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fix(eslint-plugin): [no-unnecessary-type-assertion] false positive on non-null assertion after an implicitly-any variable gets initialised inside conditional block#11082

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fix(eslint-plugin): [no-unnecessary-type-assertion] false positive on non-null assertion after an implicitly-any variable gets initialised inside conditional block#11082

mdm317 wants to merge1 commit intotypescript-eslint:mainfrommdm317:11054-no-unnecessary-type-assertion

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mdm317 commentedApr 16, 2025•
edited by kirkwaiblinger
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Caution

Currently blocked by#10334 /microsoft/TypeScript#60514. See#11082 (comment)

PR Checklist

Addresses an existing open issue:fixesBug: @typescript-eslint/no-unnecessary-type-assertion False positive on non-null assertion after an implicitly-any variable gets initialised inside a conditional or loop #11054
That issue was marked asaccepting prs
Steps inContributing were taken

Overview

I have updated it so thatisPossiblyUsedBeforeAssigned returnstrue when the variable is not explicitly typed at the time of declaration

fix: implicit any initialization in conditionals/loops

b568ec6

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typescript-eslintbot commentedApr 16, 2025

Thanks for the PR,@mdm317!

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mdm317 marked this pull request as draft

April 16, 2025 09:20

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View yourCI Pipeline Execution ↗ for commitb568ec6.

Command	Status	Duration	Result
`nx typecheck ast-spec`	✅ Succeeded	<1s	View ↗
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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.82%. Comparing base(f30a20e) to head(b568ec6).
Report is 17 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@##             main   #11082   +/-   ##=======================================  Coverage   90.82%   90.82%           =======================================  Files         497      497             Lines       50204    50206    +2       Branches     8274     8275    +1     =======================================+ Hits        45600    45602    +2  Misses       4589     4589             Partials       15       15

Flag	Coverage Δ
unittest	`90.82% <100.00%> (+<0.01%)`	⬆️

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

Files with missing lines	Coverage Δ
...-plugin/src/rules/no-unnecessary-type-assertion.ts	`98.99% <100.00%> (+<0.01%)`	⬆️

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mdm317 marked this pull request as ready for review

April 16, 2025 15:40

kirkwaiblinger reviewed

Apr 16, 2025

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packages/eslint-plugin/src/rules/no-unnecessary-type-assertion.ts

		) {
		if (declaration.type == null) {
		return true;

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We're definitely in the right ballpark, but I notice that this introduces a regression with the following case:

functionfoo(){letxif(Math.random()>0.5){x=3;}else{x=4;}// should be flagged as unnecessaryx!;}

I wonder if it's possible to get that case correct still? (it may or may not be feasible to prevent some false positives or negatives)

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actually - I think you can ignore this regression... This is most likely a symptom of#10334 /microsoft/TypeScript#60514

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mdm317Apr 18, 2025•
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@kirkwaiblinger
Thanks for review! 🙏

The regression also occurs in this simplified case:

function foo() {  let x;  x =4;  // should be flagged as unnecessary  x!;}

This is most likely a symptom of#10334 /microsoft/TypeScript#60514

As you mentioned, it's not possible to fix that case for now.

Should I close this PR until that issue is resolved?

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Hmmm. I'm not sure which choice is the lesser of two evils here... fixing the bug at the cost of that rather undesirable-looking regression, or marking the bug as blocked. I'm gently leaning towards making this work as blocked unless we can find away to proceed while mitigating this regression 🤔 But then again if it was that important of a case, you'd think we might have a test case that caught it?

Looking for thoughts from @typescript-eslint/triage-team too.

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Yeah I don't really want to wade into these murky waters 🙃. +1 on marking as blocked.

kirkwaiblinger added the blocked by another issueIssues which are not ready because another issue needs to be resolved first label

May 5, 2025

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fix(eslint-plugin): [no-unnecessary-type-assertion] false positive on non-null assertion after an implicitly-any variable gets initialised inside conditional block#11082

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fix(eslint-plugin): [no-unnecessary-type-assertion] false positive on non-null assertion after an implicitly-any variable gets initialised inside conditional block#11082

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mdm317 commentedApr 16, 2025•
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