Build montage.js bootstrapping using a build script

[kriskowal]

⚠️ This depends on changes to mr in the corresponding build branch, which has not landed at time of writing. Changes to mop in the corresponding build branch are also required for compatibility. As such, the build branches of all of these repositories must be coordinated and land in a backward-incompatible release.

mr now includes a mrs script for building some stand-alone scripts based on Mr’s dependency analysis if the built modules only need the ability to require and export modules in a static working set. The resulting script has very little overhead for linking the modules. Lazy loading and compiler extensions are not supported, but would be possible with future work.

mrs is suitable for building the new Mr boot.js and the Montage boot script, montage.js. This change set introduces the command npm run build that updates montage.js and also produces boot/preload-boilerplate.js.

This introduces the need to rebuild montage.js whenever modules in the boot directory, mr, or any of their transitive dependencies are modified.

This obviates the need to perform script injection in montage.js, reducing code size and complexity in both development and production.

This obviates the need to have the packages checked into Git and the sub-repository update machinations that entails. These dependencies can be installed normally, with NPM. The relevant modules are incorporated into montage.js by the build script. Since mr and its dependencies now exist in node_modules, this obviates the need for Montage's package.json to use Mr-specific mappings or overlays.

This reduces the scope of montage.js to only need to support the browser script loading use case. It no longer needs to also serve as a Node.js module. It no longer needs to also serve as the boilerplate for bundling. These cases are now served in simpler and separate ways.

The parts of montage.js that were needed to bootstrap in Node.js are now in CommonJS modules in the boot directory. These are embeded in montage.js by the build script, but can also be used as Node.js modules without any wrappers or boilerplate.

The parts of montage.js that are needed to bootstrap in bundles built by Mop are now in boot/preload-boilerplate.js, which like montage.js is built using mrs.

This obviates the need to have a hard-coded copy of mr/mini-url.js. Mr and Montage can now share this CommonJS module instead of embedding it in their bootstrapping, which will make that function easier to maintain going forward. This also obviates the need for the mini-url dependency to be handled specially at run-time. Regardless of the platform, modules may depend on url. When used in a browser, the module system will link to mini-url.js. In Node.js, where mini-url.js would not work at all, it falls back to the url module provided by the platform.

When Mop prepares a bundle, it is now necessary for it to provide a data-location property instead of data-montage-location or data-mr-location since the code that handles this detection is now unified in mr/boot/script-params.js.

[kriskowal]

⚠️ I am not recommending this for merge onto master. This is a PR for review only at this time. When ready, it must land on a branch in preparation for a version in coordination with mr and mop. The mop portion is not ready at this time.

[rayshan]

Closing, will revisit when we decide to have a build step.

[hthetiot]

We going another direction.