Implement wasm proc-macros using wasmi#157709
Draft
bjorn3 wants to merge 6 commits into
Draft
Conversation
rustbot
added
A-meta
This comment has been minimized.
This comment has been minimized.
bjorn3
force-pushed
the
proc_macro_refactors5
branch
from
7f2358a to
3572b0e
Compare
rustbot
added
A-tidy
bjorn3
force-pushed
the
proc_macro_refactors5
branch
from
3572b0e to
3f33572
Compare
This comment has been minimized.
This comment has been minimized.
bjorn3
force-pushed
the
proc_macro_refactors5
branch
from
3f33572 to
3f346c6
Compare
bjorn3
force-pushed
the
proc_macro_refactors5
branch
2 times, most recently
from
45afede to
439c9eb
Compare
JonathanBrouwer
added a commit
to JonathanBrouwer/rust
that referenced
this pull request
Jun 22, 2026
…=Mark-Simulacrum Fix linking for wasm with crate metadata included On wasm the crate metadata ends up in a custom section. It is not possible to refer to create symbols inside a custom section, so attempting to export it during linking will result in a linker error. This keeps the target spec flag to deny compiling rust dylibs for wasm, but may theoretically allow compiling wasm rust dylibs with a custom target spec. It will help with wasm proc-macros. And in the future we can try to flip the only-cdylib option to false on wasm. Extracted out of rust-lang#157709, but also helps with rust-lang#157590. r? @Mark-Simulacrum
JonathanBrouwer
added a commit
to JonathanBrouwer/rust
that referenced
this pull request
Jun 22, 2026
…=Mark-Simulacrum Fix linking for wasm with crate metadata included On wasm the crate metadata ends up in a custom section. It is not possible to refer to create symbols inside a custom section, so attempting to export it during linking will result in a linker error. This keeps the target spec flag to deny compiling rust dylibs for wasm, but may theoretically allow compiling wasm rust dylibs with a custom target spec. It will help with wasm proc-macros. And in the future we can try to flip the only-cdylib option to false on wasm. Extracted out of rust-lang#157709, but also helps with rust-lang#157590. r? @Mark-Simulacrum
JonathanBrouwer
added a commit
to JonathanBrouwer/rust
that referenced
this pull request
Jun 22, 2026
…=Mark-Simulacrum Fix linking for wasm with crate metadata included On wasm the crate metadata ends up in a custom section. It is not possible to refer to create symbols inside a custom section, so attempting to export it during linking will result in a linker error. This keeps the target spec flag to deny compiling rust dylibs for wasm, but may theoretically allow compiling wasm rust dylibs with a custom target spec. It will help with wasm proc-macros. And in the future we can try to flip the only-cdylib option to false on wasm. Extracted out of rust-lang#157709, but also helps with rust-lang#157590. r? @Mark-Simulacrum
JonathanBrouwer
added a commit
to JonathanBrouwer/rust
that referenced
this pull request
Jun 22, 2026
…=Mark-Simulacrum Fix linking for wasm with crate metadata included On wasm the crate metadata ends up in a custom section. It is not possible to refer to create symbols inside a custom section, so attempting to export it during linking will result in a linker error. This keeps the target spec flag to deny compiling rust dylibs for wasm, but may theoretically allow compiling wasm rust dylibs with a custom target spec. It will help with wasm proc-macros. And in the future we can try to flip the only-cdylib option to false on wasm. Extracted out of rust-lang#157709, but also helps with rust-lang#157590. r? @Mark-Simulacrum
rust-timer
added a commit
that referenced
this pull request
Jun 22, 2026
Rollup merge of #158242 - bjorn3:wasm_rust_dylib_metadata, r=Mark-Simulacrum Fix linking for wasm with crate metadata included On wasm the crate metadata ends up in a custom section. It is not possible to refer to create symbols inside a custom section, so attempting to export it during linking will result in a linker error. This keeps the target spec flag to deny compiling rust dylibs for wasm, but may theoretically allow compiling wasm rust dylibs with a custom target spec. It will help with wasm proc-macros. And in the future we can try to flip the only-cdylib option to false on wasm. Extracted out of #157709, but also helps with #157590. r? @Mark-Simulacrum
bjorn3
force-pushed
the
proc_macro_refactors5
branch
from
439c9eb to
eadf95b
Compare
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
3 participants
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
This is an alternative approach to rust-lang/all-hands-2026#73. Unlike #157590 this uses wasmi + wasm32-wasip1. The advantage of this that it allows us to unconditionally depend on support for wasm proc-macros, allowing us to use them instead of the
-Zdual-proc-macrohack as well as using proc-macros in the standard library without breaking cross-compilation. And by removing the last commit this can even use wasm32-unknown-unknown to avoid depending on wasi-sdk (which currently has a bootstrap cycle with rustc and thus might not be a great dependency to have for building rustc as it makes the lives of distros harder)Once wasmtime supports all architectures for which we support host tools, swapping wasi for wasmtime is trivial. After that at a future point we can switch to the component model to allow using wasm32-wasip2 once we deem the advantages of this to outweigh the code duplication cost for the extra proc-macro ABI, extra code for handling the crate metadata for wasm components and the hack necessary to get wit-bindgen to work within the context of libproc_macro. This PR should not make this harder, while allowing us to get (some of) the benefits of wasm proc-macros earlier.
cc @Mark-Simulacrum @alexcrichton