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docs: build system transpilers and loaders docs

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Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>
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Patrik Oldsberg
2022-01-16 15:05:58 +01:00
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docs/local-dev/cli-build-system.md
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@@ -258,8 +258,8 @@ frontend configuration to the bundle as `process.env.APP_CONFIG` and build
information as `process.env.BUILD_INFO`, and lastly minification handled by
[esbuild](https://esbuild.github.io/) using the
[`esbuild-loader`](https://npm.im/esbuild-loader). There are of course also a
set of loaders configured, which is covered in the
[transpilation section](#loaders-and-transpilation).
set of loaders configured, which you can read more about in the
[transpilation](#transpilation) and [loaders](#loaders) sections.
The output of the bundling process is split into two types of files. The first
is a set of generic assets with plain names in the root of the `dist/` folder.
@@ -344,4 +344,71 @@ RUN tar xzf bundle.tar.gz && rm bundle.tar.gz
CMD ["node", "packages/backend"]
```
## Loaders and Transpilation
## Transpilation
The transpilers used by the Backstage CLI have been chosen according to the
design considerations that we mentioned above. A few specific requirements are
of course support for TypeScript and JSX, but also React hot reloads or refresh,
and hoisting of Jest mocks. The Backstage CLI also only targets up to date and
modern browsers, so we actually want to keep the transpilation process as
lightweight as possible, and leave most syntax intact.
Apart from these requirements, we choose transpilers based on their speed. The
build process keeps the integration with the transpilers lightweight, without
additional plugins or such. This enables us to switch out transpilers as new
options and optimizations become available, and use the fastest options that are
available.
Our current selection of transpilers are [esbuild][https://esbuild.github.io/]
and [Sucrase](https://github.com/alangpierce/sucrase). The reason we choose to
use two transpilers is that esbuild is faster than Sucrase and produces slightly
nicer output, but it does not have the same feature set, and for example does
not support React hot reloading or hoisting of Jest mocks.
The benchmarking of the various options has been done in the
[ts-build-bench](https://github.com/Rugvip/ts-build-bench) project. It allows
for setups of different shapes and sizes of monorepos, but the setup we consider
the most important during benchmarking is a large monorepo with lots of medium
to large packages that's being bundled with Webpack. Some rough findings have
been that esbuild is the fastest option right now, with Sucrase following
closely after and then [SWC](https://swc.rs/) closely after that. After those
there's a pretty big gap up to the TypeScript compiler run in transpilation only
mode, and lastly another jump up to Babel, being by far the slowest.
Something to note about these benchmarks is that they take the full Webpack
bundling time into account. This means that even though some transpilation
options may be orders of magnitude faster than others, the total time is not
impacted in the same way as there's a lot of other things that go into the
bundling process. Still, switching from for example Babel to Sucrase is able to
make the bundling anywhere from two to five times faster.
## Loaders
The Backstage CLI is configured to support a set of loaders throughout all parts
of the build system, including the bundling, tests, builds, and type checking.
Loaders are always selected based on the file extension. The following is a list
of all supported file extensions:
| Extension | Exports | Purpose |
| ----------- | --------------- | ----------------------------------------------------------------------------- |
| `.ts` | Script Module | TypeScript |
| `.tsx` | Script Module | TypeScript and XML |
| `.js` | Script Module | JavaScript |
| `.jsx` | Script Module | JavaScript and XML |
| `.mjs` | Script Module | ECMAScript Module |
| `.cjs` | Script Module | CommonJS Module |
| `.json` | JSON Data | JSON Data |
| `.yml` | JSON Data | YAML Data |
| `.yaml` | JSON Data | YAML Data |
| `.css` | classes | Style sheet |
| `.eot` | URL Path | Font |
| `.ttf` | URL Path | Font |
| `.woff2` | URL Path | Font |
| `.woff` | URL Path | Font |
| `.bmp` | URL Path | Image |
| `.gif` | URL Path | Image |
| `.jpeg` | URL Path | Image |
| `.jpg` | URL Path | Image |
| `.png` | URL Path | Image |
| `.svg` | URL Path | Image |
| `.icon.svg` | React Component | SVG converted into a [MUI SvgIcon](https://mui.com/components/icons/#svgicon) |