fix(commonjs)!: Correctly infer module name for any separator

[pastelmind]

Rollup Plugin Name: commonjs

This PR contains:

• bugfix
• feature
• refactor
• documentation
• other

Are tests included?

• yes (bugfixes and features will not be merged without tests)
• no

Breaking Changes?

• yes (breaking changes will not be merged unless absolutely necessary)
• no

If yes, then include "BREAKING CHANGES:" in the first commit message body, followed by a description of what is breaking.

List any relevant issue numbers: #923

Description

When a module whose file name is index.js is resolved to a module ID containing a directory separator that is different from path.sep of the current platform, the commonjs plugin incorrectly infers the base name of the module. This causes the absolute path of the module to be embedded into the bundle, and prevents generating reproducible builds across different machines.

For example, with a module ID of C:/Users/Phil/Documents/GitHub/test-vite-app/node_modules/react/index.js on Windows, the plugin generates code like this:

var C__Users_Phil_Documents_GitHub_testViteApp_node_modules_react = { exports: {} };
var react_production_min = {};

This PR fixes the problem by using path.basename() to extract the final path component instead of splitting the string with path.sep.

With the fix, the plugin generates code like this:

var react = { exports: {} };
var react_production_min = {};

Closes #923

[pastelmind]

I added a test. Unfortunately, it works only on Windows, where replacing backslashes with slashes is perfectly fine. On Linux, the backslash is treated as a regular character, which means that we'd get an error if we replaced slashes with backslashes.

[pastelmind]

@danielgindi I apologize for pinging you, but this PR hasn't even got a chance to run workflows yet. Could you please take a look?

[pastelmind]

@danielgindi Thanks for letting the CI workflow happen, but it failed and I'm not sure why. The log is at https://github.com/rollup/plugins/runs/3150391648, here's an excerpt:

Run pnpm run ci:test --filter ...[36a461e]
pnpm run ci:test --filter ...[36a461e]
shell: C:\Program Files\PowerShell\7\pwsh.EXE -command ". '{0}'"
 ERROR  Filtering by changed packages failed. fatal: bad object 36a461e
Error: Process completed with exit code 1.

I rebased the commit onto the current master and force-pushed, but now the workflow needs approval again. I'm not familiar with the CI process--could you please help me troubleshoot this?

[shellscape]

@pastelmind looks like your tests all pass now. I've requested review from a few folks to get eyes on this for you.

[danielgindi]

To me this looks much more resilient than the current code. Using core path functions handles this stuff for us.

[shellscape]