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Array(n).fill(value) isn't typechecked #7887

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julienw opened this issue Jul 4, 2019 · 5 comments · May be fixed by #7917
Open

Array(n).fill(value) isn't typechecked #7887

julienw opened this issue Jul 4, 2019 · 5 comments · May be fixed by #7917
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bug Has PR Library definitions Issues or pull requests about core library definitions Typing: soundness No false negatives (type checker claims that there is no error in the incorrect program)

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@julienw
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julienw commented Jul 4, 2019

With this code, Flow doesn't find the error:

type Plop = {
  prop: string[],
};

var a: Plop = {
  prop: Array(5).fill(1),
}

I believe this is because the Array constructor returns an array of any items in

flow/lib/core.js

Line 293 in f796b60

static (...values:Array<any>): Array<any>;
.

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@julienw
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julienw commented Jul 4, 2019

Interestingly it works fine with new Array :)

@canova
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canova commented Jul 4, 2019

ECMA says Array function is the same with the array constructor. I don't know the codebase but probably we are missing that function or there is something with its type.
See the spec (section 15.4.1, The Array Constructor Called as a Function)

@goodmind
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goodmind commented Jul 4, 2019

Array constructor is defined in OCaml code for some reason

@goodmind
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goodmind commented Jul 4, 2019

flow/src/typing/statement.ml

Lines 3068 to 3115 in f796b60

| New {
New.callee = callee_loc, Identifier (id_loc, ({ Ast.Identifier.name= "Array" as n; comments= _ } as name));
targs;
arguments
} -> (
let targts = Option.map targs (fun (loc, args) ->
loc, (convert_tparam_instantiations cx SMap.empty args)
) in
let args = Core_list.map ~f:(expression_or_spread cx) arguments in
let result = match targts, args with
| Some (loc, ([t], [elem_t])), [Arg argt, arg] -> Ok (Some (loc, elem_t, t), argt, arg)
| None, [Arg argt, arg] -> Ok (None, argt, arg)
| None, _ -> Error (Error_message.EUseArrayLiteral loc)
| Some _, _ ->
Error Error_message.(ECallTypeArity {
call_loc = loc;
is_new = true;
reason_arity = Reason.(locationless_reason (RType n));
expected_arity = 1;
})
in
match result with
| Ok (targ_t, arg_t, arg) ->
let reason = mk_reason (RCustom "new Array(..)") loc in
let length_reason =
replace_reason_const (RCustom "array length") reason in
Flow.flow_t cx (arg_t, DefT (length_reason, bogus_trust (), NumT AnyLiteral));
let t, targs = match targ_t with
| Some (loc, ast, ExplicitArg t) -> t, Some (loc, [ast])
| Some (_, _, ImplicitArg _)
| None ->
let element_reason =
replace_reason_const (RCustom "array element") reason in
Tvar.mk cx element_reason, None
in
let id_t = identifier cx name callee_loc in
(* TODO - tuple_types could be undefined x N if given a literal *)
(loc, DefT (reason, bogus_trust (), ArrT (ArrayAT (t, None)))),
New { New.
callee = (callee_loc, id_t), Identifier ((id_loc, id_t), name);
targs;
arguments = [arg];
}
| Error err ->
Flow.add_output cx err;
Tast_utils.error_mapper#expression ex
)

@goodmind
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goodmind commented Jul 4, 2019 •
edited
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Not sure why it's not possible to typecheck it like this instead of doing this kind of hardcoding
https://flow.org/try/#0CYUwxgNghgTiAEkoGdnwLIE8CCMZUwB4AVAPngG8AoeRAewDtkAXGAVzGbpgAoGAueAzYBbAEYgYASkG58RECIAOzTKQDcNek1YcuvAHRHYAc2SDiAbQC6M+HIIkNWrSyjMAlmHh9Bw8ZJ2DgrKqs60bp7ePEYGpubwVrayeI5kmgC+LmCMLPAAZnR08AC8GDipmDwArFJUOTrwYrCl5cE8AIwANPAATD0AzHX1ucwFRQAMrQwgAO5tlTV1DXnNMFNlM-NY7d19g1JAA
this error just doesn't make sense

13: const bar0 = new Array(1, 2, 3)                 
^ Use an array literal instead of `new Array(...)`.

@mvitousek mvitousek added Typing: soundness No false negatives (type checker claims that there is no error in the incorrect program) and removed needs triage labels Jul 4, 2019
@goodmind goodmind linked a pull request Jul 10, 2019 that will close this issue
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@SamChou19815 SamChou19815 added the Library definitions Issues or pull requests about core library definitions label Aug 8, 2023
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Better signature for callable array goodmind/flow
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@julienw @canova @mvitousek @goodmind @SamChou19815