Don't emit unexpected cfgs in proc-macros (#4284)

This changes when the `#[coverage]` attribute is emitted by adding an internal `coverage` crate feature to the proc-macro and their utility crates. This crate feature is enabled by `wasm-bindgen` and `wasm-bindgen-test` when `cfg(wasm_bindgen_unstable_test_coverage)` is enabled.

Author: daxpedda

.github/workflows/main.yml

@@ -67,12 +67,12 @@ jobs:
     - run: cargo clippy --no-deps --all-features -p example-tests -- -D warnings
     - run: cargo clippy --no-deps --all-features -p wasm-bindgen-externref-xform -- -D warnings
     - run: cargo clippy --no-deps --all-features --target wasm32-unknown-unknown -p wasm-bindgen-futures -- -D warnings
-    - run: cargo clippy --no-deps --all-features -p wasm-bindgen-macro -- -D warnings
-    - run: cargo clippy --no-deps --all-features -p wasm-bindgen-macro-support -- -D warnings
+    - run: cargo clippy --no-deps --features spans,strict-macro -p wasm-bindgen-macro -- -D warnings
+    - run: cargo clippy --no-deps --features extra-traits,spans,strict-macro -p wasm-bindgen-macro-support -- -D warnings
     - run: cargo clippy --no-deps --all-features -p wasm-bindgen-multi-value-xform -- -D warnings
     - run: cargo clippy --no-deps --all-features -p wasm-bindgen-shared -- -D warnings
     - run: cargo clippy --no-deps --all-features --target wasm32-unknown-unknown -p wasm-bindgen-test -- -D warnings
-    - run: cargo clippy --no-deps --all-features -p wasm-bindgen-test-macro -- -D warnings
+    - run: cargo clippy --no-deps -p wasm-bindgen-test-macro -- -D warnings
     - run: cargo clippy --no-deps --all-features -p wasm-bindgen-threads-xform -- -D warnings
     - run: cargo clippy --no-deps --all-features --target wasm32-unknown-unknown -p typescript-tests -- -D warnings
     - run: cargo clippy --no-deps --all-features -p wasm-bindgen-wasm-conventions -- -D warnings

Cargo.toml

@@ -52,6 +52,11 @@ wasm-bindgen-macro = { path = "crates/macro", version = "=0.2.95", default-featu
   "atomics",
 ] }
 
+[target.'cfg(all(target_arch = "wasm32", any(target_os = "unknown", target_os = "none"), wasm_bindgen_unstable_test_coverage))'.dependencies]
+wasm-bindgen-macro = { path = "crates/macro", version = "=0.2.95", default-features = false, features = [
+  "coverage",
+] }
+
 [dev-dependencies]
 wasm-bindgen-test = { path = 'crates/test' }
 

crates/backend/Cargo.toml

@@ -15,6 +15,7 @@ version = "0.2.95"
 
 [features]
 atomics = []
+coverage = []
 default = ["std"]
 extra-traits = ["syn/extra-traits"]
 spans = []

crates/backend/src/codegen.rs

@@ -224,6 +224,7 @@ impl ToTokens for ast::Struct {
         let free_fn = Ident::new(&shared::free_function(&name_str), Span::call_site());
         let unwrap_fn = Ident::new(&shared::unwrap_function(&name_str), Span::call_site());
         let wasm_bindgen = &self.wasm_bindgen;
+        let maybe_no_coverage = coverage();
         (quote! {
             #[automatically_derived]
             impl #wasm_bindgen::describe::WasmDescribe for #name {
@@ -300,7 +301,7 @@ impl ToTokens for ast::Struct {
                 #[doc(hidden)]
                 // `allow_delayed` is whether it's ok to not actually free the `ptr` immediately
                 // if it's still borrowed.
-                #[cfg_attr(wasm_bindgen_unstable_test_coverage, coverage(off))]
+                #maybe_no_coverage
                 pub unsafe extern "C" fn #free_fn(ptr: u32, allow_delayed: u32) {
                     use #wasm_bindgen::__rt::alloc::rc::Rc;
 
@@ -476,6 +477,7 @@ impl ToTokens for ast::StructField {
             quote! { assert_copy::<#ty>() }
         };
         let maybe_assert_copy = respan(maybe_assert_copy, ty);
+        let maybe_no_coverage = coverage();
 
         // Split this out so that it isn't affected by `quote_spanned!`.
         //
@@ -496,7 +498,7 @@ impl ToTokens for ast::StructField {
             const _: () = {
                 #[cfg_attr(all(target_arch = "wasm32", any(target_os = "unknown", target_os = "none")), no_mangle)]
                 #[doc(hidden)]
-                #[cfg_attr(wasm_bindgen_unstable_test_coverage, coverage(off))]
+                #maybe_no_coverage
                 pub unsafe extern "C" fn #getter(js: u32)
                     -> #wasm_bindgen::convert::WasmRet<<#ty as #wasm_bindgen::convert::IntoWasmAbi>::Abi>
                 {
@@ -538,7 +540,7 @@ impl ToTokens for ast::StructField {
             const _: () = {
                 #[no_mangle]
                 #[doc(hidden)]
-                #[cfg_attr(wasm_bindgen_unstable_test_coverage, coverage(off))]
+                #maybe_no_coverage
                 pub unsafe extern "C" fn #setter(
                     js: u32,
                     #(#args,)*
@@ -787,6 +789,8 @@ impl TryToTokens for ast::Export {
             quote! {}
         };
 
+        let maybe_no_coverage = coverage();
+
         (quote! {
             #[automatically_derived]
             const _: () = {
@@ -795,7 +799,7 @@ impl TryToTokens for ast::Export {
                     all(target_arch = "wasm32", any(target_os = "unknown", target_os = "none")),
                     export_name = #export_name,
                 )]
-                #[cfg_attr(wasm_bindgen_unstable_test_coverage, coverage(off))]
+                #maybe_no_coverage
                 pub unsafe extern "C" fn #generated_name(#(#args),*) -> #wasm_bindgen::convert::WasmRet<#projection::Abi> {
                     #start_check
 
@@ -1156,6 +1160,8 @@ impl ToTokens for ast::StringEnum {
         let hole = variant_count + 1;
         let attrs = &self.rust_attrs;
 
+        let maybe_no_coverage = coverage();
+
         let invalid_to_str_msg = format!(
             "Converting an invalid string enum ({}) back to a string is currently not supported",
             enum_name
@@ -1242,7 +1248,7 @@ impl ToTokens for ast::StringEnum {
 
             #[automatically_derived]
             impl #wasm_bindgen::describe::WasmDescribe for #enum_name {
-                #[cfg_attr(wasm_bindgen_unstable_test_coverage, coverage(off))]
+                #maybe_no_coverage
                 fn describe() {
                     use #wasm_bindgen::describe::*;
                     inform(STRING_ENUM);
@@ -1541,6 +1547,7 @@ impl ToTokens for ast::Enum {
         } else {
             quote! { u32 }
         };
+        let maybe_no_coverage = coverage();
         let cast_clauses = self.variants.iter().map(|variant| {
             let variant_name = &variant.name;
             quote! {
@@ -1588,7 +1595,7 @@ impl ToTokens for ast::Enum {
 
             #[automatically_derived]
             impl #wasm_bindgen::describe::WasmDescribe for #enum_name {
-                #[cfg_attr(wasm_bindgen_unstable_test_coverage, coverage(off))]
+                #maybe_no_coverage
                 fn describe() {
                     use #wasm_bindgen::describe::*;
                     inform(ENUM);
@@ -1853,6 +1860,8 @@ impl<'a, T: ToTokens> ToTokens for Descriptor<'a, T> {
             return;
         }
 
+        let maybe_no_coverage = coverage();
+
         let name = Ident::new(&format!("__wbindgen_describe_{}", ident), ident.span());
         let inner = &self.inner;
         let attrs = &self.attrs;
@@ -1864,7 +1873,7 @@ impl<'a, T: ToTokens> ToTokens for Descriptor<'a, T> {
                 #(#attrs)*
                 #[no_mangle]
                 #[doc(hidden)]
-                #[cfg_attr(wasm_bindgen_unstable_test_coverage, coverage(off))]
+                #maybe_no_coverage
                 pub extern "C" fn #name() {
                     use #wasm_bindgen::describe::*;
                     // See definition of `link_mem_intrinsics` for what this is doing
@@ -1955,3 +1964,10 @@ fn respan(input: TokenStream, span: &dyn ToTokens) -> TokenStream {
     }
     new_tokens.into_iter().collect()
 }
+
+fn coverage() -> Option<TokenStream> {
+    #[cfg(feature = "coverage")]
+    return Some(quote! { #[coverage(off)] });
+    #[cfg(not(feature = "coverage"))]
+    None
+}

crates/macro-support/Cargo.toml

@@ -15,6 +15,7 @@ version = "0.2.95"
 
 [features]
 atomics = ["wasm-bindgen-backend/atomics"]
+coverage = ["wasm-bindgen-backend/coverage"]
 default = ["std"]
 extra-traits = ["syn/extra-traits"]
 spans = ["wasm-bindgen-backend/spans"]

crates/macro/Cargo.toml

@@ -18,6 +18,7 @@ proc-macro = true
 
 [features]
 atomics = ["wasm-bindgen-macro-support/atomics"]
+coverage = ["wasm-bindgen-macro-support/coverage"]
 default = ["std"]
 spans = ["wasm-bindgen-macro-support/spans"]
 std = ["wasm-bindgen-macro-support/std"]
@@ -34,6 +35,3 @@ trybuild = "1.0"
 wasm-bindgen = { path = "../.." }
 wasm-bindgen-futures = { path = "../futures" }
 web-sys = { path = "../web-sys", features = ["Worker"] }
-
-[lints.rust]
-unexpected_cfgs = { level = "warn", check-cfg = ['cfg(wasm_bindgen_unstable_test_coverage)'] }

crates/macro/src/lib.rs

@@ -1,9 +1,6 @@
 #![doc(html_root_url = "https://docs.rs/wasm-bindgen-macro/0.2")]
 #![cfg_attr(
-    any(
-        wasm_bindgen_unstable_test_coverage,
-        all(not(feature = "std"), feature = "atomics")
-    ),
+    any(feature = "coverage", all(not(feature = "std"), feature = "atomics")),
     feature(allow_internal_unstable),
     allow(internal_features)
 )]
@@ -14,10 +11,7 @@ use proc_macro::TokenStream;
 use quote::quote;
 
 #[proc_macro_attribute]
-#[cfg_attr(
-    wasm_bindgen_unstable_test_coverage,
-    allow_internal_unstable(coverage_attribute)
-)]
+#[cfg_attr(feature = "coverage", allow_internal_unstable(coverage_attribute))]
 #[cfg_attr(
     all(not(feature = "std"), feature = "atomics"),
     allow_internal_unstable(thread_local)
@@ -48,10 +42,7 @@ pub fn wasm_bindgen(attr: TokenStream, input: TokenStream) -> TokenStream {
 /// let worker = Worker::new(&wasm_bindgen::link_to!(module = "/src/worker.js"));
 /// ```
 #[proc_macro]
-#[cfg_attr(
-    wasm_bindgen_unstable_test_coverage,
-    allow_internal_unstable(coverage_attribute)
-)]
+#[cfg_attr(feature = "coverage", allow_internal_unstable(coverage_attribute))]
 pub fn link_to(input: TokenStream) -> TokenStream {
     match wasm_bindgen_macro_support::expand_link_to(input.into()) {
         Ok(tokens) => {
@@ -68,10 +59,7 @@ pub fn link_to(input: TokenStream) -> TokenStream {
 }
 
 #[proc_macro_attribute]
-#[cfg_attr(
-    wasm_bindgen_unstable_test_coverage,
-    allow_internal_unstable(coverage_attribute)
-)]
+#[cfg_attr(feature = "coverage", allow_internal_unstable(coverage_attribute))]
 pub fn __wasm_bindgen_class_marker(attr: TokenStream, input: TokenStream) -> TokenStream {
     match wasm_bindgen_macro_support::expand_class_marker(attr.into(), input.into()) {
         Ok(tokens) => {

crates/test-macro/Cargo.toml

@@ -12,6 +12,9 @@ version = "0.3.45"
 [lib]
 proc-macro = true
 
+[features]
+coverage = []
+
 [dependencies]
 proc-macro2 = "1.0"
 quote = "1.0"
@@ -26,6 +29,3 @@ syn = { version = "2.0", default-features = false, features = [
 tokio = { version = "1", features = ["macros", "rt-multi-thread"] }
 trybuild = "1.0"
 wasm-bindgen-test = { path = "../test" }
-
-[lints.rust]
-unexpected_cfgs = { level = "warn", check-cfg = ['cfg(wasm_bindgen_unstable_test_coverage)'] }

crates/test-macro/src/lib.rs

@@ -2,7 +2,7 @@
 //! going on here.
 
 #![cfg_attr(
-    wasm_bindgen_unstable_test_coverage,
+    feature = "coverage",
     feature(allow_internal_unstable),
     allow(internal_features)
 )]
@@ -18,10 +18,7 @@ use std::sync::atomic::*;
 static CNT: AtomicUsize = AtomicUsize::new(0);
 
 #[proc_macro_attribute]
-#[cfg_attr(
-    wasm_bindgen_unstable_test_coverage,
-    allow_internal_unstable(coverage_attribute)
-)]
+#[cfg_attr(feature = "coverage", allow_internal_unstable(coverage_attribute))]
 pub fn wasm_bindgen_test(
     attr: proc_macro::TokenStream,
     body: proc_macro::TokenStream,
@@ -109,12 +106,17 @@ pub fn wasm_bindgen_test(
     // main test harness. This is the entry point for all tests.
     let name = format_ident!("__wbgt_{}_{}", ident, CNT.fetch_add(1, Ordering::SeqCst));
     let wasm_bindgen_path = attributes.wasm_bindgen_path;
+    let coverage = if cfg!(feature = "coverage") {
+        Some(quote! { #[coverage(off)] })
+    } else {
+        None
+    };
     tokens.extend(
         quote! {
             const _: () = {
                 #[no_mangle]
                 #[cfg(all(target_arch = "wasm32", any(target_os = "unknown", target_os = "none")))]
-                #[cfg_attr(wasm_bindgen_unstable_test_coverage, coverage(off))]
+                #coverage
                 pub extern "C" fn #name(cx: &#wasm_bindgen_path::__rt::Context) {
                     let test_name = ::core::concat!(::core::module_path!(), "::", ::core::stringify!(#ident));
                     #test_body

crates/test/Cargo.toml

@@ -24,6 +24,7 @@ wasm-bindgen-test-macro = { path = '../test-macro', version = '=0.3.45' }
 
 [target.'cfg(all(target_arch = "wasm32", wasm_bindgen_unstable_test_coverage))'.dependencies]
 minicov = "0.3"
+wasm-bindgen-test-macro = { path = '../test-macro', version = '=0.3.45', features = ["coverage"] }
 
 [lints.rust]
 unexpected_cfgs = { level = "warn", check-cfg = ['cfg(wasm_bindgen_unstable_test_coverage)'] }

guide/src/wasm-bindgen-test/coverage.md

@@ -9,12 +9,7 @@ You can ask the runner to generate coverage data from functions marked as `#[was
 
 ## Enabling the feature
 
-To enable this feature, you need to set `cfg(wasm_bindgen_unstable_test_coverage)` for `wasm-bindgen-test` and its dependencies.
-
-Currently it is particularly difficult to [deliver compile-line arguments to proc-macros when cross-compiling with Cargo][1]. To circumvent this [host-config] can be used.
-
-[1]: https://github.com/rust-lang/cargo/issues/4423
-[host-config]: https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#host-config
+To enable this feature, you need to enable `cfg(wasm_bindgen_unstable_test_coverage)`.
 
 ## Generating the data
 
@@ -26,18 +21,18 @@ Due to the current limitation of `llvm-cov`, we can't collect profiling symbols
 
 ### Arguments to the test runner
 
-The following environment variables can be used to control the coverage output when [executing the test runner][2]:
+The following environment variables can be used to control the coverage output when [executing the test runner][1]:
 
-- `WASM_BINDGEN_UNSTABLE_TEST_PROFRAW_OUT` to control the file name of the profraw or the directory in which it is placed
+- `WASM_BINDGEN_UNSTABLE_TEST_PROFRAW_OUT` to control the file name of the profraw or the directory in which it is placed. It might be necessary to provide the full path if e.g. running tests in a workspace.
 - `WASM_BINDGEN_UNSTABLE_TEST_PROFRAW_PREFIX` to add a custom prefix to the profraw files. This can be useful if you're running the tests automatically in succession.
 
-[2]: usage.html#appendix-using-wasm-bindgen-test-without-wasm-pack
+[1]: usage.html#appendix-using-wasm-bindgen-test-without-wasm-pack
 
 ### Target features
 
-This feature relies on the [minicov] crate, which provides a profiling runtime for WebAssembly. It in turn uses [cc] to compile the runtime to Wasm, which [currently doesn't support accounting for target feature][3]. Use e.g. `CFLAGS_wasm32_unknown_unknown="-matomics -mbulk-memory"` to account for that.
+This feature relies on the [minicov] crate, which provides a profiling runtime for WebAssembly. It in turn uses [cc] to compile the runtime to Wasm, which [currently doesn't support accounting for target feature][2]. Use e.g. `CFLAGS_wasm32_unknown_unknown="-matomics -mbulk-memory"` to account for that.
 
-[3]: https://github.com/rust-lang/cc-rs/issues/268
+[2]: https://github.com/rust-lang/cc-rs/issues/268
 [cc]: https://crates.io/crates/cc
 [minicov]: https://crates.io/crates/minicov
 
@@ -47,13 +42,10 @@ This adapts code taken from the [Rustc book], see that for more examples and gen
 
 ```sh
 # Run the tests:
-# - `CARGO_HOST_RUSTFLAGS` to pass the configuration to `wasm-bindgen-macro`.
-# - `-Ztarget-applies-to-host -Zhost-config` to enable `CARGO_HOST_RUSTFLAGS`.
-# - `--tests` to not run documentation tests, which is currently not supported.
-CARGO_HOST_RUSTFLAGS=--cfg=wasm_bindgen_unstable_test_coverage \
+# `--tests` to not run documentation tests, which is currently not supported.
 RUSTFLAGS="-Cinstrument-coverage -Zno-profiler-runtime --emit=llvm-ir --cfg=wasm_bindgen_unstable_test_coverage" \
 CARGO_TARGET_WASM32_UNKNOWN_UNKNOWN_RUNNER=wasm-bindgen-test-runner \
-cargo +nightly test -Ztarget-applies-to-host -Zhost-config --tests
+cargo +nightly test --tests
 # Compile to object files:
 # - Extract a list of compiled artifacts from Cargo and filter them with `jq`.
 # - Figure out the path to the LLVM IR file corresponding to an artifact.
@@ -62,9 +54,8 @@ crate_name=name_of_the_tested_crate_in_snake_case
 objects=()
 IFS=$'\n'
 for file in $(
-    CARGO_HOST_RUSTFLAGS=--cfg=wasm_bindgen_unstable_test_coverage \
     RUSTFLAGS="-Cinstrument-coverage -Zno-profiler-runtime --emit=llvm-ir --cfg=wasm_bindgen_unstable_test_coverage" \
-    cargo +nightly test -Ztarget-applies-to-host -Zhost-config --tests --no-run --message-format=json | \
+    cargo +nightly test --tests --no-run --message-format=json | \
     jq -r "select(.reason == \"compiler-artifact\") | (select(.target.kind == [\"test\"]) // select(.target.name == \"$crate_name\")) | .filenames[0]"
 )
 do
@@ -89,7 +80,7 @@ llvm-cov-19 show -show-instantiations=false -Xdemangler=rustfilt -output-dir cov
 
 ## Attribution
 
-These methods have originally been pioneered by [Hacken OÜ], see [their guide][4] as well.
+These methods have originally been pioneered by [Hacken OÜ], see [their guide][3] as well.
 
-[4]: https://hknio.github.io/wasmcov
+[3]: https://hknio.github.io/wasmcov
 [Hacken OÜ]: https://hacken.io