When was constraintDepth added?

[AnyhowStep]

I was testing some of my code in TS 3.6 and TS 3.7

Code that worked fine in TS 3.5.1 now got the Type_instantiation_is_excessively_deep_and_possibly_infinite error instead.

I decided to do a little investigation and noticed that there was this thing called constraintDepth with a limit of 50. This was what was triggering the error.

I tried to disable the check for this constraintDepth and, predictably, got the error,

                return mapper(type);
                       ^
RangeError: Maximum call stack size exceeded
    at instantiateTypeWorker (/home/anyhowstep/node-projects/tsql/tsql/node_modules/typescript/lib/typescript.js:42582:24)
    at instantiateType (/home/anyhowstep/node-projects/tsql/tsql/node_modules/typescript/lib/typescript.js:42575:26)
    at /home/anyhowstep/node-projects/tsql/tsql/node_modules/typescript/lib/typescript.js:42274:42
    at Object.map (/home/anyhowstep/node-projects/tsql/tsql/node_modules/typescript/lib/typescript.js:507:29)
    at getConditionalTypeInstantiation (/home/anyhowstep/node-projects/tsql/tsql/node_modules/typescript/lib/typescript.js:42537:40)
    at instantiateTypeWorker (/home/anyhowstep/node-projects/tsql/tsql/node_modules/typescript/lib/typescript.js:42620:24)
    at instantiateType (/home/anyhowstep/node-projects/tsql/tsql/node_modules/typescript/lib/typescript.js:42575:26)
    at /home/anyhowstep/node-projects/tsql/tsql/node_modules/typescript/lib/typescript.js:42274:42
    at Object.map (/home/anyhowstep/node-projects/tsql/tsql/node_modules/typescript/lib/typescript.js:507:29)
    at getConditionalTypeInstantiation (/home/anyhowstep/node-projects/tsql/tsql/node_modules/typescript/lib/typescript.js:42537:40)
    at instantiateTypeWorker (/home/anyhowstep/node-projects/tsql/tsql/node_modules/typescript/lib/typescript.js:42620:24)
    at instantiateType (/home/anyhowstep/node-projects/tsql/tsql/node_modules/typescript/lib/typescript.js:42575:26)
    at /home/anyhowstep/node-projects/tsql/tsql/node_modules/typescript/lib/typescript.js:42274:42
    at Object.map (/home/anyhowstep/node-projects/tsql/tsql/node_modules/typescript/lib/typescript.js:507:29)
    at getConditionalTypeInstantiation (/home/anyhowstep/node-projects/tsql/tsql/node_modules/typescript/lib/typescript.js:42537:40)
    at instantiateTypeWorker (/home/anyhowstep/node-projects/tsql/tsql/node_modules/typescript/lib/typescript.js:42620:24)

However, if the code I wrote really was the problem, it shouldn't have run fine in 3.5.1. It should have also exceeded the max call stack size.

---

I don't have a minimal repro but I noticed something weird.
The following exceeds the constraint depth on 3.6 and 3.7,

However, the following does not,

Trying to nest function calls directly triggers the constraint depth error. But assigning it to a temporary variable is OK.

---

I'm a bit at a loss here and out of my depth (haha, depth).

• When was constraintDepth added?
• Why was it added?
• What problem was it trying to solve?

Code that worked fine in TS 3.5.1 now hits this constraintDepth error.
Removing the limit causes the max call stack size to be exceeded.

So, it looks to me like there's a bug with the code surrounding the constraintDepth implementation. Hopefully, the answers to my questions can help me refactor my code to not hit the depth limit. Or maybe it'll expose a bug that needs fixing in the TS code base.

[AnyhowStep]

The file with the problem may be found here,
AnyhowStep/tsql@c413c11#diff-dfb1d0c2f356726e8bd4741b3ba718daR12-R29

1. Clone https://github.com/AnyhowStep/tsql
2. cd tsql
3. Checkout c413c1152ae7b65eb2e2a18ee985d6dbb8b31295
4. npm install
5. npm run test ./test/run-time/input/expr-library/double/acos/double.ts

I'd like to again stress that this runs fine on TS 3.5.1 =(

[jack-williams]

#26558

44ada08

[AnyhowStep]

Also, further proof the functions in question are fine on TS 3.5.1,

AnyhowStep/tsql@f9b73b2#diff-39b2092b0dd378cba12e94f7af61aba7R11-R573
In the above linked file, I've nested acos() and coalesce() calls 100+ times (500+ lines).

The emit of that giant file is here (only 30+ lines),
AnyhowStep/tsql@f9b73b2#diff-925d183e2fe29d7d151e0add12f6e4eeR2-R36

That file and 500+ others only take 27s to compile with TS 3.5.1,

A screenshot of the file with 100+ nested function calls,

[AnyhowStep]

Thanks, @jack-williams , I'll start looking from there.

[typescript-bot]

This issue has been marked as 'Question' and has seen no recent activity. It has been automatically closed for house-keeping purposes. If you're still waiting on a response, questions are usually better suited to stackoverflow.

[AnyhowStep]

Instead of trying to figure out which commit broke my TypeOfCoalesce<> recursive type, I decided to just convert it into a trampoline.

The PR on my project,
AnyhowStep/tsql#65

The file that has the new TypeOfColaesce<> type,
https://github.com/AnyhowStep/tsql/pull/65/files#diff-0214b2fefabaf1617e690660683db775R226-R237

If anyone else is running into max depth errors with recursive types, trampolines may be a viable solution.

Here's another example of trampolines being used,
https://github.com/AnyhowStep/tsql/blob/master/src/tuple-util/reverse.ts