sha2: replace soft crate feature with configuration flag (#615)

To force use of the software backend users now have to use
`RUSTFLAGS='--cfg sha2_backend="soft"'`.

.github/workflows/sha2.yml

@@ -14,7 +14,7 @@ defaults:
     working-directory: sha2
 
 env:
-  RUSTFLAGS: "-Dwarnings"
+  RUSTFLAGS: -Dwarnings
   CARGO_INCREMENTAL: 0
 
 jobs:
@@ -76,6 +76,9 @@ jobs:
       - uses: RustCrypto/actions/cargo-hack-install@master
       - run: ${{ matrix.deps }}
       - run: cargo hack test --feature-powerset
+      - run: cargo test --all-features
+        env:
+          RUSTFLAGS: -Dwarnings --cfg sha2_backend="soft"
 
   # macOS tests
   macos:
@@ -93,10 +96,12 @@ jobs:
         with:
           toolchain: ${{ matrix.rust }}
           targets: x86_64-apple-darwin
-      - uses: RustCrypto/actions/cargo-hack-install@master
       - run: cargo test --no-default-features
       - run: cargo test
       - run: cargo test --all-features
+      - run: cargo test --all-features
+        env:
+          RUSTFLAGS: -Dwarnings --cfg sha2_backend="soft"
 
   # Windows tests
   windows:
@@ -118,6 +123,9 @@ jobs:
           targets: ${{ matrix.target }}
       - uses: msys2/setup-msys2@v2
       - run: cargo test --target ${{ matrix.target }}
+      - run: cargo test --all-features
+        env:
+          RUSTFLAGS: -Dwarnings --cfg sha2_backend="soft"
 
   # Cross-compiled tests
   cross:
@@ -159,12 +167,15 @@ jobs:
         with:
           toolchain: nightly
       - run: cargo install cross --git https://github.com/cross-rs/cross
-      - run: cross test --package sha2 --target riscv64gc-unknown-linux-gnu
+      - run: cross test --package sha2 --all-features --target riscv64gc-unknown-linux-gnu
         env:
-          RUSTFLAGS: '-Dwarnings --cfg sha2_backend="riscv-zknh" -C target-feature=+zknh'
-      - run: cross test --package sha2 --target riscv64gc-unknown-linux-gnu
+          RUSTFLAGS: -Dwarnings --cfg sha2_backend="soft" -C target-feature=+zknh
+      - run: cross test --package sha2 --all-features --target riscv64gc-unknown-linux-gnu
         env:
-          RUSTFLAGS: '-Dwarnings --cfg sha2_backend="riscv-zknh-compact" -C target-feature=+zknh'
+          RUSTFLAGS: -Dwarnings --cfg sha2_backend="riscv-zknh" -C target-feature=+zknh
+      - run: cross test --package sha2 --all-features --target riscv64gc-unknown-linux-gnu
+        env:
+          RUSTFLAGS: -Dwarnings --cfg sha2_backend="riscv-zknh-compact" -C target-feature=+zknh
 
   riscv32-zknh:
     runs-on: ubuntu-latest
@@ -175,12 +186,15 @@ jobs:
         with:
           toolchain: nightly
           components: rust-src
-      - run: cargo build --target riscv32gc-unknown-linux-gnu -Z build-std
+      - run: cargo build --all-features --target riscv32gc-unknown-linux-gnu -Z build-std
+        env:
+          RUSTFLAGS: -Dwarnings --cfg sha2_backend="soft" -C target-feature=+zknh
+      - run: cargo build --all-features --target riscv32gc-unknown-linux-gnu -Z build-std
         env:
-          RUSTFLAGS: '-Dwarnings --cfg sha2_backend="riscv-zknh" -C target-feature=+zknh'
-      - run: cargo build --target riscv32gc-unknown-linux-gnu -Z build-std
+          RUSTFLAGS: -Dwarnings --cfg sha2_backend="riscv-zknh" -C target-feature=+zknh
+      - run: cargo build --all-features --target riscv32gc-unknown-linux-gnu -Z build-std
         env:
-          RUSTFLAGS: '-Dwarnings --cfg sha2_backend="riscv-zknh-compact" -C target-feature=+zknh'
+          RUSTFLAGS: -Dwarnings --cfg sha2_backend="riscv-zknh-compact" -C target-feature=+zknh
 
   minimal-versions:
     uses: RustCrypto/actions/.github/workflows/minimal-versions.yml@master

sha2/CHANGELOG.md

@@ -6,10 +6,17 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## UNRELEASED
+### Added
+- RISC-V scalar crypto extension support gated behind `sha2_backend = "riscv-zknh"` or
+  `sha2_backend = "riscv-zknh-compact"` configuration flags [#614]
+
 ### Removed
 - `asm`, `asm-aarch64`, `loongarch64_asm`, and `compress` crate features [#542]
+- `soft` crate feature. Replaced with `sha2_backend = "soft"` configuration flag [#615]
 
 [#542]: https://github.com/RustCrypto/hashes/pull/542
+[#614]: https://github.com/RustCrypto/hashes/pull/614
+[#615]: https://github.com/RustCrypto/hashes/pull/615
 
 ## 0.10.8 (2023-09-26)
 ### Added

sha2/Cargo.toml

@@ -30,13 +30,14 @@ base16ct = { version = "0.2", features = ["alloc"] }
 [features]
 default = ["oid", "std"]
 std = ["digest/std"]
-oid = ["digest/oid"]         # Enable OID support
 zeroize = ["digest/zeroize"]
-force-soft = []              # Force software implementation
+oid = ["digest/oid"]
 
 [lints.rust.unexpected_cfgs]
 level = "warn"
-check-cfg = ['cfg(sha2_backend, values("riscv-zknh", "riscv-zknh-compact"))']
+check-cfg = [
+    'cfg(sha2_backend, values("soft", "riscv-zknh", "riscv-zknh-compact"))',
+]
 
 [package.metadata.docs.rs]
 all-features = true

sha2/src/sha256.rs

@@ -1,11 +1,11 @@
 cfg_if::cfg_if! {
-    if #[cfg(feature = "force-soft")] {
+    if #[cfg(sha2_backend = "soft")] {
         mod soft;
         use soft::compress;
     } else if #[cfg(any(target_arch = "x86", target_arch = "x86_64"))] {
         mod soft;
-        mod x86;
-        use x86::compress;
+        mod x86_shani;
+        use x86_shani::compress;
     } else if #[cfg(all(
         any(target_arch = "riscv32", target_arch = "riscv64"),
         sha2_backend = "riscv-zknh"

sha2/src/sha512.rs

@@ -1,11 +1,11 @@
 cfg_if::cfg_if! {
-    if #[cfg(feature = "force-soft")] {
+    if #[cfg(sha2_backend = "soft")] {
         mod soft;
         use soft::compress;
     } else if #[cfg(any(target_arch = "x86", target_arch = "x86_64"))] {
         mod soft;
-        mod x86;
-        use x86::compress;
+        mod x86_avx2;
+        use x86_avx2::compress;
     } else if #[cfg(all(
         any(target_arch = "riscv32", target_arch = "riscv64"),
         sha2_backend = "riscv-zknh"