Add tests

tests/baselines/reference/intersectionsAndOptionalProperties.errors.txt

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+tests/cases/compiler/intersectionsAndOptionalProperties.ts(5,1): error TS2322: Type '{ a: null; b: string; }' is not assignable to type '{ a?: number | undefined; b: string; }'.
+  Types of property 'a' are incompatible.
+    Type 'null' is not assignable to type 'number | undefined'.
+tests/cases/compiler/intersectionsAndOptionalProperties.ts(6,1): error TS2322: Type '{ a: null; } & { b: string; }' is not assignable to type '{ a?: number | undefined; b: string; }'.
+  Types of property 'a' are incompatible.
+    Type 'null' is not assignable to type 'number | undefined'.
+tests/cases/compiler/intersectionsAndOptionalProperties.ts(19,5): error TS2322: Type 'From' is not assignable to type 'To'.
+  Types of property 'field' are incompatible.
+    Type 'null' is not assignable to type 'number | undefined'.
+tests/cases/compiler/intersectionsAndOptionalProperties.ts(20,5): error TS2322: Type 'null' is not assignable to type 'number | undefined'.
+
+
+==== tests/cases/compiler/intersectionsAndOptionalProperties.ts (4 errors) ====
+    declare let x: { a?: number, b: string };
+    declare let y: { a: null, b: string };
+    declare let z: { a: null } & { b: string };
+
+    x = y;  // Error
+    ~
+!!! error TS2322: Type '{ a: null; b: string; }' is not assignable to type '{ a?: number | undefined; b: string; }'.
+!!! error TS2322:   Types of property 'a' are incompatible.
+!!! error TS2322:     Type 'null' is not assignable to type 'number | undefined'.
+    x = z;  // Error
+    ~
+!!! error TS2322: Type '{ a: null; } & { b: string; }' is not assignable to type '{ a?: number | undefined; b: string; }'.
+!!! error TS2322:   Types of property 'a' are incompatible.
+!!! error TS2322:     Type 'null' is not assignable to type 'number | undefined'.
+
+    // Repro from #36604
+
+    interface To {
+        field?: number;
+        anotherField: string;
+    }
+
+    type From =  { field: null } & Omit<To, 'field'>;
+
+    function foo(v: From) {
+        let x: To;
+        x = v;  // Error
+        ~
+!!! error TS2322: Type 'From' is not assignable to type 'To'.
+!!! error TS2322:   Types of property 'field' are incompatible.
+!!! error TS2322:     Type 'null' is not assignable to type 'number | undefined'.
+        x.field = v.field; // Error
+        ~~~~~~~
+!!! error TS2322: Type 'null' is not assignable to type 'number | undefined'.
+    }
+

tests/baselines/reference/intersectionsAndOptionalProperties.js

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+//// [intersectionsAndOptionalProperties.ts]
+declare let x: { a?: number, b: string };
+declare let y: { a: null, b: string };
+declare let z: { a: null } & { b: string };
+
+x = y;  // Error
+x = z;  // Error
+
+// Repro from #36604
+
+interface To {
+    field?: number;
+    anotherField: string;
+}
+
+type From =  { field: null } & Omit<To, 'field'>;
+
+function foo(v: From) {
+    let x: To;
+    x = v;  // Error
+    x.field = v.field; // Error
+}
+
+
+//// [intersectionsAndOptionalProperties.js]
+"use strict";
+x = y; // Error
+x = z; // Error
+function foo(v) {
+    var x;
+    x = v; // Error
+    x.field = v.field; // Error
+}

tests/baselines/reference/intersectionsAndOptionalProperties.symbols

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+=== tests/cases/compiler/intersectionsAndOptionalProperties.ts ===
+declare let x: { a?: number, b: string };
+>x : Symbol(x, Decl(intersectionsAndOptionalProperties.ts, 0, 11))
+>a : Symbol(a, Decl(intersectionsAndOptionalProperties.ts, 0, 16))
+>b : Symbol(b, Decl(intersectionsAndOptionalProperties.ts, 0, 28))
+
+declare let y: { a: null, b: string };
+>y : Symbol(y, Decl(intersectionsAndOptionalProperties.ts, 1, 11))
+>a : Symbol(a, Decl(intersectionsAndOptionalProperties.ts, 1, 16))
+>b : Symbol(b, Decl(intersectionsAndOptionalProperties.ts, 1, 25))
+
+declare let z: { a: null } & { b: string };
+>z : Symbol(z, Decl(intersectionsAndOptionalProperties.ts, 2, 11))
+>a : Symbol(a, Decl(intersectionsAndOptionalProperties.ts, 2, 16))
+>b : Symbol(b, Decl(intersectionsAndOptionalProperties.ts, 2, 30))
+
+x = y;  // Error
+>x : Symbol(x, Decl(intersectionsAndOptionalProperties.ts, 0, 11))
+>y : Symbol(y, Decl(intersectionsAndOptionalProperties.ts, 1, 11))
+
+x = z;  // Error
+>x : Symbol(x, Decl(intersectionsAndOptionalProperties.ts, 0, 11))
+>z : Symbol(z, Decl(intersectionsAndOptionalProperties.ts, 2, 11))
+
+// Repro from #36604
+
+interface To {
+>To : Symbol(To, Decl(intersectionsAndOptionalProperties.ts, 5, 6))
+
+    field?: number;
+>field : Symbol(To.field, Decl(intersectionsAndOptionalProperties.ts, 9, 14))
+
+    anotherField: string;
+>anotherField : Symbol(To.anotherField, Decl(intersectionsAndOptionalProperties.ts, 10, 19))
+}
+
+type From =  { field: null } & Omit<To, 'field'>;
+>From : Symbol(From, Decl(intersectionsAndOptionalProperties.ts, 12, 1))
+>field : Symbol(field, Decl(intersectionsAndOptionalProperties.ts, 14, 14))
+>Omit : Symbol(Omit, Decl(lib.es5.d.ts, --, --))
+>To : Symbol(To, Decl(intersectionsAndOptionalProperties.ts, 5, 6))
+
+function foo(v: From) {
+>foo : Symbol(foo, Decl(intersectionsAndOptionalProperties.ts, 14, 49))
+>v : Symbol(v, Decl(intersectionsAndOptionalProperties.ts, 16, 13))
+>From : Symbol(From, Decl(intersectionsAndOptionalProperties.ts, 12, 1))
+
+    let x: To;
+>x : Symbol(x, Decl(intersectionsAndOptionalProperties.ts, 17, 7))
+>To : Symbol(To, Decl(intersectionsAndOptionalProperties.ts, 5, 6))
+
+    x = v;  // Error
+>x : Symbol(x, Decl(intersectionsAndOptionalProperties.ts, 17, 7))
+>v : Symbol(v, Decl(intersectionsAndOptionalProperties.ts, 16, 13))
+
+    x.field = v.field; // Error
+>x.field : Symbol(To.field, Decl(intersectionsAndOptionalProperties.ts, 9, 14))
+>x : Symbol(x, Decl(intersectionsAndOptionalProperties.ts, 17, 7))
+>field : Symbol(To.field, Decl(intersectionsAndOptionalProperties.ts, 9, 14))
+>v.field : Symbol(field, Decl(intersectionsAndOptionalProperties.ts, 14, 14))
+>v : Symbol(v, Decl(intersectionsAndOptionalProperties.ts, 16, 13))
+>field : Symbol(field, Decl(intersectionsAndOptionalProperties.ts, 14, 14))
+}
+

tests/baselines/reference/intersectionsAndOptionalProperties.types

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+=== tests/cases/compiler/intersectionsAndOptionalProperties.ts ===
+declare let x: { a?: number, b: string };
+>x : { a?: number | undefined; b: string; }
+>a : number | undefined
+>b : string
+
+declare let y: { a: null, b: string };
+>y : { a: null; b: string; }
+>a : null
+>null : null
+>b : string
+
+declare let z: { a: null } & { b: string };
+>z : { a: null; } & { b: string; }
+>a : null
+>null : null
+>b : string
+
+x = y;  // Error
+>x = y : { a: null; b: string; }
+>x : { a?: number | undefined; b: string; }
+>y : { a: null; b: string; }
+
+x = z;  // Error
+>x = z : { a: null; } & { b: string; }
+>x : { a?: number | undefined; b: string; }
+>z : { a: null; } & { b: string; }
+
+// Repro from #36604
+
+interface To {
+    field?: number;
+>field : number | undefined
+
+    anotherField: string;
+>anotherField : string
+}
+
+type From =  { field: null } & Omit<To, 'field'>;
+>From : From
+>field : null
+>null : null
+
+function foo(v: From) {
+>foo : (v: From) => void
+>v : From
+
+    let x: To;
+>x : To
+
+    x = v;  // Error
+>x = v : From
+>x : To
+>v : From
+
+    x.field = v.field; // Error
+>x.field = v.field : null
+>x.field : number | undefined
+>x : To
+>field : number | undefined
+>v.field : null
+>v : From
+>field : null
+}
+

tests/cases/compiler/intersectionsAndOptionalProperties.ts

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+// @strict: true
+
+declare let x: { a?: number, b: string };
+declare let y: { a: null, b: string };
+declare let z: { a: null } & { b: string };
+
+x = y;  // Error
+x = z;  // Error
+
+// Repro from #36604
+
+interface To {
+    field?: number;
+    anotherField: string;
+}
+
+type From =  { field: null } & Omit<To, 'field'>;
+
+function foo(v: From) {
+    let x: To;
+    x = v;  // Error
+    x.field = v.field; // Error
+}