chore: bump TS to 3.7

[SimenB]

Summary

3.7 is out 🎉 I haven't actually tried to run this, just opening up a PR 😀

https://devblogs.microsoft.com/typescript/announcing-typescript-3-7/

Test plan

Green CI?

[jeysal]

Yeahhhhh that looks a lot like a TS bug https://circleci.com/gh/facebook/jest/73686?utm_campaign=vcs-integration-link&utm_medium=referral&utm_source=github-build-link

[SimenB]

It looks like a regression to me... @orta?

https://github.com/facebook/jest/blob/0fd5e3cdd80a866623f1f0cf2385fef38015d51f/packages/jest-circus/src/utils.ts#L101-L125

[G-Rath]

I had a quick look into this for my own learning, but the more I did, the more I couldn't explain it, and got sucked into; I think @jeysal might be right: this looks like it might be a bug in TS.

This fixes it:

export const getEachHooksForTest = (test: Circus.TestEntry) => {
    const result: {
        beforeEach: Array<Circus.Hook>;
        afterEach: Array<Circus.Hook>;
    } = { afterEach: [], beforeEach: [] };
    let block: Circus.DescribeBlock | undefined | null;

    do {
        block = test.parent;
        const beforeEachForCurrentBlock = [];

        for (const hook of block.hooks) {
            switch (hook.type) {
                case 'beforeEach':
                    beforeEachForCurrentBlock.push(hook);
                    break;
                case 'afterEach':
                    result.afterEach.push(hook);
                    break;
            }
        }
        // 'beforeEach' hooks are executed from top to bottom, the opposite of the 
        // way we traversed it. 
        result.beforeEach = [...beforeEachForCurrentBlock, ...result.beforeEach];
    } while (block.parent);
    return result;
};

Here's a Playground Link for easy playing around :)

[G-Rath]

Confirmed it's a bug in TS.

It's been fixed and merged into master.

You can work around it for now by just doing const hooks = block.hooks;

The root reason is that TS creates a circular reference itself in attempting to check for exhaustiveness 😬

[SimenB]

Thanks @G-Rath! I'll apply the workaround locally and push 👍

[SimenB]

Wait, what's the fix? const hooks = block.hooks; does't change anything, and the first thing you pasted always does block = test.parent; which would end up in a loop, no?

[G-Rath]

Wait, what's the fix? const hooks = block.hooks; doesn't change anything,

Sorry I should have been clearer: You don't use hooks - it's literally the assignment of the variable before the loop causes TS to use a slightly different analysis path that does't create a circular reference.

Alternatively, doing

        if (!block.hooks) {
            break;
        }

before the look would work too, and at least is doing something, even if it's a conditional that'll never be true.

the first thing you pasted always does block = test.parent; which would end up in a loop, no?

It shouldn't, b/c the do { block = block.parent; .... } while(block.parent) should mean it bails when the parent isn't defined.

I might have missed something, but that should be the unrolled version of do { ... } while ((block = block.parent))

I forgot that the first assignment is test.parent - my bad!

[SimenB]

Found a tweak that was relatively clean 🤞

[codecov-io]

Codecov Report

Merging #9145 into master will not change coverage.
The diff coverage is 0%.

@@           Coverage Diff           @@
##           master    #9145   +/-   ##
=======================================
  Coverage   64.83%   64.83%           
=======================================
  Files         278      278           
  Lines       11732    11732           
  Branches     2882     2882           
=======================================
  Hits         7607     7607           
  Misses       3508     3508           
  Partials      617      617

Impacted Files	Coverage Δ
packages/jest-circus/src/utils.ts	15.38% <0%> (ø)	⬆️

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