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Bump TypeScript to 5.9.#5550

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eliw00d wants to merge 12 commits intomicrosoft:mainfrom
eliw00d:ts-5.9
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Bump TypeScript to 5.9.#5550
eliw00d wants to merge 12 commits intomicrosoft:mainfrom
eliw00d:ts-5.9

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@eliw00d eliw00d commented Jan 13, 2026

Summary

Fixes #5544

Details

Based on #5157.

How it was tested

Impacted documentation

@github-project-automation github-project-automation bot moved this to Needs triage in Bug Triage Jan 13, 2026
@eliw00d eliw00d changed the title Ts 5.9 Bump TypeScript to 5.9. Jan 13, 2026
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eliw00d commented Jan 13, 2026

@microsoft-github-policy-service agree company="Calm"

"compilerOptions": {
"outDir": "lib",
"rootDir": "src",
"skipLibCheck": true,
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This seemed like the least invasive way to resolve the build issue related to api-extractor. If there's a better way, let me know!

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What's the issue that shows up without this?

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If I have time this week I'll fix this PR up and look at removing this.

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I tried a few things but it seems like the heft-typescript-v3-test + typescript@5.9 + @types/node@17 don't work well together and setting skipLibCheck to true was the only way to avoid the new 5.9 types from conflicting.

"compilerOptions": {
"outDir": "lib",
"rootDir": "src",
"skipLibCheck": true,
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What's the issue that shows up without this?

@iclanton iclanton moved this from Needs triage to In Progress in Bug Triage Jan 26, 2026
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+1

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Also would resolve #5052 #5319

…lugin/ts-5.9_2026-01-13-22-17.json

Co-authored-by: Ian Clanton-Thuon <iclanton@users.noreply.github.com>
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Successfully merging this pull request may close these issues.

[heft] The TypeScript compiler version 5.9.3 is newer than the latest version that was tested with Heft (5.8); it may not work correctly.

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