Add -Zwasm-proc-macros flag by Mark-Simulacrum · Pull Request #160854 · rust-lang/rust

Mark-Simulacrum · 2026-08-10T12:32:22Z

This is currently not really implemented, but partial support for it is added in various places across the tree. This is a patch extracted from the wider set of work to make review easier, which wires up:

Unstable flag in rustc
Bootstrap flag to enable using wasm-proc-macros (this needs an extra std compilation, wiring into compiletest)
Partial compiletest support for the flag (mostly just CLI side of things)
- I suspect this will not work across all platforms but based on success with the full patch it should be enough for Linux, I think. I'd rather get them working on at least one platform and then iterate from there, unless we have clear ideas for improvements now.

cc #160389 (tracking issue)
cc #157590 (more complete implementation)

r? @bjorn3

rustbot · 2026-08-10T12:47:32Z

Some changes occurred in src/tools/compiletest

cc @jieyouxu

compiletest directives have been modified. Please add or update docs for the
new or modified directive in src/doc/rustc-dev-guide/.

This PR modifies src/bootstrap/src/core/config.

If appropriate, please update CONFIG_CHANGE_HISTORY in src/bootstrap/src/utils/change_tracker.rs.

This PR modifies bootstrap.example.toml.

If appropriate, please update CONFIG_CHANGE_HISTORY in src/bootstrap/src/utils/change_tracker.rs.

bjorn3 · 2026-08-10T13:04:06Z

+#
+# The implementation for this has not finished landing, so you probably don't
+# want to enable this right now.
+#rust.wasm-proc-macro = false


Maybe use plural macros here?

View changes since the review

Hm, do you think we should do the same for the -Z flag? I feel like it's nice for those to be consistent. I don't have a super strong opinion here either way though.

The flag already uses plural, right?

Oh, so it does. I didn't realize :) I guess the compiletest flag must be what I remembered.

I'll go ahead and rename to plural form everywhere then.

Or you remembered the PR title, as that incorrectly has the flag as singular.

bjorn3 · 2026-08-10T13:06:53Z

+                //
+                // wasm32-wasip2 should in principle always be able to link with wasm-component-ld +
+                // wasm-ld. This does mean that rust.lld needs to be enabled to build wasm-ld wrapper
+                // around rust-lld.


@jieyouxu do you know if there is a better way to force usage of the default linker or at least use the linker set for the wasm32-wasip2 target rather than the target that gets tested?

View changes since the review

Hm, I'm afraid I don't recall existing mechanisms to force reusing the "host" linker for the target-being-tested (cross-compile in compiletest was always a bit fishy)

Tracking the general problem in #160917.

This is currently not really implemented, but partial support for it is added in various places across the tree. This is a patch extracted from the wider set of work to make review easier, which wires up: * Unstable flag in rustc * Bootstrap flag to enable using wasm-proc-macros (this needs an extra std compilation, wiring into compiletest) * Partial compiletest support for the flag (mostly just CLI side of things)

rustbot · 2026-08-11T12:53:40Z

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

bjorn3 · 2026-08-11T12:58:32Z

+    if is_proc_macro_crate && sess.target.is_like_wasm && !sess.opts.unstable_opts.wasm_proc_macros
+    {
+        sess.dcx().emit_err(diagnostics::UnstableWasmProcMacro);
+    }


Doesn't have to be in this PR, but we should suppress the panic=abort warning below for wasm proc-macros.

View changes since the review

Yeah, I intentionally left that out to keep this more minimal and not really changing behavior (just plumbing).

bjorn3

r=me if @jieyouxu agrees with the compiletest changes

View changes since this review

jieyouxu

This is reasonable to get us started; the compiletest problem is more general (AFAIK the dual under-test toolchain is its own rabbit hole; tracking in #160917) and isn't worth blocking this over.

View changes since this review

bjorn3 · 2026-08-11T15:13:52Z

@bors r=bjorn3,jieyouxu

rust-bors · 2026-08-11T15:13:56Z

📌 Commit 6408d38 has been approved by bjorn3,jieyouxu

It is now in the queue for this repository.

@bjorn3

…, r=bjorn3,jieyouxu Add -Zwasm-proc-macros flag This is currently not really implemented, but partial support for it is added in various places across the tree. This is a patch extracted from the wider set of work to make review easier, which wires up: * Unstable flag in rustc * Bootstrap flag to enable using wasm-proc-macros (this needs an extra std compilation, wiring into compiletest) * Partial compiletest support for the flag (mostly just CLI side of things) * I suspect this will not work across all platforms but based on success with the full patch it should be enough for Linux, I think. I'd rather get them working on at least one platform and then iterate from there, unless we have clear ideas for improvements now. cc rust-lang#160389 (tracking issue) cc rust-lang#157590 (more complete implementation) r? @bjorn3

…uwer Rollup of 10 pull requests Successful merges: - #160620 (Do not pass `-no-pie` on Windows) - #160731 (Arc: Remove unnecessary fmt::Display use for overflow assertion) - #160760 (Miri: give the incremental session a chance to finish) - #160854 (Add -Zwasm-proc-macros flag) - #160868 (std: Adjust cfgs again for TLS on WASI) - #160894 (Allow running an arbitrary number of try jobs per PR) - #160790 (rustc-book: update sys-v abi link) - #160878 (Add rust_analyzer to check-cfg names) - #160909 (tests/run-make-cargo/thumb-none-cortex-m: bump `cortex-m` dependency) - #160920 (No longer mention the removed generic)

@bjorn3

…, r=bjorn3,jieyouxu Add -Zwasm-proc-macros flag This is currently not really implemented, but partial support for it is added in various places across the tree. This is a patch extracted from the wider set of work to make review easier, which wires up: * Unstable flag in rustc * Bootstrap flag to enable using wasm-proc-macros (this needs an extra std compilation, wiring into compiletest) * Partial compiletest support for the flag (mostly just CLI side of things) * I suspect this will not work across all platforms but based on success with the full patch it should be enough for Linux, I think. I'd rather get them working on at least one platform and then iterate from there, unless we have clear ideas for improvements now. cc rust-lang#160389 (tracking issue) cc rust-lang#157590 (more complete implementation) r? @bjorn3

@bjorn3

…, r=bjorn3,jieyouxu Add -Zwasm-proc-macros flag This is currently not really implemented, but partial support for it is added in various places across the tree. This is a patch extracted from the wider set of work to make review easier, which wires up: * Unstable flag in rustc * Bootstrap flag to enable using wasm-proc-macros (this needs an extra std compilation, wiring into compiletest) * Partial compiletest support for the flag (mostly just CLI side of things) * I suspect this will not work across all platforms but based on success with the full patch it should be enough for Linux, I think. I'd rather get them working on at least one platform and then iterate from there, unless we have clear ideas for improvements now. cc rust-lang#160389 (tracking issue) cc rust-lang#157590 (more complete implementation) r? @bjorn3

…uwer Rollup of 14 pull requests Successful merges: - #160620 (Do not pass `-no-pie` on Windows) - #160731 (Arc: Remove unnecessary fmt::Display use for overflow assertion) - #160760 (Miri: give the incremental session a chance to finish) - #160854 (Add -Zwasm-proc-macros flag) - #160868 (std: Adjust cfgs again for TLS on WASI) - #160894 (Allow running an arbitrary number of try jobs per PR) - #160790 (rustc-book: update sys-v abi link) - #160878 (Add rust_analyzer to check-cfg names) - #160909 (tests/run-make-cargo/thumb-none-cortex-m: bump `cortex-m` dependency) - #160920 (No longer mention the removed generic) - #160921 (rustdoc: Fix invalid CSS classes generated for notable items) - #160924 (split up `rustc_session`) - #160934 (Ensure TLS accesses don't call the global allocator through panic) - #160937 (Store the names of `Fn` trait parameters in the AST, fix rustfmt bug)

@bjorn3

…, r=bjorn3,jieyouxu Add -Zwasm-proc-macros flag This is currently not really implemented, but partial support for it is added in various places across the tree. This is a patch extracted from the wider set of work to make review easier, which wires up: * Unstable flag in rustc * Bootstrap flag to enable using wasm-proc-macros (this needs an extra std compilation, wiring into compiletest) * Partial compiletest support for the flag (mostly just CLI side of things) * I suspect this will not work across all platforms but based on success with the full patch it should be enough for Linux, I think. I'd rather get them working on at least one platform and then iterate from there, unless we have clear ideas for improvements now. cc rust-lang#160389 (tracking issue) cc rust-lang#157590 (more complete implementation) r? @bjorn3

rustbot assigned bjorn3 Aug 10, 2026

Mark-Simulacrum marked this pull request as ready for review August 10, 2026 12:47

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Aug 10, 2026

bjorn3 reviewed Aug 10, 2026

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Mark-Simulacrum changed the title ~~Add -Zwasm-proc-macro flag~~ Add -Zwasm-proc-macrso flag Aug 11, 2026

Mark-Simulacrum changed the title ~~Add -Zwasm-proc-macrso flag~~ Add -Zwasm-proc-macros flag Aug 11, 2026

Mark-Simulacrum force-pushed the wasm-macro-partial branch from 9154741 to 6408d38 Compare August 11, 2026 12:53

bjorn3 reviewed Aug 11, 2026

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bjorn3 approved these changes Aug 11, 2026

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jieyouxu approved these changes Aug 11, 2026

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rust-bors Bot added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Aug 11, 2026

JonathanBrouwer mentioned this pull request Aug 11, 2026

Rollup of 10 pull requests #160929

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JonathanBrouwer mentioned this pull request Aug 11, 2026

Rollup of 15 pull requests #160947

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JonathanBrouwer mentioned this pull request Aug 11, 2026

Rollup of 14 pull requests #160948

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jhpratt mentioned this pull request Aug 12, 2026

Rollup of 14 pull requests #160954

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