fix: Typescript type fixes for themes and types functions

[nmn]

What changed / motivation ?

Made some changes to the Flow types so that the generated Typescript types are valid.

Also made some changes to a typescript .d.ts file to make it valid.

Linked PR/Issues

Fixes #969

Additional Context

Some type constraints loosened up so various stylex.types.* classes would have the same constraints to make things work correctly in Typescript.

This doesn't actually make the types less strict because the type constraints on the actual functions are unchanged.

[github-actions[bot]]

workflow: benchmarks/perf

Comparison of performance test results, measured in operations per second. Larger is better.

[email protected] compare node ./compare.js /tmp/tmp.JjlVgwCDX0 /tmp/tmp.jh29Uk4po7

Results	Base	Patch	Ratio
babel-plugin: stylex.create
· basic create	519	516	0.99	-
· complex create	186	182	0.98	-
babel-plugin: stylex.createTheme
· basic themes	445	448	1.01	+
· complex themes	41	41	1.00

[github-actions[bot]]

workflow: benchmarks/size

Comparison of minified (terser) and compressed (brotli) size results, measured in bytes. Smaller is better.

[email protected] compare node ./compare.js /tmp/tmp.UlZUofh8C7 /tmp/tmp.KnPudfhZjf

Results	Base	Patch	Ratio
@stylexjs/stylex/lib/cjs/stylex.js
· compressed	1,200	1,200	1.00
· minified	3,513	3,513	1.00
@stylexjs/stylex/lib/cjs/inject.js
· compressed	1,227	1,227	1.00
· minified	3,224	3,224	1.00
benchmarks/size/.build/bundle.js
· compressed	537,611	537,611	1.00
· minified	7,435,904	7,435,904	1.00
benchmarks/size/.build/stylex.css
· compressed	100,509	100,509	1.00
· minified	754,513	754,513	1.00

[AlexanderOMara]

Looks good to me.

[AlexanderOMara]

Oh, one other new issue compared to the current release. Looks like StyleX$DefineConsts is missing in StyleXTypes.d.ts (out-of-sync since it was added to StyleXTypes.js), it has the same type as StyleX$DefineVars and easy to add:

export type StyleX$DefineVars = <
  DefaultTokens extends TTokens,
  ID extends symbol = symbol,
>(
  tokens: DefaultTokens,
) => VarGroup<FlattenTokens<DefaultTokens>, ID>;

export type StyleX$DefineConsts = <
  DefaultTokens extends TTokens,
  ID extends symbol = symbol,
>(
  tokens: DefaultTokens,
) => VarGroup<FlattenTokens<DefaultTokens>, ID>;

With StyleX$DefineConsts added this branch produces types that are strictly valid!

[necolas]

StyleXTypes.d.ts (out-of-sync since it was added to StyleXTypes.js),

Can we avoid having a manual StyleXTypes.d.ts file and generate that too?

[AlexanderOMara]

That would probably be better to avoid inconsistencies, looks like there might be some other inconsistencies.

Seeing these errors when StyleXTypes.d.ts is generated with the code in this branch:

$ tsc

.../stylex/lib/StyleXTypes.d.ts:89:24 - error TS2411: Property 'default' of type 'A' is not assignable to 'string' index type 'B'.

89               readonly default: infer A;
                          ~~~~~~~

.../stylex/lib/StyleXTypes.d.ts:106:51 - error TS2344: Type 'Obj' does not satisfy the constraint '{ readonly [$$Key$$: string]: unknown; }'.

106       ? (...args: Args) => Readonly<[MapNamespace<Obj>, InlineStyles]>
                                                      ~~~

  .../stylex/lib/StyleXTypes.d.ts:105:69
    105     [Key in keyof S]: S[Key] extends (...args: infer Args) => infer Obj
                                                                            ~~~
    This type parameter might need an `extends { readonly [$$Key$$: string]: unknown; }` constraint.

.../stylex/lib/StyleXTypes.d.ts:107:22 - error TS2344: Type 'S[Key]' does not satisfy the constraint '{ readonly [$$Key$$: string]: unknown; }'.
  Type 'S[keyof S]' is not assignable to type '{ readonly [$$Key$$: string]: unknown; }'.
    Type 'S[string] | S[number] | S[symbol]' is not assignable to type '{ readonly [$$Key$$: string]: unknown; }'.
      Type 'S[string]' is not assignable to type '{ readonly [$$Key$$: string]: unknown; }'.

107       : MapNamespace<S[Key]>;
                         ~~~~~~

.../stylex/lib/StyleXTypes.d.ts:113:3 - error TS2411: Property '$$css' of type 'true' is not assignable to 'string' index type 'string'.

113   $$css: true;
      ~~~~~

.../stylex/lib/StyleXTypes.d.ts:116:39 - error TS2411: Property '$$css' of type 'void | undefined' is not assignable to 'string' index type 'string'.

116 export type InlineStyles = Readonly<{ $$css?: void; [key: string]: string }>;
                                          ~~~~~

.../stylex/lib/StyleXTypes.d.ts:177:20 - error TS2411: Property 'default' of type 'X' is not assignable to 'string' index type 'Y'.

177           readonly default: infer X;
                       ~~~~~~~


Found 6 errors in the same file, starting at: .../stylex/lib/StyleXTypes.d.ts:89