When handling the null type change introduced by4.0, I deleted the old branches instead of gating them behind a version check. This PR just gates the old logic for< 4.0.

We don't have automated testing against old TS versions yet (#1752) so I tested this by hand by doing the following:

yarn build to build against4.0.0-beta.
change theresolved ts version to3.9.7
yarn install --ignore-scripts (the automatic rebuild after the install would fail due to incorrect types)
cd packages/typescript-estree && yarn test ast-fixtures
inspected the test output to ensure the only failures were due to fixtures for 4.0 features.

cc@thorn0 /@fisker

fix(typescript-estree): correct AST regression introduced by TS4.0 up…

074abfa

…grade

bradzacher added the bugSomething isn't working label

Jul 21, 2020

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typescript-eslintbot commentedJul 21, 2020

Thanks for the PR,@bradzacher!

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bradzacher mentioned this pull request

Jul 21, 2020

Add automated regression testing against old TS versions#1752

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codecovbot commentedJul 21, 2020•
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Codecov Report

Merging#2316 intomaster willdecrease coverage by0.01%.
The diff coverage is80.00%.

@@            Coverage Diff             @@##           master    #2316      +/-   ##==========================================- Coverage   93.10%   93.09%   -0.02%==========================================  Files         283      284       +1       Lines        9081     9092      +11       Branches     2493     2495       +2     ==========================================+ Hits         8455     8464       +9- Misses        301      302       +1- Partials      325      326       +1

Flag	Coverage Δ
#unittest	`93.09% <80.00%> (-0.02%)`	⬇️

Flags with carried forward coverage won't be shown.Click here to find out more.

Impacted Files	Coverage Δ
packages/typescript-estree/src/node-utils.ts	`96.72% <50.00%> (-0.02%)`	⬇️
packages/typescript-estree/src/convert.ts	`98.35% <60.00%> (-0.27%)`	⬇️
packages/typescript-estree/src/version-check.ts	`100.00% <100.00%> (ø)`