Support installation from custom NPM registry via .npmrc

[Eynorey]

Related to #177.

This PR adds support for custom NPM registry configurations, allowing the action to install PNPM from there.

With this, the action reads a potential custom registry configuration from .npmrc if it exists, and uses the result by running the install script with a corresponding --registry <custom> flag.

# My custom registry
registry = https://my-registry.my-company.com/

Here are some scenarios I tested using this script:

Test Results

🧪 Testing readNpmrcRegistry function

📋 1. No .npmrc file
──────────────────────────────────────────────────
✅ PASS: Expected 'undefined', got 'undefined'

📋 2. Empty .npmrc file
──────────────────────────────────────────────────
[INFO] Reading .npmrc file from: /tmp/npmrc-test-gZgnMl/.npmrc
[DEBUG] No valid registry configuration found in .npmrc
✅ PASS: Expected 'undefined', got 'undefined'

📋 3. .npmrc without registry entry
──────────────────────────────────────────────────
[INFO] Reading .npmrc file from: /tmp/npmrc-test-gZgnMl/.npmrc
[DEBUG] No valid registry configuration found in .npmrc
✅ PASS: Expected 'undefined', got 'undefined'

📋 4. .npmrc with invalid registry entry
──────────────────────────────────────────────────
[INFO] Reading .npmrc file from: /tmp/npmrc-test-gZgnMl/.npmrc
[WARNING] Invalid registry URL format in .npmrc (must be http/https): invalid-url-without-protocol
[DEBUG] No valid registry configuration found in .npmrc
✅ PASS: Expected 'undefined', got 'undefined'

📋 5. .npmrc with one invalid and one valid registry entry
──────────────────────────────────────────────────
[INFO] Reading .npmrc file from: /tmp/npmrc-test-gZgnMl/.npmrc
[WARNING] Invalid registry URL format in .npmrc (must be http/https): invalid-url
[INFO] Using custom registry from .npmrc: https://npm.company.com/
✅ PASS: Expected 'https://npm.company.com/', got 'https://npm.company.com/'

📋 6. .npmrc with one valid and one scoped entry (scoped ignored)
──────────────────────────────────────────────────
[INFO] Reading .npmrc file from: /tmp/npmrc-test-gZgnMl/.npmrc
[INFO] Using custom registry from .npmrc: https://registry.npmjs.org/
✅ PASS: Expected 'https://registry.npmjs.org/', got 'https://registry.npmjs.org/'

📋 7. .npmrc with spaces around equals sign
──────────────────────────────────────────────────
[INFO] Reading .npmrc file from: /tmp/npmrc-test-gZgnMl/.npmrc
[INFO] Using custom registry from .npmrc: https://npm.example.com/
✅ PASS: Expected 'https://npm.example.com/', got 'https://npm.example.com/'

📋 8. .npmrc with trailing slash (should be preserved)
──────────────────────────────────────────────────
[INFO] Reading .npmrc file from: /tmp/npmrc-test-gZgnMl/.npmrc
[INFO] Using custom registry from .npmrc: https://npm.example.com/path/
✅ PASS: Expected 'https://npm.example.com/path/', got 'https://npm.example.com/path/'

📋 9. .npmrc with http (not just https)
──────────────────────────────────────────────────
[INFO] Reading .npmrc file from: /tmp/npmrc-test-gZgnMl/.npmrc
[INFO] Using custom registry from .npmrc: http://internal.npm.company.com/
✅ PASS: Expected 'http://internal.npm.company.com/', got 'http://internal.npm.company.com/'

📋 10. .npmrc with comments using semicolon
──────────────────────────────────────────────────
[INFO] Reading .npmrc file from: /tmp/npmrc-test-gZgnMl/.npmrc
[INFO] Using custom registry from .npmrc: https://npm.example.com/
✅ PASS: Expected 'https://npm.example.com/', got 'https://npm.example.com/'

Note

I was also considering an action parameter, but this feels more natural - if you are already using a custom registry via .npmrc, then you'll likely want your package manager to be fetched form there as well.

But I could also see a parameter being helpful for some setups, perhaps even acting as an override to the .npmrc registry configuration. Maybe as a follow-up?

Any feedback is greatly appreciated!

[benquarmby]

❤️ Love this.

My opinion doesn't matter a great deal, but I'm going to give it anyway 😜

[Eynorey]

@zkochan/@KSXGitHub would you mind taking a look when you get a chance, thanks!