Extremely slow compilation; resolving generics?

[mmorearty]

TypeScript Version: 3.5.0-dev.20190405

Search Terms: slow compilation generics

Code

example.zip

Expected behavior:

Compilation should take a reasonable amount of time

Actual behavior:

On my MacBook Pro, compilation takes 31 seconds before any error messages appear.

I suspect this may have to do with the compiler trying to resolve generic types. A few comments:

• The code is hard to read, because I had to obfuscate it. Sorry about that.
• This is a hacked-up version of some of our real code. The real version compiles successfully (unlike this hacked-up one which produces errors). This is based on a TypeScript module we have that takes two minutes to compile. It only has 19,000 lines of .ts files plus 100,000 lines of .d.ts files. Most of our similar-sized modules take about 30 seconds.
• Take a look at the declaration of create at the bottom of src/sb_by_hr.ts. If you take out all the fancy generics, and instead put export const create = React.createFactory(Component);, compilation takes only 2 seconds.
• You'll notice that lib/a.d.ts has a fairly large number of type declarations. The declare module "a/dm/ps" section is about 2800 lines of one- or two-line type declarations, and declare module "a/dm/pm" is about 3800. If you delete large chunks of type declarations from either one of those blocks, the compilation times goes down. It seems to go down. For example, if you delete about half of the types from "a/dm/ps", compilation time goes from 31 seconds down to 11.8 seconds. Similarly, if you delete about half of the types from "a/dm/pm", the time goes down to 11 seconds.

Related Issues:

These may or may not be related:

• TypeScript Extremely Slow
• Super slow compilation in rare cases when mixing explicit typing, generis and type inference

[Veetaha]

I would even say more, my project compilation fails with heap overflow.

This issue is somewhat connected to #30663

[mmorearty]

Thanks for the links, @Veetaha, that's interesting. But I don't think my issue is directly related to #30663, because of the version where the slowdown started. That issue is a new one that appeared in 3.4.1. I just did some testing with old versions, and the slowdown for my issue was introduced all the way back in 2.6.1 (a very long time ago).

[richard-viney]

I've encountered what sounds like a similar performance issue in 3.4.5 that persists in 3.5-rc.

Repo to reproduce the problem is here: https://github.com/richard-viney/typescript-performance-issue

It's easy to get compilation times up into the 10-20-30 second mark or more just by duplicating a single line of code. There are two workarounds documented in the README, both related to generics.

Trying to reduce to a simpler self-contained repro case proved tricky, as reducing the amount of type definitions being pulled in also progressively reduced the performance problem, as if there was a scaling issue inside the compiler itself where internal lookup/resolution times aren't scaling as they should.

[richard-viney]

I should also add that we were stuck on 3.2.x for a while because of this issue, it originally cropped up in TS 3.3.0 and we've ended up working around it in our app code (by using fewer generics) so that we can stay on the latest TS release.