ci: cleanup & reproducibility

.github/workflows/ci.yml

@@ -14,7 +14,6 @@ jobs:
         os: [ubuntu-latest, macOS-latest]
     steps:
       - uses: actions/checkout@v6
-      - uses: dtolnay/rust-toolchain@stable
       - run: cargo check
 
   test:
@@ -25,7 +24,6 @@ jobs:
         os: [ubuntu-latest, macOS-latest]
     steps:
       - uses: actions/checkout@v6
-      - uses: dtolnay/rust-toolchain@stable
       - run: cargo test
 
   fmt:
@@ -33,8 +31,6 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v6
-      - uses: dtolnay/rust-toolchain@stable
-      - run: rustup component add rustfmt
       - run: cargo fmt --all -- --check
 
   clippy:
@@ -45,8 +41,6 @@ jobs:
         os: [ubuntu-latest, macOS-latest]
     steps:
       - uses: actions/checkout@v6
-      - uses: dtolnay/rust-toolchain@stable
-      - run: rustup component add clippy
       - run: cargo clippy -- -D warnings
 
   coverage:
@@ -67,7 +61,7 @@ jobs:
         ## VARs setup
         outputs() { step_id="vars"; for var in "$@" ; do echo steps.${step_id}.outputs.${var}="${!var}"; echo "${var}=${!var}" >> $GITHUB_OUTPUT; done; }
         # toolchain
-        TOOLCHAIN="nightly" ## default to "nightly" toolchain (required for certain required unstable compiler flags) ## !maint: refactor when stable channel has needed support
+        echo "RUSTC_BOOTSTRAP=1" >> "${GITHUB_ENV}"
         # * use requested TOOLCHAIN if specified
         if [ -n "${{ matrix.job.toolchain }}" ]; then TOOLCHAIN="${{ matrix.job.toolchain }}" ; fi
         outputs TOOLCHAIN
@@ -77,7 +71,7 @@ jobs:
         outputs CODECOV_FLAGS
 
     - name: rust toolchain ~ install
-      uses: dtolnay/rust-toolchain@nightly
+      uses: dtolnay/rust-toolchain@stable
       with:
         components: llvm-tools-preview
     - name: Test
@@ -92,12 +86,12 @@ jobs:
       id: build_grcov
       shell: bash
       run: |
-        git clone https://github.com/mozilla/grcov.git ~/grcov/
+        git clone --depth=1 https://github.com/mozilla/grcov.git ~/grcov/
         cd ~/grcov
         # Hardcode the version of crossbeam-epoch. See
         # https://github.com/uutils/coreutils/issues/3680
         sed -i -e "s|tempfile =|crossbeam-epoch = \"=0.9.8\"\ntempfile =|" Cargo.toml
-        cargo install --path .
+        cargo install --path . --locked
         cd -
 # Uncomment when the upstream issue
 # https://github.com/mozilla/grcov/issues/849 is fixed