Preserve Maven toolchains across repeated setup-java runs (#1099)

[brunoborges]

Summary

Fixes #1099. Running setup-java multiple times in the same job (matrix builds or multiple java-version values) could drop toolchain entries registered by earlier runs, leaving only one JDK in ~/.m2/toolchains.xml.

Root cause

Toolchains generation was gated behind the overwrite-settings input. When overwrite-settings: false, writeToolchainsFileToDisk skipped writing entirely if the file already existed — so a second setup-java run never persisted its JDK, silently discarding the merged result.

This gating was inappropriate because:

• overwrite-settings is documented (in action.yml) to control regeneration of settings.xml only.
• generateToolchainDefinition already performs a non-destructive merge: existing JDK, custom, and user-managed toolchains are preserved, and only an entry with the exact same type + provides.id is replaced.

So writing the toolchains file is always safe and should not be blocked.

Changes

• src/toolchains.ts: Remove overwriteSettings from configureToolchains, createToolchainsSettings, and writeToolchainsFileToDisk. The toolchains file is now always written (non-destructively). settings.xml behavior in auth.ts is unchanged.
• __tests__/toolchains.test.ts: Update call sites, rewrite the "does not overwrite" test to assert non-destructive extension, and add a regression test that runs configureToolchains three times and asserts every JDK is preserved with no duplicates.
• docs/advanced-usage.md: Clarify that the merge is non-destructive and independent of overwrite-settings.
• dist/setup/index.js: Rebuilt.

Testing

• npm run build, npm run format-check, npm run lint all pass.
• npm test: 909 passing, including the new regression test.

Co-authored-by: Copilot App 223556219+Copilot@users.noreply.github.com

[Copilot]

Pull request overview

This PR fixes a regression where running actions/setup-java multiple times within the same job could cause Maven ~/.m2/toolchains.xml to lose previously-registered JDK toolchain entries. It makes toolchains persistence independent of the overwrite-settings input (which is intended to control settings.xml only), relying on the existing non-destructive merge behavior when generating toolchains.

Changes:

• Always write toolchains.xml after merging, regardless of overwrite-settings.
• Update and expand toolchains tests, including a multi-run regression test ensuring all JDK entries are preserved without duplicates.
• Clarify the non-destructive merge behavior in advanced usage docs; rebuild dist.

Show a summary per file

File	Description
src/toolchains.ts	Removes overwrite-settings gating so toolchains are always persisted after merge.
__tests__/toolchains.test.ts	Updates call sites and adds regression coverage for repeated runs preserving all toolchains.
docs/advanced-usage.md	Documents that toolchains merging is non-destructive and independent of overwrite-settings.
dist/setup/index.js	Rebuilt distribution output reflecting the source changes.

Review details

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• Files reviewed: 3/4 changed files
• Comments generated: 2
• Review effort level: Low

[brunoborges]

@lmvysakh can you please review this?

[mhoffrog]

@brunoborges This PR will raise a conflict to my #1109 one I guess.
=> #1109 will have to await this one being merged. I will take care of updating myone after this one has been merged.
=> I will put #1109 to draft now and will re-wake it later.

[lmvysakh]

Hy @brunoborges ,

Reviewed and Approved PR.