fix: [Symbol.iterator]() lost on union with never

src/compiler/checker.ts

@@ -45830,6 +45830,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
      * the `[Symbol.asyncIterator]()` method first, and then the `[Symbol.iterator]()` method.
      */
     function getIterationTypesOfIterable(type: Type, use: IterationUse, errorNode: Node | undefined) {
+        type = getReducedType(type);
         if (type === silentNeverType) {
             return silentNeverIterationTypes;
         }

tests/baselines/reference/iterableWithNeverAsUnionMember(target=es5).symbols

@@ -0,0 +1,94 @@
+//// [tests/cases/compiler/iterableWithNeverAsUnionMember.ts] ////
+
+=== iterableWithNeverAsUnionMember.ts ===
+declare const o1: { a: "foo" } & { a: "bar" };
+>o1 : Symbol(o1, Decl(iterableWithNeverAsUnionMember.ts, 0, 13))
+>a : Symbol(a, Decl(iterableWithNeverAsUnionMember.ts, 0, 19))
+>a : Symbol(a, Decl(iterableWithNeverAsUnionMember.ts, 0, 34))
+
+const [el1] = o1; // error
+>el1 : Symbol(el1, Decl(iterableWithNeverAsUnionMember.ts, 1, 7))
+>o1 : Symbol(o1, Decl(iterableWithNeverAsUnionMember.ts, 0, 13))
+
+// https://github.com/microsoft/TypeScript/issues/62462
+declare var x: number[] | ({ t: "a" } & { t: "b" });
+>x : Symbol(x, Decl(iterableWithNeverAsUnionMember.ts, 4, 11))
+>t : Symbol(t, Decl(iterableWithNeverAsUnionMember.ts, 4, 28))
+>t : Symbol(t, Decl(iterableWithNeverAsUnionMember.ts, 4, 41))
+
+let [el2] = x; // ok
+>el2 : Symbol(el2, Decl(iterableWithNeverAsUnionMember.ts, 5, 5))
+>x : Symbol(x, Decl(iterableWithNeverAsUnionMember.ts, 4, 11))
+
+for (const elem of x) { // ok
+>elem : Symbol(elem, Decl(iterableWithNeverAsUnionMember.ts, 7, 10))
+>x : Symbol(x, Decl(iterableWithNeverAsUnionMember.ts, 4, 11))
+
+  elem.toFixed();
+>elem.toFixed : Symbol(Number.toFixed, Decl(lib.es5.d.ts, --, --))
+>elem : Symbol(elem, Decl(iterableWithNeverAsUnionMember.ts, 7, 10))
+>toFixed : Symbol(Number.toFixed, Decl(lib.es5.d.ts, --, --))
+}
+
+type Shape =
+>Shape : Symbol(Shape, Decl(iterableWithNeverAsUnionMember.ts, 9, 1))
+
+  | { kind: "circle"; radius: number }
+>kind : Symbol(kind, Decl(iterableWithNeverAsUnionMember.ts, 12, 5))
+>radius : Symbol(radius, Decl(iterableWithNeverAsUnionMember.ts, 12, 21))
+
+  | { kind: "rectangle"; width: number; height: number };
+>kind : Symbol(kind, Decl(iterableWithNeverAsUnionMember.ts, 13, 5))
+>width : Symbol(width, Decl(iterableWithNeverAsUnionMember.ts, 13, 24))
+>height : Symbol(height, Decl(iterableWithNeverAsUnionMember.ts, 13, 39))
+
+type Circle = Shape & { kind: "circle" };
+>Circle : Symbol(Circle, Decl(iterableWithNeverAsUnionMember.ts, 13, 57))
+>Shape : Symbol(Shape, Decl(iterableWithNeverAsUnionMember.ts, 9, 1))
+>kind : Symbol(kind, Decl(iterableWithNeverAsUnionMember.ts, 15, 23))
+
+function doStuffWithCircle(arg: Circle | [Circle, (newValue: Circle) => void]) {
+>doStuffWithCircle : Symbol(doStuffWithCircle, Decl(iterableWithNeverAsUnionMember.ts, 15, 41))
+>arg : Symbol(arg, Decl(iterableWithNeverAsUnionMember.ts, 17, 27))
+>Circle : Symbol(Circle, Decl(iterableWithNeverAsUnionMember.ts, 13, 57))
+>Circle : Symbol(Circle, Decl(iterableWithNeverAsUnionMember.ts, 13, 57))
+>newValue : Symbol(newValue, Decl(iterableWithNeverAsUnionMember.ts, 17, 51))
+>Circle : Symbol(Circle, Decl(iterableWithNeverAsUnionMember.ts, 13, 57))
+
+  if (Array.isArray(arg)) {
+>Array.isArray : Symbol(ArrayConstructor.isArray, Decl(lib.es5.d.ts, --, --))
+>Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --))
+>isArray : Symbol(ArrayConstructor.isArray, Decl(lib.es5.d.ts, --, --))
+>arg : Symbol(arg, Decl(iterableWithNeverAsUnionMember.ts, 17, 27))
+
+    let [value, setValue] = arg; // ok
+>value : Symbol(value, Decl(iterableWithNeverAsUnionMember.ts, 19, 9))
+>setValue : Symbol(setValue, Decl(iterableWithNeverAsUnionMember.ts, 19, 15))
+>arg : Symbol(arg, Decl(iterableWithNeverAsUnionMember.ts, 17, 27))
+  }
+}
+
+function f1<T extends { a: "foo" } & { a: "bar" }>(x: T) {
+>f1 : Symbol(f1, Decl(iterableWithNeverAsUnionMember.ts, 21, 1))
+>T : Symbol(T, Decl(iterableWithNeverAsUnionMember.ts, 23, 12))
+>a : Symbol(a, Decl(iterableWithNeverAsUnionMember.ts, 23, 23))
+>a : Symbol(a, Decl(iterableWithNeverAsUnionMember.ts, 23, 38))
+>x : Symbol(x, Decl(iterableWithNeverAsUnionMember.ts, 23, 51))
+>T : Symbol(T, Decl(iterableWithNeverAsUnionMember.ts, 23, 12))
+
+  let [y] = x; // error
+>y : Symbol(y, Decl(iterableWithNeverAsUnionMember.ts, 24, 7))
+>x : Symbol(x, Decl(iterableWithNeverAsUnionMember.ts, 23, 51))
+}
+
+declare const o2: ({ a: "foo" } & { a: "bar" }) | ({ b: "qwe" } & { b: "rty" });
+>o2 : Symbol(o2, Decl(iterableWithNeverAsUnionMember.ts, 27, 13))
+>a : Symbol(a, Decl(iterableWithNeverAsUnionMember.ts, 27, 20))
+>a : Symbol(a, Decl(iterableWithNeverAsUnionMember.ts, 27, 35))
+>b : Symbol(b, Decl(iterableWithNeverAsUnionMember.ts, 27, 52))
+>b : Symbol(b, Decl(iterableWithNeverAsUnionMember.ts, 27, 67))
+
+const [el3] = o2; // error
+>el3 : Symbol(el3, Decl(iterableWithNeverAsUnionMember.ts, 28, 7))
+>o2 : Symbol(o2, Decl(iterableWithNeverAsUnionMember.ts, 27, 13))
+

tests/baselines/reference/iterableWithNeverAsUnionMember(target=es5).types

@@ -0,0 +1,138 @@
+//// [tests/cases/compiler/iterableWithNeverAsUnionMember.ts] ////
+
+=== iterableWithNeverAsUnionMember.ts ===
+declare const o1: { a: "foo" } & { a: "bar" };
+>o1 : never
+>   : ^^^^^
+>a : "foo"
+>  : ^^^^^
+>a : "bar"
+>  : ^^^^^
+
+const [el1] = o1; // error
+>el1 : never
+>    : ^^^^^
+>o1 : never
+>   : ^^^^^
+
+// https://github.com/microsoft/TypeScript/issues/62462
+declare var x: number[] | ({ t: "a" } & { t: "b" });
+>x : number[]
+>  : ^^^^^^^^
+>t : "a"
+>  : ^^^
+>t : "b"
+>  : ^^^
+
+let [el2] = x; // ok
+>el2 : number
+>    : ^^^^^^
+>x : number[]
+>  : ^^^^^^^^
+
+for (const elem of x) { // ok
+>elem : number
+>     : ^^^^^^
+>x : number[]
+>  : ^^^^^^^^
+
+  elem.toFixed();
+>elem.toFixed() : string
+>               : ^^^^^^
+>elem.toFixed : (fractionDigits?: number) => string
+>             : ^              ^^^      ^^^^^      
+>elem : number
+>     : ^^^^^^
+>toFixed : (fractionDigits?: number) => string
+>        : ^              ^^^      ^^^^^      
+}
+
+type Shape =
+>Shape : Shape
+>      : ^^^^^
+
+  | { kind: "circle"; radius: number }
+>kind : "circle"
+>     : ^^^^^^^^
+>radius : number
+>       : ^^^^^^
+
+  | { kind: "rectangle"; width: number; height: number };
+>kind : "rectangle"
+>     : ^^^^^^^^^^^
+>width : number
+>      : ^^^^^^
+>height : number
+>       : ^^^^^^
+
+type Circle = Shape & { kind: "circle" };
+>Circle : { kind: "circle"; radius: number; } & { kind: "circle"; }
+>       : ^^^^^^^^        ^^^^^^^^^^      ^^^^^^^^^^^^^^        ^^^
+>kind : "circle"
+>     : ^^^^^^^^
+
+function doStuffWithCircle(arg: Circle | [Circle, (newValue: Circle) => void]) {
+>doStuffWithCircle : (arg: Circle | [Circle, (newValue: Circle) => void]) => void
+>                  : ^   ^^                                             ^^^^^^^^^
+>arg : ({ kind: "circle"; radius: number; } & { kind: "circle"; }) | [{ kind: "circle"; radius: number; } & { kind: "circle"; }, (newValue: Circle) => void]
+>    : ^^^^^^^^^        ^^^^^^^^^^      ^^^^^^^^^^^^^^        ^^^^^^^^^^^^^^^^        ^^^^^^^^^^      ^^^^^^^^^^^^^^        ^^^^^^        ^^      ^^^^^    ^
+>newValue : { kind: "circle"; radius: number; } & { kind: "circle"; }
+>         : ^^^^^^^^        ^^^^^^^^^^      ^^^^^^^^^^^^^^        ^^^
+
+  if (Array.isArray(arg)) {
+>Array.isArray(arg) : boolean
+>                   : ^^^^^^^
+>Array.isArray : (arg: any) => arg is any[]
+>              : ^   ^^   ^^^^^            
+>Array : ArrayConstructor
+>      : ^^^^^^^^^^^^^^^^
+>isArray : (arg: any) => arg is any[]
+>        : ^   ^^   ^^^^^            
+>arg : ({ kind: "circle"; radius: number; } & { kind: "circle"; }) | [{ kind: "circle"; radius: number; } & { kind: "circle"; }, (newValue: Circle) => void]
+>    : ^^^^^^^^^        ^^^^^^^^^^      ^^^^^^^^^^^^^^        ^^^^^^^^^^^^^^^^        ^^^^^^^^^^      ^^^^^^^^^^^^^^        ^^^^^^        ^^      ^^^^^    ^
+
+    let [value, setValue] = arg; // ok
+>value : { kind: "circle"; radius: number; } & { kind: "circle"; }
+>      : ^^^^^^^^        ^^^^^^^^^^      ^^^^^^^^^^^^^^        ^^^
+>setValue : (newValue: Circle) => void
+>         : ^        ^^      ^^^^^    
+>arg : [{ kind: "circle"; radius: number; } & { kind: "circle"; }, (newValue: Circle) => void]
+>    : ^^^^^^^^^        ^^^^^^^^^^      ^^^^^^^^^^^^^^        ^^^^^^        ^^      ^^^^^    ^
+  }
+}
+
+function f1<T extends { a: "foo" } & { a: "bar" }>(x: T) {
+>f1 : <T extends { a: "foo"; } & { a: "bar"; }>(x: T) => void
+>   : ^ ^^^^^^^^^                             ^^ ^^ ^^^^^^^^^
+>a : "foo"
+>  : ^^^^^
+>a : "bar"
+>  : ^^^^^
+>x : T
+>  : ^
+
+  let [y] = x; // error
+>y : never
+>  : ^^^^^
+>x : T
+>  : ^
+}
+
+declare const o2: ({ a: "foo" } & { a: "bar" }) | ({ b: "qwe" } & { b: "rty" });
+>o2 : never
+>   : ^^^^^
+>a : "foo"
+>  : ^^^^^
+>a : "bar"
+>  : ^^^^^
+>b : "qwe"
+>  : ^^^^^
+>b : "rty"
+>  : ^^^^^
+
+const [el3] = o2; // error
+>el3 : never
+>    : ^^^^^
+>o2 : never
+>   : ^^^^^
+

tests/baselines/reference/iterableWithNeverAsUnionMember(target=esnext).errors.txt

@@ -0,0 +1,41 @@
+iterableWithNeverAsUnionMember.ts(2,7): error TS2488: Type 'never' must have a '[Symbol.iterator]()' method that returns an iterator.
+iterableWithNeverAsUnionMember.ts(25,7): error TS2488: Type 'T' must have a '[Symbol.iterator]()' method that returns an iterator.
+iterableWithNeverAsUnionMember.ts(29,7): error TS2488: Type 'never' must have a '[Symbol.iterator]()' method that returns an iterator.
+
+
+==== iterableWithNeverAsUnionMember.ts (3 errors) ====
+    declare const o1: { a: "foo" } & { a: "bar" };
+    const [el1] = o1; // error
+          ~~~~~
+!!! error TS2488: Type 'never' must have a '[Symbol.iterator]()' method that returns an iterator.
+
+    // https://github.com/microsoft/TypeScript/issues/62462
+    declare var x: number[] | ({ t: "a" } & { t: "b" });
+    let [el2] = x; // ok
+
+    for (const elem of x) { // ok
+      elem.toFixed();
+    }
+
+    type Shape =
+      | { kind: "circle"; radius: number }
+      | { kind: "rectangle"; width: number; height: number };
+
+    type Circle = Shape & { kind: "circle" };
+
+    function doStuffWithCircle(arg: Circle | [Circle, (newValue: Circle) => void]) {
+      if (Array.isArray(arg)) {
+        let [value, setValue] = arg; // ok
+      }
+    }
+
+    function f1<T extends { a: "foo" } & { a: "bar" }>(x: T) {
+      let [y] = x; // error
+          ~~~
+!!! error TS2488: Type 'T' must have a '[Symbol.iterator]()' method that returns an iterator.
+    }
+
+    declare const o2: ({ a: "foo" } & { a: "bar" }) | ({ b: "qwe" } & { b: "rty" });
+    const [el3] = o2; // error
+          ~~~~~
+!!! error TS2488: Type 'never' must have a '[Symbol.iterator]()' method that returns an iterator.

tests/baselines/reference/iterableWithNeverAsUnionMember(target=esnext).symbols

@@ -0,0 +1,94 @@
+//// [tests/cases/compiler/iterableWithNeverAsUnionMember.ts] ////
+
+=== iterableWithNeverAsUnionMember.ts ===
+declare const o1: { a: "foo" } & { a: "bar" };
+>o1 : Symbol(o1, Decl(iterableWithNeverAsUnionMember.ts, 0, 13))
+>a : Symbol(a, Decl(iterableWithNeverAsUnionMember.ts, 0, 19))
+>a : Symbol(a, Decl(iterableWithNeverAsUnionMember.ts, 0, 34))
+
+const [el1] = o1; // error
+>el1 : Symbol(el1, Decl(iterableWithNeverAsUnionMember.ts, 1, 7))
+>o1 : Symbol(o1, Decl(iterableWithNeverAsUnionMember.ts, 0, 13))
+
+// https://github.com/microsoft/TypeScript/issues/62462
+declare var x: number[] | ({ t: "a" } & { t: "b" });
+>x : Symbol(x, Decl(iterableWithNeverAsUnionMember.ts, 4, 11))
+>t : Symbol(t, Decl(iterableWithNeverAsUnionMember.ts, 4, 28))
+>t : Symbol(t, Decl(iterableWithNeverAsUnionMember.ts, 4, 41))
+
+let [el2] = x; // ok
+>el2 : Symbol(el2, Decl(iterableWithNeverAsUnionMember.ts, 5, 5))
+>x : Symbol(x, Decl(iterableWithNeverAsUnionMember.ts, 4, 11))
+
+for (const elem of x) { // ok
+>elem : Symbol(elem, Decl(iterableWithNeverAsUnionMember.ts, 7, 10))
+>x : Symbol(x, Decl(iterableWithNeverAsUnionMember.ts, 4, 11))
+
+  elem.toFixed();
+>elem.toFixed : Symbol(Number.toFixed, Decl(lib.es5.d.ts, --, --))
+>elem : Symbol(elem, Decl(iterableWithNeverAsUnionMember.ts, 7, 10))
+>toFixed : Symbol(Number.toFixed, Decl(lib.es5.d.ts, --, --))
+}
+
+type Shape =
+>Shape : Symbol(Shape, Decl(iterableWithNeverAsUnionMember.ts, 9, 1))
+
+  | { kind: "circle"; radius: number }
+>kind : Symbol(kind, Decl(iterableWithNeverAsUnionMember.ts, 12, 5))
+>radius : Symbol(radius, Decl(iterableWithNeverAsUnionMember.ts, 12, 21))
+
+  | { kind: "rectangle"; width: number; height: number };
+>kind : Symbol(kind, Decl(iterableWithNeverAsUnionMember.ts, 13, 5))
+>width : Symbol(width, Decl(iterableWithNeverAsUnionMember.ts, 13, 24))
+>height : Symbol(height, Decl(iterableWithNeverAsUnionMember.ts, 13, 39))
+
+type Circle = Shape & { kind: "circle" };
+>Circle : Symbol(Circle, Decl(iterableWithNeverAsUnionMember.ts, 13, 57))
+>Shape : Symbol(Shape, Decl(iterableWithNeverAsUnionMember.ts, 9, 1))
+>kind : Symbol(kind, Decl(iterableWithNeverAsUnionMember.ts, 15, 23))
+
+function doStuffWithCircle(arg: Circle | [Circle, (newValue: Circle) => void]) {
+>doStuffWithCircle : Symbol(doStuffWithCircle, Decl(iterableWithNeverAsUnionMember.ts, 15, 41))
+>arg : Symbol(arg, Decl(iterableWithNeverAsUnionMember.ts, 17, 27))
+>Circle : Symbol(Circle, Decl(iterableWithNeverAsUnionMember.ts, 13, 57))
+>Circle : Symbol(Circle, Decl(iterableWithNeverAsUnionMember.ts, 13, 57))
+>newValue : Symbol(newValue, Decl(iterableWithNeverAsUnionMember.ts, 17, 51))
+>Circle : Symbol(Circle, Decl(iterableWithNeverAsUnionMember.ts, 13, 57))
+
+  if (Array.isArray(arg)) {
+>Array.isArray : Symbol(ArrayConstructor.isArray, Decl(lib.es5.d.ts, --, --))
+>Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --) ... and 4 more)
+>isArray : Symbol(ArrayConstructor.isArray, Decl(lib.es5.d.ts, --, --))
+>arg : Symbol(arg, Decl(iterableWithNeverAsUnionMember.ts, 17, 27))
+
+    let [value, setValue] = arg; // ok
+>value : Symbol(value, Decl(iterableWithNeverAsUnionMember.ts, 19, 9))
+>setValue : Symbol(setValue, Decl(iterableWithNeverAsUnionMember.ts, 19, 15))
+>arg : Symbol(arg, Decl(iterableWithNeverAsUnionMember.ts, 17, 27))
+  }
+}
+
+function f1<T extends { a: "foo" } & { a: "bar" }>(x: T) {
+>f1 : Symbol(f1, Decl(iterableWithNeverAsUnionMember.ts, 21, 1))
+>T : Symbol(T, Decl(iterableWithNeverAsUnionMember.ts, 23, 12))
+>a : Symbol(a, Decl(iterableWithNeverAsUnionMember.ts, 23, 23))
+>a : Symbol(a, Decl(iterableWithNeverAsUnionMember.ts, 23, 38))
+>x : Symbol(x, Decl(iterableWithNeverAsUnionMember.ts, 23, 51))
+>T : Symbol(T, Decl(iterableWithNeverAsUnionMember.ts, 23, 12))
+
+  let [y] = x; // error
+>y : Symbol(y, Decl(iterableWithNeverAsUnionMember.ts, 24, 7))
+>x : Symbol(x, Decl(iterableWithNeverAsUnionMember.ts, 23, 51))
+}
+
+declare const o2: ({ a: "foo" } & { a: "bar" }) | ({ b: "qwe" } & { b: "rty" });
+>o2 : Symbol(o2, Decl(iterableWithNeverAsUnionMember.ts, 27, 13))
+>a : Symbol(a, Decl(iterableWithNeverAsUnionMember.ts, 27, 20))
+>a : Symbol(a, Decl(iterableWithNeverAsUnionMember.ts, 27, 35))
+>b : Symbol(b, Decl(iterableWithNeverAsUnionMember.ts, 27, 52))
+>b : Symbol(b, Decl(iterableWithNeverAsUnionMember.ts, 27, 67))
+
+const [el3] = o2; // error
+>el3 : Symbol(el3, Decl(iterableWithNeverAsUnionMember.ts, 28, 7))
+>o2 : Symbol(o2, Decl(iterableWithNeverAsUnionMember.ts, 27, 13))
+