feat: use packageManager from package.json as default bun version

[Copilot]

When no bun-version or bun-version-file input is provided, the action now automatically reads the bun version from package.json, falling back to latest if not found.

Changes

• Version resolution priority: bun-version input → bun-version-file input → package.json packageManager field → package.json engines.bun field → latest
• Silent mode for automatic checks: Added optional silent parameter to readVersionFromFile() to suppress warnings when automatically checking package.json
• Backward compatible: Existing workflows continue to work unchanged

Example

# Before: required explicit version
- uses: oven-sh/setup-bun@v2
  with:
    bun-version: latest

# After: reads from package.json automatically
- uses: oven-sh/setup-bun@v2

With package.json:

{
  "packageManager": "bun@1.0.25"
}

The action will now install Bun 1.0.25 without requiring explicit configuration.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>feat: make packageManager from package.json as default bun version</issue_title>
<issue_description>if packageManager doesn't exist, then latest</issue_description>

Comments on the Issue (you are @copilot in this section)

@xhyrom I think this makes perfect sense :)

• Fixes feat: make packageManager from package.json as default bun version #108

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[Copilot]

Pull request overview

This PR enhances the setup-bun action to automatically detect the Bun version from package.json when no explicit version is provided. The action now follows a priority chain: bun-version input → bun-version-file input → package.json packageManager field → package.json engines.bun field → latest. This makes the action more convenient to use while maintaining full backward compatibility.

Key Changes:

• Added automatic version detection from package.json as a fallback when no explicit version inputs are provided
• Introduced a silent parameter to readVersionFromFile() to suppress warnings during automatic version detection
• Added comprehensive test coverage for the new functionality

Reviewed changes

Copilot reviewed 4 out of 7 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/index.ts	Added automatic fallback to read Bun version from package.json with silent mode enabled
src/utils.ts	Enhanced readVersionFromFile function with optional silent parameter to suppress warnings during automatic checks
tests/utils.spec.ts	Added comprehensive test suite covering package.json version reading, silent mode behavior, and existing file format support
README.md	Updated documentation to reflect new default behavior and version resolution priority chain
package-lock.json	Version bump to 2.1.0 and compare-versions dependency entry (already used in codebase)

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