Add simpler mechanism for define new JS preprocessor functions/macros.

[sbc100]

Currently we have a fixed set of processor macros/function that are mostly defined in parseTools.js

Adding new macros in JS libraries is possible, but its rather ugly syntax, and has some limitations:

{{{
globalThis.newMacro = () = { .. }
}}}

A major drawback (IIUC) of doing this is that the macros are not available during preprocessing since macros expansion happens after preprocessing. So to use these macros in a preprocessor directive one would need define them in a separate file that is loaded first. e.g. --js-library=my_macros.js --js-library=my_library.js. Here the macros defined in my_macros.js would be available in my_library.js.

One way to improve this would be to allow my_library.js to somehow #include "my_macros.js" .. however that isn't currently how the #include directive works. Currently #include files are placed directly into the output file and don't have macros expanded, so we would need somekind of new #include mechanism.

[adamscott]

Here's a my_macros.js file that enables semver checks in library files.

// my_macros.js
/* eslint-disable */
{{{
/* eslint-enable */
	globalThis.___EMSCRIPTEN_VERSION_PARSED = globalThis.EMSCRIPTEN_VERSION.split('.').map((n) => parseInt(n, 10));

	globalThis.___SEMVER_IS_GREATER_THAN = (a, b, { orEqual = false } = {}) => {
		const [aMajor, aMinor, aPatch] = a;
		const [bMajor, bMinor, bPatch] = b;
		if ((orEqual && aMajor >= bMajor) || aMajor > bMajor) {
			if ((orEqual && aMinor >= bMinor) || aMinor > bMinor) {
				if ((orEqual && aPatch >= bPatch) || aPatch > bPatch) {
					return true;
				}
			}
		}
		return false;
	};

	globalThis.EMSCRIPTEN_VERSION_IS_GREATER_THAN = (major, minor, patch) => {
		const isGreater = globalThis.___SEMVER_IS_GREATER_THAN(globalThis.___EMSCRIPTEN_VERSION_PARSED, [major, minor, patch]);
		return isGreater;
	};

	globalThis.EMSCRIPTEN_VERSION_IS_GREATER_THAN_OR_EQUAL = (major, minor, patch) => {
		const isGreaterOrEqual = globalThis.___SEMVER_IS_GREATER_THAN(globalThis.___EMSCRIPTEN_VERSION_PARSED, [major, minor, patch], { orEqual: true });
		return isGreaterOrEqual;
	};

	globalThis.EMSCRIPTEN_VERSION_IS_LESS_THAN = (major, minor, patch) => {
		const isGreaterOrEqual = globalThis.___SEMVER_IS_GREATER_THAN(globalThis.___EMSCRIPTEN_VERSION_PARSED, [major, minor, patch], { orEqual: true });
		return !isGreaterOrEqual;
	};

	globalThis.EMSCRIPTEN_VERSION_IS_LESS_THAN_OR_EQUAL = (major, minor, patch) => {
		const isGreater = globalThis.___SEMVER_IS_GREATER_THAN(globalThis.___EMSCRIPTEN_VERSION_PARSED, [major, minor, patch]);
		return !isGreater;
	};
/* eslint-disable */
}}}
/* eslint-enable */

Then, you can use the macros like this inside your library:

// library_mylib.js
const GodotWebXR = {
	$GodotWebXR__deps: [
#if EMSCRIPTEN_VERSION_IS_LESS_THAN(3,1,71)
		'$Browser',
#else 
		'$MainLoop',
#endif
		'$GL', 
		'$GodotRuntime', 
		'$runtimeKeepalivePush', 
		'$runtimeKeepalivePop'
	]
	$GodotWebXR: {
	}
}

[sbc100]

Thats a good example of how things work today yes. This proposal is to make the mechanism official blessed and to enable library_mylib.js to reference my_macros.js internally so that users don't need to explicitly add both on the command line (in the right order).