Rspack persistent cache bug repro

[slorber]

Here's a bug repro that shows a case where Rspack persistent cache is less efficient than webpack cache.

When some app JS files are code generated with fs.writeFile(), these files are always "re-loaded" by Rspack (but not by webpack) despite their content always being the same.

Not covered by this repro, but this also happens for files using loader this.addDependency("./dynamic.json"). I suspect the fs update time is used to invalidate cache entries, while webpack only uses the file content?

On Docusaurus, we have many files like that being code-generated, from JS to MDX documents outputted by community plugins. It would be great for us to have better persistent caching support for this scenario, like webpack does.

---

The test script yarn test will output:

###############################################
# USING WEBPACK
#############


##########
Bundle App start
- Loading src/entry.js
- Loading src/file.js
- Loading src/dynamicFile.js
Bundle App: 2.146s


##########
Bundle App start
Bundle App: 5.507ms


##########
Bundle App start
Bundle App: 4.528ms

###############################################
# USING RSPACK
#############


##########
Bundle App start
- Loading src/entry.js
- Loading src/file.js
- Loading src/dynamicFile.js
Bundle App: 2.032s


##########
Bundle App start
- Loading src/dynamicFile.js ===========> BAD
Bundle App: 1.009s


##########
Bundle App start
- Loading src/dynamicFile.js ===========> BAD
Bundle App: 1.006s

---

As you can see, the dynamicFile.js (code-generated) is always reloaded by Rspack, but not by webpack.