-
Notifications
You must be signed in to change notification settings - Fork 12.4k
New issue
Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.
By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.
Already on GitHub? Sign in to your account
New 'unknown' top type #24439
New 'unknown' top type #24439
Conversation
Where'd we end up with mapped conditional types w.r.t |
Does that make sense (is this derived from something else)? If |
@weswigham No, that probably doesn't make sense. We should be similar to |
@RyanCavanaugh Do you mean the behavior of |
@@ -19624,7 +19644,7 @@ namespace ts { | |||
} | |||
|
|||
// Functions with with an explicitly specified 'void' or 'any' return type don't need any return expressions. | |||
if (returnType && maybeTypeOfKind(returnType, TypeFlags.Any | TypeFlags.Void)) { | |||
if (returnType && maybeTypeOfKind(returnType, TypeFlags.AnyOrUnknown | TypeFlags.Void)) { |
There was a problem hiding this comment.
Choose a reason for hiding this comment
The reason will be displayed to describe this comment to others. Learn more.
I think a function returning an explicit unknown
should probably have return values? Otherwise you should've written void
or undefined
, right?
There was a problem hiding this comment.
Choose a reason for hiding this comment
The reason will be displayed to describe this comment to others. Learn more.
Not sure about that. undefined
is in the domain of unknown
(just like it is in the domain of any
) and that's really what should guide us here.
There was a problem hiding this comment.
Choose a reason for hiding this comment
The reason will be displayed to describe this comment to others. Learn more.
Hm. Fair. Do we handle unions with undefined
in accordance with that, then?
There was a problem hiding this comment.
Choose a reason for hiding this comment
The reason will be displayed to describe this comment to others. Learn more.
We do, but with a few wrinkles. If the return type annotation includes void
, any
, or unknown
we don't require any return
statements. Otherwise, if the return type includes undefined
we require at least one return
statement somewhere, but don't require return
statements to have expressions and allow the end point of the function to be reachable. Otherwise, we require a return
statement with an expression at every exit point.
@@ -403,7 +403,7 @@ interface B1<T> extends A1<T> { | |||
>T : T | |||
|
|||
boom: T extends any ? true : true | |||
>boom : T extends any ? true : true |
There was a problem hiding this comment.
Choose a reason for hiding this comment
The reason will be displayed to describe this comment to others. Learn more.
why did this type collapse to true
?
There was a problem hiding this comment.
Choose a reason for hiding this comment
The reason will be displayed to describe this comment to others. Learn more.
I changed this to eagerly resolve to true
when the extends type is any
or unknown
(since it always will be).
There was a problem hiding this comment.
Choose a reason for hiding this comment
The reason will be displayed to describe this comment to others. Learn more.
Ah, but what about T extends any ? { x: T } : never
- that needs to distribute.
There was a problem hiding this comment.
Choose a reason for hiding this comment
The reason will be displayed to describe this comment to others. Learn more.
Hmm, yes, I suppose we can only optimize when the conditional type isn't distributive.
There was a problem hiding this comment.
Choose a reason for hiding this comment
The reason will be displayed to describe this comment to others. Learn more.
There's a better check (than just distributivity) that I have an outstanding PR for: instantiate the check type (and infer types) in the true/false types with wildcards. If the instantiation isn't the input type, you can't simplify. If it is, you can. (Since the type isn't affected by instantiation)
The BaseController state now uses `unknown` rather than `any` as the type for state properties. `unknown` is more type-safe than `any` in cases like this where we don't know what type to expect. See here for details [1]. This was suggested by @rekmarks during review of #362 [2]. [1]: microsoft/TypeScript#24439 [2]: #362 (comment)
* Use `unknown` rather than `any` for BaseController state The BaseController state now uses `unknown` rather than `any` as the type for state properties. `unknown` is more type-safe than `any` in cases like this where we don't know what type to expect. See here for details [1]. This was suggested by @rekmarks during review of #362 [2]. [1]: microsoft/TypeScript#24439 [2]: #362 (comment) * Use type alias for controller state rather than interface The mock controller state in the base controller tests now uses a type alias for the controller state rather than an interface. This was required to get around an incompatibility between `Record<string, unknown>` and interfaces[1]. The `@typescript-eslint/consistent-type-definitions` ESLint rule has been disabled, as this problem will be encountered fairly frequently. [1]: microsoft/TypeScript#15300 (comment)
* Use `unknown` rather than `any` for BaseController state The BaseController state now uses `unknown` rather than `any` as the type for state properties. `unknown` is more type-safe than `any` in cases like this where we don't know what type to expect. See here for details [1]. This was suggested by @rekmarks during review of #362 [2]. [1]: microsoft/TypeScript#24439 [2]: #362 (comment) * Use type alias for controller state rather than interface The mock controller state in the base controller tests now uses a type alias for the controller state rather than an interface. This was required to get around an incompatibility between `Record<string, unknown>` and interfaces[1]. The `@typescript-eslint/consistent-type-definitions` ESLint rule has been disabled, as this problem will be encountered fairly frequently. [1]: microsoft/TypeScript#15300 (comment)
* Use `unknown` rather than `any` for BaseController state The BaseController state now uses `unknown` rather than `any` as the type for state properties. `unknown` is more type-safe than `any` in cases like this where we don't know what type to expect. See here for details [1]. This was suggested by @rekmarks during review of #362 [2]. [1]: microsoft/TypeScript#24439 [2]: #362 (comment) * Use type alias for controller state rather than interface The mock controller state in the base controller tests now uses a type alias for the controller state rather than an interface. This was required to get around an incompatibility between `Record<string, unknown>` and interfaces[1]. The `@typescript-eslint/consistent-type-definitions` ESLint rule has been disabled, as this problem will be encountered fairly frequently. [1]: microsoft/TypeScript#15300 (comment)
This PR adds a new top type
unknown
which is the type-safe counterpart ofany
. Anything is assignable tounknown
, butunknown
isn't assignable to anything but itself andany
without a type assertion or a control flow based narrowing. Likewise, no operations are permitted on anunknown
without first asserting or narrowing to a more specific type.Note that this PR is technically a breaking change since
unknown
becomes a reserved type name.Fixes #10715.