Bug that kill TypeScript build time

[nisimjoseph]

🔎 Search Terms

"long time", "stuck build"

🕗 Version & Regression Information

• Occur on all versions.

⏯ Playground Link

No response

💻 Code

export type HtmlAnchorTarget = '_self' | '_blank' | '_parent' | '_top';

type CssAbsoluteUnit = 'cm' | 'mm' | 'in' | 'px' | 'pt' | 'pc';
type CssRelativeUnit = 'em' | 'ex' | 'ch' | 'rem' | 'vw' | 'vh' | 'vmin' | 'vmax' | '%';

export type CssLength = `${number}${CssAbsoluteUnit | CssRelativeUnit}`;
export type CssMargin = CssLength | `${CssLength} ${CssLength}` | `${CssLength} ${CssLength} ${CssLength} ${CssLength}`;

🙁 Actual behavior

the build time grow exponential because of the amount of permutations we have and it Stuck the IDE completely and make the TSC to take 4-5x more build time.

🙂 Expected behavior

run faster

Additional information about the issue

just change the line:

export type CssMargin = CssLength | `${CssLength} ${CssLength}` | `${CssLength} ${CssLength} ${CssLength} ${CssLength}`;

to:

export type CssMargin = CssLength | string;

and all run fast.

[RyanCavanaugh]

    `${CssLength} ${CssLength} ${CssLength} ${CssLength}`

This type is a shorthand for writing the 50,000+-member expansion of all its possible values, so its performance is the same as if you had written a 50,000-member type.

[nisimjoseph]

You are right, this is not a defect or a bug.
We discovered that today, but the issue is we didn't know about it until we tracked back in all the code for the last 2 weeks, and it lot of code.
it was good to have some kind of warning in the compile time to note there is a potential issue with X that can cause a long build time, or something like that.

[RyanCavanaugh]

There is a threshold for an error, but this sample is slightly below it

[nisimjoseph]

so the threshold is 50k and we reach to little lower. ok.
can we config this threshold? 50k is too much and pretty kill the compiler time.

[MartinJohns]

It's not configurable, and likely won't be: #44997 (comment)

[nisimjoseph]

10x for the data.