chore: Don't consider test code “code under test”

changelog: ignore

Author: jan-ferdinand

.github/workflows/coverage.yml

@@ -16,8 +16,8 @@ jobs:
       - name: Checkout repository
         uses: actions/checkout@v4
 
-      - name: Install stable toolchain
-        uses: dtolnay/rust-toolchain@stable
+      - name: Install nightly toolchain
+        uses: dtolnay/rust-toolchain@nightly
         with:
           components: llvm-tools-preview
 
@@ -28,7 +28,7 @@ jobs:
         uses: taiki-e/install-action@nextest
 
       - name: Collect coverage data
-        run: cargo llvm-cov nextest --all-targets --lcov --output-path lcov.info
+        run: cargo +nightly llvm-cov nextest --all-targets --lcov --output-path lcov.info
 
       - name: Upload coverage to coveralls.io
         uses: coverallsapp/github-action@v2

Cargo.toml

@@ -15,5 +15,8 @@ readme = "README.md"
 
 [workspace.lints]
 
+[workspace.lints.rust]
+unexpected_cfgs = { level = "warn", check-cfg = ['cfg(coverage_nightly)'] }
+
 [profile.release]
 lto = "thin"

bfieldcodec_derive/src/lib.rs

@@ -1173,6 +1173,7 @@ impl BFieldCodecErrorEnumBuilder {
 }
 
 #[cfg(test)]
+#[cfg_attr(coverage_nightly, coverage(off))]
 mod tests {
     use syn::parse_quote;
 

twenty-first/src/lib.rs

@@ -1,4 +1,18 @@
 #![deny(clippy::shadow_unrelated)]
+//
+// If code coverage tool `cargo-llvm-cov` is running with the nightly toolchain,
+// enable the unstable “coverage” attribute. This allows using the annotation
+// `#[coverage(off)]` to explicitly exclude certain parts of the code from
+// being considered as “code under test.” Most prominently, the annotation
+// should be added to every `#[cfg(test)]` module. Since the “coverage”
+// feature is enable only conditionally, the annotation to use is:
+// #[cfg_attr(coverage_nightly, coverage(off))]
+//
+// See also:
+// - https://github.com/taiki-e/cargo-llvm-cov#exclude-code-from-coverage
+// - https://github.com/rust-lang/rust/issues/84605
+#![cfg_attr(coverage_nightly, feature(coverage_attribute))]
+
 pub mod config;
 pub mod error;
 pub mod math;
@@ -20,6 +34,7 @@ extern crate self as twenty_first;
 pub use bfieldcodec_derive;
 
 #[cfg(test)]
+#[cfg_attr(coverage_nightly, coverage(off))]
 pub(crate) mod tests {
     use prelude::*;
 

twenty-first/src/math/b_field_element.rs

@@ -793,7 +793,8 @@ impl PrimitiveRootOfUnity for BFieldElement {
 }
 
 #[cfg(test)]
-mod b_prime_field_element_test {
+#[cfg_attr(coverage_nightly, coverage(off))]
+mod tests {
     use std::collections::hash_map::DefaultHasher;
     use std::hash::Hasher;
 

twenty-first/src/math/bfield_codec.rs

@@ -593,6 +593,7 @@ impl<T> BFieldCodec for PhantomData<T> {
 }
 
 #[cfg(test)]
+#[cfg_attr(coverage_nightly, coverage(off))]
 mod tests {
     use num_traits::ConstZero;
     use num_traits::Zero;
@@ -894,8 +895,7 @@ mod tests {
     /// See also: https://github.com/rust-lang/cargo/issues/8379#issuecomment-1261970561
     ///
     /// [^1]: almost-cyclic because the dependency would be a dev-dependency
-    #[cfg(test)]
-    pub mod derive_tests {
+    pub mod derive {
         use arbitrary::Arbitrary;
         use num_traits::Zero;
 

twenty-first/src/math/lattice.rs

@@ -813,7 +813,8 @@ pub mod kem {
     }
 
     #[cfg(test)]
-    mod test {
+    #[cfg_attr(coverage_nightly, coverage(off))]
+    mod tests {
         use super::*;
 
         #[test]
@@ -832,7 +833,8 @@ pub mod kem {
 }
 
 #[cfg(test)]
-mod lattice_test {
+#[cfg_attr(coverage_nightly, coverage(off))]
+mod tests {
     use itertools::Itertools;
     use num_traits::ConstOne;
     use num_traits::Zero;

twenty-first/src/math/ntt.rs

@@ -307,6 +307,7 @@ pub fn twiddle_factors(slice_len: u32, root_of_unity: BFieldElement) -> Vec<Vec<
 }
 
 #[cfg(test)]
+#[cfg_attr(coverage_nightly, coverage(off))]
 mod tests {
     use itertools::Itertools;
     use num_traits::ConstZero;

twenty-first/src/math/polynomial.rs

@@ -2701,7 +2701,8 @@ where
 }
 
 #[cfg(test)]
-mod test_polynomials {
+#[cfg_attr(coverage_nightly, coverage(off))]
+mod tests {
     use num_traits::ConstZero;
     use proptest::collection::size_range;
     use proptest::collection::vec;

twenty-first/src/math/x_field_element.rs

@@ -658,6 +658,7 @@ impl ModPowU32 for XFieldElement {
 }
 
 #[cfg(test)]
+#[cfg_attr(coverage_nightly, coverage(off))]
 mod tests {
     use itertools::Itertools;
     use itertools::izip;