Fix build failures when any parent directory is {"type": "module"}

[shamrin]

Fix hard-to-debug failures when any parent directory has package.json with {"type": "module"}.

Before this fix emconfigure / conftest would fail with an error in config.log, and prevent the build from succeeding:

TypeError [ERR_UNKNOWN_FILE_EXTENSION]: Unknown file extension ""

To fix the problem, we add .cjs extension to generated Node scripts, forcing commonjs mode. In addition, we add a shell wrapper that calls node with this script, to make autoconf happy. Autoconf does not expect its conftest binary to have an extension.

Other solutions:

1. Pass script content via stdin. It should force Node to commonjs mode. See --input-type=commonjs documentation. Not good, the scripts would not to be able to access stdin anymore.
2. Run echo '{"type":"commonjs"}' > package.json in the build directory. Simple, but not good if the build directory has its own package.json already.
3. Custom loader via --experimental-loader parameter. It works, but the feature is unstable and depends on Node version.

Related Node issues:

• node should execute files without extension as ESM if "type": "module", is specified nodejs/node#34049
• Allow flexible node script names in esm nodejs/node#37512

fixes #13551
fixes #17431

[shamrin]

@sbc100 What do you think about the general direction of this fix? I've added some details in the PR description.

[thomasballinger]

What's the conftest-like usage in option 3? .cjs sounds most explicit, but also like a larger change.

[shamrin]

@thomasballinger:

What's the conftest-like usage in option 3? .cjs sounds most explicit, but also like a larger change.

It looks like Emscripten creates a conftest "executable" at some point during the (autoconf?) build. I think the build process expects it to be named conftest, without extension.

But I'm not 100% sure. Emscripten is magical :-)

[sbc100]

@thomasballinger:

What's the conftest-like usage in option 3? .cjs sounds most explicit, but also like a larger change.

It looks like Emscripten creates a conftest "executable" at some point during the (autoconf?) build. I think the build process expects it to be named conftest, without extension.

But I'm not 100% sure. Emscripten is magical :-)

This is not emscripten, but autoconf which like to make executables with this name and without and extension by default. I think this whole issue only really effects autoconf users since other users.

One option is to try to persuade autoconf to use an extension when building executables like this.

[shamrin]

@sbc100 I've implemented your shell wrapper idea from #17431 (comment). It does work.

[sbc100]

Can you just to shutil.rename(script, cjs_script).. this avoid the need for the read_file above.

[sbc100]

I think we only want to do this if the name of the output file does not have an extension already. e.g. conftest. If the user does -o out.js it would be a little odd to have out.js be shell script that runs out.cjs.

So I think maybe we need both old and new methods. You can do if not shared.suffix(script): to check this.

[dsogari]

The issue can be circumvented by setting the ac_cv_exeext variable when invoking the configure script, like so:

ac_cv_exeext=.cjs emconfigure ...

This also configures the EXEEXT variable used in make check. I'm not aware of any documentation for this feature, but I've tested it with GNU Autoconf 2.71.

Perhaps the emconfigure script could incorporate this fix, so users don't need to worry about it?

[dsogari]

An alternative is to create a package.json file in the build directory with an empty configuration, like so: {}.