Fixed an issue with in not being able to be used on narrowed down expression of a generic nullable type

src/compiler/checker.ts

@@ -34167,7 +34167,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
     }
 
     function hasEmptyObjectIntersection(type: Type): boolean {
-        return someType(type, t => t === unknownEmptyObjectType || !!(t.flags & TypeFlags.Intersection) && some((t as IntersectionType).types, isEmptyAnonymousObjectType));
+        return someType(type, t => t === unknownEmptyObjectType || !!(t.flags & TypeFlags.Intersection) && isEmptyAnonymousObjectType(getBaseConstraintOrType(t)));
     }
 
     function checkInExpression(left: Expression, right: Expression, leftType: Type, rightType: Type): Type {

tests/baselines/reference/inKeywordTypeguard(strict=false).errors.txt

@@ -420,4 +420,16 @@ tests/cases/compiler/inKeywordTypeguard.ts(186,21): error TS2322: Type 'T' is no
 
     const checkIsTouchDevice = () =>
         "ontouchstart" in window || "msMaxTouchPoints" in window.navigator;
+
+    // Repro from #51501
+
+    function isHTMLTable<T extends object | null>(table: T): boolean {
+        return !!table && 'html' in table;
+    }
+
+    // Repro from #51549
+
+    const f = <P extends object>(a: P & {}) => {
+        "foo" in a;
+    };
 

tests/baselines/reference/inKeywordTypeguard(strict=false).js

@@ -341,6 +341,18 @@ function foo<A>(value: A) {
 
 const checkIsTouchDevice = () =>
     "ontouchstart" in window || "msMaxTouchPoints" in window.navigator;
+
+// Repro from #51501
+
+function isHTMLTable<T extends object | null>(table: T): boolean {
+    return !!table && 'html' in table;
+}
+
+// Repro from #51549
+
+const f = <P extends object>(a: P & {}) => {
+    "foo" in a;
+};
 
 
 //// [inKeywordTypeguard.js]
@@ -655,3 +667,11 @@ function foo(value) {
 }
 // Repro from #50954
 const checkIsTouchDevice = () => "ontouchstart" in window || "msMaxTouchPoints" in window.navigator;
+// Repro from #51501
+function isHTMLTable(table) {
+    return !!table && 'html' in table;
+}
+// Repro from #51549
+const f = (a) => {
+    "foo" in a;
+};

tests/baselines/reference/inKeywordTypeguard(strict=false).symbols

@@ -853,3 +853,29 @@ const checkIsTouchDevice = () =>
 >window : Symbol(window, Decl(lib.dom.d.ts, --, --))
 >navigator : Symbol(navigator, Decl(lib.dom.d.ts, --, --), Decl(lib.dom.d.ts, --, --))
 
+// Repro from #51501
+
+function isHTMLTable<T extends object | null>(table: T): boolean {
+>isHTMLTable : Symbol(isHTMLTable, Decl(inKeywordTypeguard.ts, 341, 71))
+>T : Symbol(T, Decl(inKeywordTypeguard.ts, 345, 21))
+>table : Symbol(table, Decl(inKeywordTypeguard.ts, 345, 46))
+>T : Symbol(T, Decl(inKeywordTypeguard.ts, 345, 21))
+
+    return !!table && 'html' in table;
+>table : Symbol(table, Decl(inKeywordTypeguard.ts, 345, 46))
+>table : Symbol(table, Decl(inKeywordTypeguard.ts, 345, 46))
+}
+
+// Repro from #51549
+
+const f = <P extends object>(a: P & {}) => {
+>f : Symbol(f, Decl(inKeywordTypeguard.ts, 351, 5))
+>P : Symbol(P, Decl(inKeywordTypeguard.ts, 351, 11))
+>a : Symbol(a, Decl(inKeywordTypeguard.ts, 351, 29))
+>P : Symbol(P, Decl(inKeywordTypeguard.ts, 351, 11))
+
+    "foo" in a;
+>a : Symbol(a, Decl(inKeywordTypeguard.ts, 351, 29))
+
+};
+

tests/baselines/reference/inKeywordTypeguard(strict=false).types

@@ -1056,3 +1056,34 @@ const checkIsTouchDevice = () =>
 >window : Window & typeof globalThis
 >navigator : Navigator
 
+// Repro from #51501
+
+function isHTMLTable<T extends object | null>(table: T): boolean {
+>isHTMLTable : <T extends object>(table: T) => boolean
+>null : null
+>table : T
+
+    return !!table && 'html' in table;
+>!!table && 'html' in table : boolean
+>!!table : boolean
+>!table : boolean
+>table : T
+>'html' in table : boolean
+>'html' : "html"
+>table : T
+}
+
+// Repro from #51549
+
+const f = <P extends object>(a: P & {}) => {
+>f : <P extends object>(a: P & {}) => void
+><P extends object>(a: P & {}) => {    "foo" in a;} : <P extends object>(a: P & {}) => void
+>a : P & {}
+
+    "foo" in a;
+>"foo" in a : boolean
+>"foo" : "foo"
+>a : P & {}
+
+};
+

tests/baselines/reference/inKeywordTypeguard(strict=true).errors.txt

@@ -440,4 +440,16 @@ tests/cases/compiler/inKeywordTypeguard.ts(186,21): error TS2638: Type 'NonNulla
 
     const checkIsTouchDevice = () =>
         "ontouchstart" in window || "msMaxTouchPoints" in window.navigator;
+
+    // Repro from #51501
+
+    function isHTMLTable<T extends object | null>(table: T): boolean {
+        return !!table && 'html' in table;
+    }
+
+    // Repro from #51549
+
+    const f = <P extends object>(a: P & {}) => {
+        "foo" in a;
+    };
 

tests/baselines/reference/inKeywordTypeguard(strict=true).js

@@ -341,6 +341,18 @@ function foo<A>(value: A) {
 
 const checkIsTouchDevice = () =>
     "ontouchstart" in window || "msMaxTouchPoints" in window.navigator;
+
+// Repro from #51501
+
+function isHTMLTable<T extends object | null>(table: T): boolean {
+    return !!table && 'html' in table;
+}
+
+// Repro from #51549
+
+const f = <P extends object>(a: P & {}) => {
+    "foo" in a;
+};
 
 
 //// [inKeywordTypeguard.js]
@@ -656,3 +668,11 @@ function foo(value) {
 }
 // Repro from #50954
 const checkIsTouchDevice = () => "ontouchstart" in window || "msMaxTouchPoints" in window.navigator;
+// Repro from #51501
+function isHTMLTable(table) {
+    return !!table && 'html' in table;
+}
+// Repro from #51549
+const f = (a) => {
+    "foo" in a;
+};

tests/baselines/reference/inKeywordTypeguard(strict=true).symbols

@@ -853,3 +853,29 @@ const checkIsTouchDevice = () =>
 >window : Symbol(window, Decl(lib.dom.d.ts, --, --))
 >navigator : Symbol(navigator, Decl(lib.dom.d.ts, --, --), Decl(lib.dom.d.ts, --, --))
 
+// Repro from #51501
+
+function isHTMLTable<T extends object | null>(table: T): boolean {
+>isHTMLTable : Symbol(isHTMLTable, Decl(inKeywordTypeguard.ts, 341, 71))
+>T : Symbol(T, Decl(inKeywordTypeguard.ts, 345, 21))
+>table : Symbol(table, Decl(inKeywordTypeguard.ts, 345, 46))
+>T : Symbol(T, Decl(inKeywordTypeguard.ts, 345, 21))
+
+    return !!table && 'html' in table;
+>table : Symbol(table, Decl(inKeywordTypeguard.ts, 345, 46))
+>table : Symbol(table, Decl(inKeywordTypeguard.ts, 345, 46))
+}
+
+// Repro from #51549
+
+const f = <P extends object>(a: P & {}) => {
+>f : Symbol(f, Decl(inKeywordTypeguard.ts, 351, 5))
+>P : Symbol(P, Decl(inKeywordTypeguard.ts, 351, 11))
+>a : Symbol(a, Decl(inKeywordTypeguard.ts, 351, 29))
+>P : Symbol(P, Decl(inKeywordTypeguard.ts, 351, 11))
+
+    "foo" in a;
+>a : Symbol(a, Decl(inKeywordTypeguard.ts, 351, 29))
+
+};
+

tests/baselines/reference/inKeywordTypeguard(strict=true).types

@@ -1056,3 +1056,34 @@ const checkIsTouchDevice = () =>
 >window : Window & typeof globalThis
 >navigator : Navigator
 
+// Repro from #51501
+
+function isHTMLTable<T extends object | null>(table: T): boolean {
+>isHTMLTable : <T extends object | null>(table: T) => boolean
+>null : null
+>table : T
+
+    return !!table && 'html' in table;
+>!!table && 'html' in table : boolean
+>!!table : boolean
+>!table : boolean
+>table : T
+>'html' in table : boolean
+>'html' : "html"
+>table : NonNullable<T>
+}
+
+// Repro from #51549
+
+const f = <P extends object>(a: P & {}) => {
+>f : <P extends object>(a: P & {}) => void
+><P extends object>(a: P & {}) => {    "foo" in a;} : <P extends object>(a: P & {}) => void
+>a : P & {}
+
+    "foo" in a;
+>"foo" in a : boolean
+>"foo" : "foo"
+>a : P & {}
+
+};
+

tests/cases/compiler/inKeywordTypeguard.ts

@@ -343,3 +343,15 @@ function foo<A>(value: A) {
 
 const checkIsTouchDevice = () =>
     "ontouchstart" in window || "msMaxTouchPoints" in window.navigator;
+
+// Repro from #51501
+
+function isHTMLTable<T extends object | null>(table: T): boolean {
+    return !!table && 'html' in table;
+}
+
+// Repro from #51549
+
+const f = <P extends object>(a: P & {}) => {
+    "foo" in a;
+};