[typescript] WithStyles<typeof styles> makes theme required

• This is not a v0.x issue.
• I have searched the issues of this repository and believe that this is not a duplicate.

Expected Behavior

type Props = WithStyles<typeof styles> or WithStyles<typeof styles, undefined> should not have theme as required.

Current Behavior

type Props = WithStyles<typeof styles> has theme as required;

Steps to Reproduce

Link: https://github.com/geirsagberg/material-bug

Context

The problem appeared after upgrading to 3.1.0. Cannot seem to reproduce in Codesandbox, only locally. Clone the mentioned repo to reproduce.

Your Environment

Tech	Version
Material-UI	v3.1.0
React	v16.5.1
Browser	-
TypeScript	3.0.3
etc.

[eps1lon]

The problem here was that strictNullChecks: false worked perfectly fine in 3.0.3 and prior, and no longer worked in 3.1.0, without the release notes mentioning this at all.

It did not as my example pointed out. It only worked if you consider passing at compile time while throwing at runtime as “working”. I will file a PR that includes your fix and a bit of documentation but saying that it was working with strictNullChecks disabled is wrong. DefinitelyTyped is not documenting this as well which is an issue but documenting a requirement is (in my opinion) not a breaking change.

It’s very convenient that we can apply a fix that is compliant with both configurations but we never have supported strictNullChecks disabled and neither is DefinitelyTyped so I don’t see a reason that we should.

I can already see the issues were people complain that accessing theme at compile time is fine while it throws at runtime and that we should fix this which we can’t because some people were relying on a bug.

[eps1lon]

@dotbear I’m very sorry that this caused so many issues for you. Aside from the issue with theme it should’ve been as simple as

- export const MyComponent = decorate<Props>(props => <Button />)
+ export const MyComponent = decorate((props: Props) => <Button />)

where Props extends WithStyles.

Type definitions and semver don’t really mix very well. The definitions over at DefinitelyTyped don’t follow semver at the moment and I believe that this is ok. Mixing the definitions into the package can cause problems across minor versions. The overall problem is that the old withStyles did not support defaultProps and could’ve been considered a bug that required a breaking change. From my experience with type definitions this happens very often and would require a frequent bump in major versions which might leave non-ts users behind.

In retrospect we could’ve simply added a withStylesLibraryManaged that supported defaultProps. This would’ve allowed users to get typed defaultProps with the new method while we could still support legacy code bases with the inferior withStyles.

I would suggest using @ts-ignore if this is possible. The code will emit just fine. It’s just much noise in the form of false positives.