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The MDX cross-compiler cache is an experimental feature introduced in #10479
It permits us to avoid transforming twice the same MD/MDX source file for both client/server environments.
It takes the assumption that both environments will compile exactly the same. This is mostly true, apart from a tiny detail that led to broken images in productions: inline file loaders.
Since the MDX compilation for both envs is run in parallel, a file might be compiled in client or server mode depending on which env compilation started first and got cached. This leads to some image inline loaders to have ?emit=true or ?emit=false randomly for the client-side app, while we always want it to have ?emit=true.
The solution implemented here is a bit complex but fixes our image problem. The idea is to always give priority to the client compilation as the source of truth. Even if the server compilation starts sooner, it will "wait" for the client compilation and use its result.
⚠️But there's a catch! This also means that now, our server environment will use ?emit=true, which will lead to images being emitted in build/__server/assets/images. It's not a big deal in practice: the __server folder is deleted in the build process, and it doesn't have a significant perf impact. We'll try to get rid of these inline loaders later but we can ship with this solution now.
Note: the impact of cross-compiler cache is quite significant, particularly more visible under Rspack where bundling goes from ~10s to ~7s. It's more significant than what we lose by emitting useless image assets.
Test Plan
CI + Argos + deploy preview
I'm not sure how to easily unit-test this 😅 . It's experimental for now, we'll figure out a way later if the experiment is successful.
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ArgosAdd this label to run UI visual regression tests. See argos.yml GH action.CLA SignedSigned Facebook CLApr: bug fixThis PR fixes a bug in a past release.
2 participants
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slorber
added
pr: bug fix
Motivation
Fix #10544
The MDX cross-compiler cache is an experimental feature introduced in #10479
It permits us to avoid transforming twice the same MD/MDX source file for both client/server environments.
It takes the assumption that both environments will compile exactly the same. This is mostly true, apart from a tiny detail that led to broken images in productions: inline file loaders.
Since the MDX compilation for both envs is run in parallel, a file might be compiled in client or server mode depending on which env compilation started first and got cached. This leads to some image inline loaders to have
?emit=trueor?emit=falserandomly for the client-side app, while we always want it to have?emit=true.The solution implemented here is a bit complex but fixes our image problem. The idea is to always give priority to the client compilation as the source of truth. Even if the server compilation starts sooner, it will "wait" for the client compilation and use its result.
?emit=true, which will lead to images being emitted inbuild/__server/assets/images. It's not a big deal in practice: the__serverfolder is deleted in the build process, and it doesn't have a significant perf impact. We'll try to get rid of these inline loaders later but we can ship with this solution now.Note: the impact of cross-compiler cache is quite significant, particularly more visible under Rspack where bundling goes from ~10s to ~7s. It's more significant than what we lose by emitting useless image assets.
Test Plan
CI + Argos + deploy preview
I'm not sure how to easily unit-test this 😅 . It's experimental for now, we'll figure out a way later if the experiment is successful.
Test links
https://deploy-preview-10553--docusaurus-2.netlify.app/