is Directory {
 			return this instanceof Directory;
 		}
-		isNetworked: this is (Networked & this);
+		isNetworked: this is Networked;
 		constructor(public path: string) {}
 	}
 

tests/cases/conformance/expressions/typeGuards/typeGuardOfFormThisMemberErrors.ts

@@ -13,7 +13,7 @@ namespace Test {
 		get isDirectory(): this is Directory {
 			return this instanceof Directory;
 		}
-		isNetworked: this is (Networked & this);
+		isNetworked: this is Networked;
 		constructor(public path: string) {}
 	}
 

tests/cases/fourslash/thisPredicateFunctionCompletions01.ts

@@ -7,7 +7,7 @@
 ////     isDirectory(): this is Directory {
 ////         return this instanceof Directory;
 ////     }
-////     isNetworked(): this is (Networked & this) {
+////     isNetworked(): this is Networked {
 ////        return !!(this as Networked).host;
 ////     }
 ////     constructor(public path: string) {}
@@ -43,8 +43,8 @@
 const common: ReadonlyArray<string> = ["isFile", "isDirectory", "isNetworked", "path"];
 verify.completions(
     { marker: "1", exact: ["content", ...common] },
-    { marker: "2", exact: ["host", "content", ...common] },
+    { marker: "2", exact: ["content", ...common, "host"] },
     { marker: "3", exact: ["children", ...common] },
-    { marker: "4", exact: ["host", "children", ...common] },
-    { marker: "5", exact: ["host", ...common] },
+    { marker: "4", exact: ["children", ...common, "host"] },
+    { marker: "5", exact: [...common, "host"] },
 );

tests/cases/fourslash/thisPredicateFunctionCompletions02.ts

@@ -12,7 +12,7 @@
 ////     contents: T;
 ////     isSundries(): this is Crate<Sundries>;
 ////     isSupplies(): this is Crate<Supplies>;
-////     isPackedTight(): this is (this & {extraContents: T});
+////     isPackedTight<U>(this: this & Crate<U>): this is {extraContents: U};
 //// }
 //// const crate: Crate<any>;
 //// if (crate.isPackedTight()) {

tests/cases/fourslash/thisPredicateFunctionQuickInfo01.ts

@@ -7,7 +7,7 @@
 ////     /*2*/isDirectory(): this is Directory {
 ////         return this instanceof Directory;
 ////     }
-////     /*3*/isNetworked(): this is (Networked & this) {
+////     /*3*/isNetworked(): this is Networked {
 ////        return !!(this as Networked).host;
 ////     }
 ////     constructor(public path: string) {}
@@ -43,11 +43,11 @@
 verify.quickInfos({
     1: "(method) FileSystemObject.isFile(): this is Item",
     2: "(method) FileSystemObject.isDirectory(): this is Directory",
-    3: "(method) FileSystemObject.isNetworked(): this is Networked & this",
+    3: "(method) FileSystemObject.isNetworked(): this is Networked",
 
     4: "(method) FileSystemObject.isFile(): this is Item",
-    5: "(method) FileSystemObject.isNetworked(): this is Networked & Item",
+    5: "(method) FileSystemObject.isNetworked(): this is Networked",
     6: "(method) FileSystemObject.isDirectory(): this is Directory",
-    7: "(method) FileSystemObject.isNetworked(): this is Networked & Directory",
-    8: "(method) FileSystemObject.isNetworked(): this is Networked & FileSystemObject"
+    7: "(method) FileSystemObject.isNetworked(): this is Networked",
+    8: "(method) FileSystemObject.isNetworked(): this is Networked"
 });

tests/cases/fourslash/thisPredicateFunctionQuickInfo02.ts

@@ -12,7 +12,7 @@
 ////     contents: T;
 ////     /*1*/isSundries(): this is Crate<Sundries>;
 ////     /*2*/isSupplies(): this is Crate<Supplies>;
-////     /*3*/isPackedTight(): this is (this & {extraContents: T});
+////     /*3*/isPackedTight<U>(this: this & Crate<U>): this is {extraContents: U};
 //// }
 //// const crate: Crate<any>;
 //// if (crate.isPackedTight/*4*/()) {
@@ -34,18 +34,18 @@
 verify.quickInfos({
     1: "(method) Crate<T>.isSundries(): this is Crate<Sundries>",
     2: "(method) Crate<T>.isSupplies(): this is Crate<Supplies>",
-    3: `(method) Crate<T>.isPackedTight(): this is this & {
-    extraContents: T;
+    3: `(method) Crate<T>.isPackedTight<U>(this: this & Crate<U>): this is {
+    extraContents: U;
 }`,
-    4: `(method) Crate<any>.isPackedTight(): this is Crate<any> & {
+    4: `(method) Crate<any>.isPackedTight<any>(this: Crate<any>): this is {
     extraContents: any;
 }`,
     5: "(method) Crate<any>.isSundries(): this is Crate<Sundries>",
-    6: `(method) Crate<Sundries>.isPackedTight(): this is Crate<Sundries> & {
+    6: `(method) Crate<Sundries>.isPackedTight<Sundries>(this: Crate<Sundries>): this is {
     extraContents: Sundries;
 }`,
     7: "(method) Crate<any>.isSupplies(): this is Crate<Supplies>",
-    8: `(method) Crate<Supplies>.isPackedTight(): this is Crate<Supplies> & {
+    8: `(method) Crate<Supplies>.isPackedTight<Supplies>(this: Crate<Supplies>): this is {
     extraContents: Supplies;
 }`
 });