tools: skip common extensions on js2c

[anonrig]

Reduces system calls on js2c.cc for IsDirectory function by eliminating .js and .mjs extensions.

cc @nodejs/cpp-reviewers

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/57948/

[joyeecheung]

What happens if someone accidentally create a directory that ends with .js or .mjs? Does this actually make enough difference in the build time to stop guarding against it?

[anonrig]

What happens if someone accidentally create a directory that ends with .js or .mjs? Does this actually make enough difference in the build time to stop guarding against it?

I think it's highly unlikely for someone to create a folder ending with .js, but I see your point. How can I benchmark this @joyeecheung @lemire? Any suggestions?

[lemire]

I would benchmark IsDirectory. It should be 'easy' to write a benchmark.

Here is what I would in practical terms.

1. Compare head-to-head with Bun and Deno. If everything is right, then they should all performance more or less the same.
2. Do syscall tracing (e.g.. dtruss under macOS). They should all do the same syscalls.

Since Node uses C++17, you can just do std::filesystem::is_directory. This may or may not be a good idea.

[joyeecheung]

It seems to be an overkill microbenchmarking a utility that’s only used at build time? Shouldn’t the only metrics that matter be the % of build time this reduces?

Note that, this was ported from a >10x slower Python script that had been used for many years and even then nobody really cared how slow it was….(and I think during development many people just use the configure option to load the scripts from disk, and skip JS2C entirely)

[joyeecheung]

Also to benchmark it, I would just

git checkout pr_branch
./configure --ninja
ninja -C out/Release node
rm out/Release/gen/node_javascript.cc
time ninja -C out/Release node # data point 1
git checkout main
rm out/Release/gen/node_javascript.cc
time ninja -C out/Release node # data point 2

(Using make works too. Just make sure that you don't set --node-builtin-modules-path when you configure, because that just let the build skips JS2C entirely...even though quite a few contributors use this, I believe).