`import.meta.url` plugin is very slow for large files

[whitequark]

Consider this example: import-meta-url-slow.zip

With source maps disabled, adding metaUrlPlugin() increases runtime from ~80ms to ~1200ms; with source maps enabled, it is ~120ms to ~3400ms. Given that using this plugin also causes every page load to cause potentially multiple rebuilds, the resulting experience is quite awful.

To be clear, I do actually use import.meta.url in the problematic large files. I am not sure why exactly it is slow: while the resource*.js files are fairly large, most of the size is concentrated in a few strings. By any chance, are you repeatedly replacing a part of a JS string? (I haven't profiled it.)

[edoardocavazza]

The esbuild-plugin-meta-url parses all files which contain an import.meta.url expression using the oxc-parser parser and manipulates text contents using @napi-rs/magic-string. Every time the the walker finds a import.meta.url expression, the process starts a new internal build. The rooms of improvements are many and vary 😅

Are you using this plugin to import assets files or other source files?

[whitequark]

Are you using this plugin to import assets files or other source files?

I am using it to consolidate JS and related assets generated from C/C++ applications. They are rather sizable.

$ du -hsc dist/
274M    dist/
$ du -hsc dist/*.js
596K    dist/app.js
4.0K    dist/isolate.js
1.5M    dist/pyodide.asm.js
3.4M    dist/worker.js
5.4M    total

The worker.js includes the runtimes for 5-6 C++ applications of various size as well as their embedded filesystem blobs, which I really want to bundle into one download for simplicity of deployment and performance, and app.js includes the Pyodide runtime among others, with similar reasoning. All of this relies on new URL('.../relative-path', import.meta.url) in several different ways (the worker entry point is one, but more importantly this is how the C++ applications are downloading their assets; not doing this bundling step would result in a broken application).

You can check out the app at https://github.com/GlasgowEmbedded/webusb, it's easy to build.

Despite the somewhat terrifying total size numbers, the total network transfer size is about 15 MB (this data compresses really well), and the JS heap doesn't grow over 400 MB even after compiling and running all of the Wasm applications. So I think this is a reasonable use for a bundler.