Try not allowing string iteration

src/lib/es2015.iterable.d.ts

@@ -249,7 +249,7 @@ interface StringIterator<T> extends IteratorObject<T, BuiltinIteratorReturn, unk
 
 interface String {
     /** Iterator */
-    [Symbol.iterator](): StringIterator<string>;
+    // [Symbol.iterator](): StringIterator<string>;
 }
 
 interface Int8Array {

tests/baselines/reference/ES5For-ofTypeCheck14.errors.txt

@@ -1,8 +1,8 @@
-ES5For-ofTypeCheck14.ts(2,17): error TS2802: Type 'Set<number>' can only be iterated through when using the '--downlevelIteration' flag or with a '--target' of 'es2015' or higher.
+ES5For-ofTypeCheck14.ts(2,17): error TS2461: Type 'Set<number>' is not an array type.
 
 
 ==== ES5For-ofTypeCheck14.ts (1 errors) ====
     var union: string | Set<number>
     for (const e of union) { }
                     ~~~~~
-!!! error TS2802: Type 'Set<number>' can only be iterated through when using the '--downlevelIteration' flag or with a '--target' of 'es2015' or higher.
+!!! error TS2461: Type 'Set<number>' is not an array type.

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

@@ -0,0 +1,34 @@
+argumentsSpreadRestIterables.tsx(8,21): error TS2488: Type '"hello"' must have a '[Symbol.iterator]()' method that returns an iterator.
+argumentsSpreadRestIterables.tsx(10,27): error TS2488: Type '"hello"' must have a '[Symbol.iterator]()' method that returns an iterator.
+argumentsSpreadRestIterables.tsx(15,19): error TS2488: Type '"hello"' must have a '[Symbol.iterator]()' method that returns an iterator.
+argumentsSpreadRestIterables.tsx(17,25): error TS2488: Type '"hello"' must have a '[Symbol.iterator]()' method that returns an iterator.
+
+
+==== argumentsSpreadRestIterables.tsx (4 errors) ====
+    declare const itNum: Iterable<number>
+
+    ;(function(...rest) {})(...itNum)
+    ;(function(a, ...rest) {})('', ...itNum)
+    ;(function(a, ...rest) {})('', true, ...itNum)
+
+    declare function fn1<const T extends readonly unknown[]>(...args: T): T;
+    const res1 = fn1(..."hello");
+                        ~~~~~~~
+!!! error TS2488: Type '"hello"' must have a '[Symbol.iterator]()' method that returns an iterator.
+    const res2 = fn1(...itNum);
+    const res3 = fn1(true, ..."hello");
+                              ~~~~~~~
+!!! error TS2488: Type '"hello"' must have a '[Symbol.iterator]()' method that returns an iterator.
+    const res4 = fn1(true, ...itNum);
+
+    // repro from #52781
+    declare function foo<T extends unknown[]>(...args: T): T;
+    const p1 = foo(..."hello");
+                      ~~~~~~~
+!!! error TS2488: Type '"hello"' must have a '[Symbol.iterator]()' method that returns an iterator.
+    const p2 = foo(...itNum);
+    const p3 = foo(true, ..."hello");
+                            ~~~~~~~
+!!! error TS2488: Type '"hello"' must have a '[Symbol.iterator]()' method that returns an iterator.
+    const p4 = foo(true, ...itNum);
+

tests/baselines/reference/argumentsSpreadRestIterables(target=esnext).types

@@ -64,14 +64,14 @@ declare function fn1<const T extends readonly unknown[]>(...args: T): T;
 >     : ^
 
 const res1 = fn1(..."hello");
->res1 : readonly string[]
->     : ^^^^^^^^^^^^^^^^^
->fn1(..."hello") : readonly string[]
->                : ^^^^^^^^^^^^^^^^^
+>res1 : readonly any[]
+>     : ^^^^^^^^^^^^^^
+>fn1(..."hello") : readonly any[]
+>                : ^^^^^^^^^^^^^^
 >fn1 : <const T extends readonly unknown[]>(...args: T) => T
 >    : ^^^^^^^ ^^^^^^^^^                  ^^^^^    ^^ ^^^^^ 
->..."hello" : string
->           : ^^^^^^
+>..."hello" : any
+>           : ^^^
 >"hello" : "hello"
 >        : ^^^^^^^
 
@@ -88,16 +88,16 @@ const res2 = fn1(...itNum);
 >      : ^^^^^^^^^^^^^^^^
 
 const res3 = fn1(true, ..."hello");
->res3 : readonly [true, ...string[]]
->     : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
->fn1(true, ..."hello") : readonly [true, ...string[]]
->                      : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+>res3 : readonly [true, ...any[]]
+>     : ^^^^^^^^^^^^^^^^^^^^^^^^^
+>fn1(true, ..."hello") : readonly [true, ...any[]]
+>                      : ^^^^^^^^^^^^^^^^^^^^^^^^^
 >fn1 : <const T extends readonly unknown[]>(...args: T) => T
 >    : ^^^^^^^ ^^^^^^^^^                  ^^^^^    ^^ ^^^^^ 
 >true : true
 >     : ^^^^
->..."hello" : string
->           : ^^^^^^
+>..."hello" : any
+>           : ^^^
 >"hello" : "hello"
 >        : ^^^^^^^
 
@@ -123,14 +123,14 @@ declare function foo<T extends unknown[]>(...args: T): T;
 >     : ^
 
 const p1 = foo(..."hello");
->p1 : string[]
->   : ^^^^^^^^
->foo(..."hello") : string[]
->                : ^^^^^^^^
+>p1 : any[]
+>   : ^^^^^
+>foo(..."hello") : any[]
+>                : ^^^^^
 >foo : <T extends unknown[]>(...args: T) => T
 >    : ^ ^^^^^^^^^         ^^^^^    ^^ ^^^^^ 
->..."hello" : string
->           : ^^^^^^
+>..."hello" : any
+>           : ^^^
 >"hello" : "hello"
 >        : ^^^^^^^
 
@@ -147,16 +147,16 @@ const p2 = foo(...itNum);
 >      : ^^^^^^^^^^^^^^^^
 
 const p3 = foo(true, ..."hello");
->p3 : [boolean, ...string[]]
->   : ^^^^^^^^^^^^^^^^^^^^^^
->foo(true, ..."hello") : [boolean, ...string[]]
->                      : ^^^^^^^^^^^^^^^^^^^^^^
+>p3 : [boolean, ...any[]]
+>   : ^^^^^^^^^^^^^^^^^^^
+>foo(true, ..."hello") : [boolean, ...any[]]
+>                      : ^^^^^^^^^^^^^^^^^^^
 >foo : <T extends unknown[]>(...args: T) => T
 >    : ^ ^^^^^^^^^         ^^^^^    ^^ ^^^^^ 
 >true : true
 >     : ^^^^
->..."hello" : string
->           : ^^^^^^
+>..."hello" : any
+>           : ^^^
 >"hello" : "hello"
 >        : ^^^^^^^
 

tests/baselines/reference/for-of9.errors.txt

@@ -0,0 +1,9 @@
+for-of9.ts(3,11): error TS2488: Type '"hello"' must have a '[Symbol.iterator]()' method that returns an iterator.
+
+
+==== for-of9.ts (1 errors) ====
+    var v: string;
+    for (v of ["hello"]) { }
+    for (v of "hello") { }
+              ~~~~~~~
+!!! error TS2488: Type '"hello"' must have a '[Symbol.iterator]()' method that returns an iterator.

tests/baselines/reference/iterableArrayPattern8.types

@@ -73,8 +73,8 @@ var a: Bar, b: string;
 >          : ^^^^^^^^^^^^^^^^^^
 >a : Bar
 >  : ^^^
->...b : string
->     : ^^^^^^
+>...b : any
+>     : ^^^
 >b : string
 >  : ^^^^^^
 >new FooIterator : FooIterator

tests/baselines/reference/mapGroupBy.errors.txt

@@ -0,0 +1,16 @@
+mapGroupBy.ts(3,27): error TS2345: Argument of type 'string' is not assignable to parameter of type 'Iterable<unknown>'.
+
+
+==== mapGroupBy.ts (1 errors) ====
+    const basic = Map.groupBy([0, 2, 8], x => x < 5 ? 'small' : 'large');
+
+    const chars = Map.groupBy('a string', c => c);
+                              ~~~~~~~~~~
+!!! error TS2345: Argument of type 'string' is not assignable to parameter of type 'Iterable<unknown>'.
+
+    type Employee = { name: string, role: 'ic' | 'manager' }
+    const employees: Set<Employee> = new Set();
+    const byRole = Map.groupBy(employees, x => x.role);
+
+    const byNonKey = Map.groupBy(employees, x => x);
+

tests/baselines/reference/mapGroupBy.types

@@ -42,10 +42,10 @@ const basic = Map.groupBy([0, 2, 8], x => x < 5 ? 'small' : 'large');
 >        : ^^^^^^^
 
 const chars = Map.groupBy('a string', c => c);
->chars : Map<string, string[]>
->      : ^^^^^^^^^^^^^^^^^^^^^
->Map.groupBy('a string', c => c) : Map<string, string[]>
->                                : ^^^^^^^^^^^^^^^^^^^^^
+>chars : Map<unknown, unknown[]>
+>      : ^^^^^^^^^^^^^^^^^^^^^^^
+>Map.groupBy('a string', c => c) : Map<unknown, unknown[]>
+>                                : ^^^^^^^^^^^^^^^^^^^^^^^
 >Map.groupBy : <K, T>(items: Iterable<T>, keySelector: (item: T, index: number) => K) => Map<K, T[]>
 >            : ^ ^^ ^^     ^^           ^^           ^^                             ^^^^^           
 >Map : MapConstructor
@@ -54,12 +54,12 @@ const chars = Map.groupBy('a string', c => c);
 >        : ^ ^^ ^^     ^^           ^^           ^^                             ^^^^^           
 >'a string' : "a string"
 >           : ^^^^^^^^^^
->c => c : (c: string) => string
->       : ^ ^^^^^^^^^^^^^^^^^^^
->c : string
->  : ^^^^^^
->c : string
->  : ^^^^^^
+>c => c : (c: unknown) => unknown
+>       : ^ ^^^^^^^^^^^^^^^^^^^^^
+>c : unknown
+>  : ^^^^^^^
+>c : unknown
+>  : ^^^^^^^
 
 type Employee = { name: string, role: 'ic' | 'manager' }
 >Employee : Employee

tests/baselines/reference/objectGroupBy.errors.txt

@@ -1,10 +1,13 @@
+objectGroupBy.ts(3,30): error TS2345: Argument of type 'string' is not assignable to parameter of type 'Iterable<unknown>'.
 objectGroupBy.ts(9,49): error TS2322: Type 'Employee' is not assignable to type 'PropertyKey'.
 
 
-==== objectGroupBy.ts (1 errors) ====
+==== objectGroupBy.ts (2 errors) ====
     const basic = Object.groupBy([0, 2, 8], x => x < 5 ? 'small' : 'large');
 
     const chars = Object.groupBy('a string', c => c);
+                                 ~~~~~~~~~~
+!!! error TS2345: Argument of type 'string' is not assignable to parameter of type 'Iterable<unknown>'.
 
     type Employee = { name: string, role: 'ic' | 'manager' }
     const employees: Set<Employee> = new Set();

tests/baselines/reference/objectGroupBy.types

@@ -42,10 +42,10 @@ const basic = Object.groupBy([0, 2, 8], x => x < 5 ? 'small' : 'large');
 >        : ^^^^^^^
 
 const chars = Object.groupBy('a string', c => c);
->chars : Partial<Record<string, string[]>>
->      : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
->Object.groupBy('a string', c => c) : Partial<Record<string, string[]>>
->                                   : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+>chars : Partial<Record<PropertyKey, unknown[]>>
+>      : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+>Object.groupBy('a string', c => c) : Partial<Record<PropertyKey, unknown[]>>
+>                                   : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 >Object.groupBy : <K extends PropertyKey, T>(items: Iterable<T>, keySelector: (item: T, index: number) => K) => Partial<Record<K, T[]>>
 >               : ^ ^^^^^^^^^           ^^ ^^     ^^           ^^           ^^                             ^^^^^                       
 >Object : ObjectConstructor
@@ -54,12 +54,12 @@ const chars = Object.groupBy('a string', c => c);
 >        : ^ ^^^^^^^^^           ^^ ^^     ^^           ^^           ^^                             ^^^^^                       
 >'a string' : "a string"
 >           : ^^^^^^^^^^
->c => c : (c: string) => string
->       : ^ ^^^^^^^^^^^^^^^^^^^
->c : string
->  : ^^^^^^
->c : string
->  : ^^^^^^
+>c => c : (c: unknown) => unknown
+>       : ^ ^^^^^^^^^^^^^^^^^^^^^
+>c : unknown
+>  : ^^^^^^^
+>c : unknown
+>  : ^^^^^^^
 
 type Employee = { name: string, role: 'ic' | 'manager' }
 >Employee : Employee

tests/baselines/reference/typeArgumentInferenceApparentType1.errors.txt

@@ -0,0 +1,11 @@
+typeArgumentInferenceApparentType1.ts(5,26): error TS2345: Argument of type 'string' is not assignable to parameter of type 'Iterable<string>'.
+
+
+==== typeArgumentInferenceApparentType1.ts (1 errors) ====
+    function method<T>(iterable: Iterable<T>): T {
+        return;
+    }
+
+    var res: string = method("test");
+                             ~~~~~~
+!!! error TS2345: Argument of type 'string' is not assignable to parameter of type 'Iterable<string>'.