docs(tvix): update WASM status r/8344

crate2nix can now build WASM, and cl/11859 showcases this now.

Even if it's not in the same cargo workspace, we should still migrate
tvixbolt to a crate2nix build.

Remove the part about Build/Store frontends, it was more of an
explanation why we want WASM builds to be nice, it can be tracked in
separate TODOs once more concrete.

Change-Id: If4f5e0994b55520ba70cabefb4fcef9dc17bc394
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11945
Tested-by: BuildkiteCI
Reviewed-by: Ilan Joselevich <personal@ilanjoselevich.com>
Reviewed-by: flokli <flokli@flokli.de>
Autosubmit: flokli <flokli@flokli.de>

1 files changed, 6 insertions, 20 deletions

diff --git a/tvix/docs/src/TODO.md b/tvix/docs/src/TODO.md
index 52fa0a9e7480..fe161e3412d4 100644
--- a/tvix/docs/src/TODO.md
+++ b/tvix/docs/src/TODO.md
@@ -30,26 +30,12 @@ Most of Tvix is living inside a `//tvix` cargo workspace, and we use `crate2nix`
 as a build system, to get crate-level build granularity (and caching), keeping
 compile times somewhat manageable.
 
-In the future, for Store/Build, we want to build some more web frontends,
-exposing some data by calling to the API. Being able to write this in Rust,
-and reusing most of our existing code dealing with the data structures would
-be preferred.
-
-However, using the crate2nix tooling in combination with compiling for WASM is
-a bumpy ride (and `//web.tvixbolt` works around this by using
-`rustPlatform.buildRustPackage` instead, which invokes cargo inside a FOD):
-
-`buildRustCrate` in nixpkgs (which is used by `crate2nix` under the hood)
-doesn't allow specifying another `--target` explicitly, but relies on the cross
-machinery in nixpkgs exclusively.
-
-`doc/languages-frameworks/rust.section.md` suggests it should be a matter of
-re-instantiating nixpkgs for `wasm32-unknown-unknown`, but that's no recognized
-as a valid architecture.
-The suggested alternative, setting only `rustc.config` to it seems to get us
-further, but the `Crate.nix` logic for detecting arch-conditional crates doesn't
-seem to cover that case, and tries to build crates (`cpufeatures` for `sha{1,2}`)
-which are supposed to be skipped.
+Thanks to the recent crate2nix fixes, we can now use it to build WASM.
+We should migrate `//web/tvixbolt` from `rustPlatform.buildRustPackage` to
+`crate2nix`.
+An initial cl/11821 to move it to the `//tvix` workspace got some pushback, we
+should see if it's possible to keep it in a separate directory and still refer
+to the (cleaned) sources described in `tvix/default.nix`.
 
 ## Perf
  - String Contexts currently do a lot of indirections (edef)