fix: support cross compiling for wasm with make generator

[toyobayashi]

• Context: Question about cross compile Node-API addon to wasm with emnapi and emscripten on Windows/macOS node-gyp#2823
• Test Repo: https://github.com/toyobayashi/emnapi-node-gyp-test

I'm not sure if it's reasonable to do such changes, but it works!

[toyobayashi]

In fact the generated file path in makefile is still incorrect on Windows, users need to use a additional script to make it work

const path = require('path')
const fs = require('fs')

const buildDir = path.join(__dirname, '../build')

fs.readdirSync(buildDir)
  .filter(p => p.endsWith('.target.mk'))
  .map((p) => path.join(buildDir, p))
  .forEach((p) => {
    const content = fs.readFileSync(p, 'utf8').replace(/\\|\\\\/g, '/').replace(/\/(\r?\n)/g, '\\$1')
    fs.writeFileSync(p, content, 'utf8')
  })

I'm not familiar the gyp code base, it will be nice if you could help make node-gyp more friendly for building wasm🙏

[toyobayashi]

In fact the generated file path in makefile is still incorrect on Windows, users need to use a additional script to make it work

with changes in 882c1f9, the additional script is no longer required in my minimum test project

• https://github.com/toyobayashi/emnapi-node-gyp-test/blob/e424920e8006429e842aa47dafc001b93c80e03d/patches/node-gyp.patch
• https://github.com/toyobayashi/emnapi-node-gyp-test/actions/runs/7628601442

not sure if self.WriteLn or somewhere also need to apply the ReplaceSep

[toyobayashi]

@cclauss want to ask a question that may be not related to this PR, how can I get the absolute path of .gypi in itself?

The emcc --js-library flag can receive an absolute or relative path (relative to cwd) of a JavaScript library file to link against. If I set a relative path in common.gypi,

# ${projectRoot}/node_modules/emnapi/common.gypi
{
  'target_defaults': {
    'target_conditions': [
      ['_type=="executable"', {
        'conditions': [
          ['OS == "emscripten"', {
            'libraries': [
               # expect "${projectRoot}/node_modules/emnapi/dist/library_napi.js"
              '--js-library=./dist/library_napi.js',
            ],
          }],
        ],
      }],
    ],
  },
}

it doesn't work when running node-gyp build because the relative path is not handled by gyp, the cwd is ${projectRoot}/build so emscripten will find the path in ${projectRoot}/build/dist/library_napi.js, that is incorrect.

I tried defining a variable that invoke Node.js's require to locate the correct absolute path

'variables': {
  'emnapi_js_library%': '<!(node -p "(()=>{try{return require(\'emnapi\').js_library}catch(e){return \'\'}})()")'
},

But this is not reliable, The package found by require('emnapi') is not necessarily the package where common.gypi is currently located, also may enter the error path if emnapi is not used via npm.

So I wonder if I can set the absolute path depend on common.gypi itself. So that I can write something like

{
  'libraries': [
    # like CMAKE_CURRENT_SOURCE_DIR
    '--js-library=<(SOURCE_DIR_OF_COMMONGYPI)/dist/library_napi.js',
  ],
}

in emnapi's common.gypi file.

[toyobayashi]

how can I get the absolute path of .gypi in itself?

I have found solution for this question.

I opened another PR nodejs/node-gyp#2974 in node-gyp repo to support rebuild and build commands on Windows. That and this one both are ready for review.

[toyobayashi]

Any other suggestions or change request?

[legendecas]

Overall LGTM.

[toyobayashi]

@cclauss I have added unit test. I believe you have read diff wrongly just now somehow. The subprocess.Popen() was inside GetCrossCompilerPredefines so I defined defines and return it. The whole function looks like this now, could you please take another look?

gyp-next/pylib/gyp/common.py

Lines 425 to 472 in 4bf22c4

	def GetCrossCompilerPredefines(): # -> dict
	CC = os.environ.get("CC_target") or os.environ.get("CC")
	CFLAGS = os.environ.get("CFLAGS")
	CXX = os.environ.get("CXX_target") or os.environ.get("CXX")
	CXXFLAGS = os.environ.get("CXXFLAGS")
	cmd = []
	defines = {}
	if CC:
	cmd += CC.split(" ")
	if CFLAGS:
	cmd += CFLAGS.split(" ")
	elif CXX:
	cmd += CXX.split(" ")
	if CXXFLAGS:
	cmd += CXXFLAGS.split(" ")
	else:
	return defines
	if sys.platform == "win32":
	fd, input = tempfile.mkstemp(suffix=".c")
	try:
	os.close(fd)
	out = subprocess.Popen(
	[*cmd, "-dM", "-E", "-x", "c", input],
	shell=True,
	stdout=subprocess.PIPE, stderr=subprocess.STDOUT
	)
	stdout = out.communicate()[0]
	finally:
	os.unlink(input)
	else:
	input = "/dev/null"
	out = subprocess.Popen(
	[*cmd, "-dM", "-E", "-x", "c", input],
	shell=False,
	stdout=subprocess.PIPE, stderr=subprocess.STDOUT
	)
	stdout = out.communicate()[0]
	lines = stdout.decode("utf-8").replace("\r\n", "\n").split("\n")
	for line in lines:
	if not line:
	continue
	define_directive, key, *value = line.split(" ")
	assert define_directive == "#define"
	defines[key] = " ".join(value)
	return defines

All tests in my project passed. https://github.com/toyobayashi/emnapi-node-gyp-test/actions/runs/8510349552/job/23307768601

[cclauss]

Sorry that I misread before.

[cclauss]

Nice work! Tests and all.

[legendecas]

Thanks!