Use preinstalled rust & stop incremental build

.github/workflows/ci.yml

@@ -11,30 +11,32 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        os: [ubuntu-latest, macOS-latest, windows-latest]
+        os: [ubuntu-latest, macos-latest, windows-latest]
+    env:
+      CARGO_INCREMENTAL: 0
     steps:
       - uses: actions/checkout@v6
-      - uses: dtolnay/rust-toolchain@stable
       - run: cargo check
 
   test:
     name: cargo test
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        os: [ubuntu-latest, macOS-latest, windows-latest]
+        os: [ubuntu-latest, macos-latest, windows-latest]
+    env:
+      CARGO_INCREMENTAL: 0
     steps:
       - uses: actions/checkout@v6
-      - uses: dtolnay/rust-toolchain@stable
       - run: cargo test --all
 
   fmt:
     name: cargo fmt --all -- --check
     runs-on: ubuntu-latest
+    env:
+      CARGO_INCREMENTAL: 0
     steps:
       - uses: actions/checkout@v6
-      - uses: dtolnay/rust-toolchain@stable
-      - run: rustup component add rustfmt
       - run: cargo fmt --all -- --check
 
   coverage:
@@ -47,6 +49,10 @@ jobs:
           - { os: ubuntu-latest  , features: unix }
           - { os: macos-latest   , features: macos }
           - { os: windows-latest , features: windows }
+    env:
+      CARGO_INCREMENTAL: 0
+      # Use -Z
+      RUSTC_BOOTSTRAP: 1
     steps:
     - uses: actions/checkout@v6
     - name: Initialize workflow variables
@@ -55,22 +61,10 @@ jobs:
       run: |
         ## 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
-        # * specify gnu-type TOOLCHAIN for windows; `grcov` requires gnu-style code coverage data files
-        case ${{ matrix.job.os }} in windows-*) TOOLCHAIN="$TOOLCHAIN-x86_64-pc-windows-gnu" ;; esac;
-        # * use requested TOOLCHAIN if specified
-        if [ -n "${{ matrix.job.toolchain }}" ]; then TOOLCHAIN="${{ matrix.job.toolchain }}" ; fi
-        outputs TOOLCHAIN
         # target-specific options
         # * CODECOV_FLAGS
         CODECOV_FLAGS=$( echo "${{ matrix.job.os }}" | sed 's/[^[:alnum:]]/_/g' )
         outputs CODECOV_FLAGS
-
-    - name: rust toolchain ~ install
-      uses: dtolnay/rust-toolchain@nightly
-      with:
-        components: llvm-tools-preview
     - name: Test
       run: cargo test --no-fail-fast
       env:
@@ -79,7 +73,13 @@ jobs:
         RUSTFLAGS: "-Cinstrument-coverage -Zcoverage-options=branch -Ccodegen-units=1 -Copt-level=0 -Coverflow-checks=off -Zpanic_abort_tests -Cpanic=abort"
         RUSTDOCFLAGS: "-Cpanic=abort"
         LLVM_PROFILE_FILE: "sed-%p-%m.profraw"
+        # Use -Z
+        RUSTC_BOOTSTRAP: 1
     - name: "`grcov` ~ install"
+      env:
+        CARGO_INCREMENTAL: 0
+        # Use -Z
+        RUSTC_BOOTSTRAP: 1
       id: build_grcov
       shell: bash
       run: |
@@ -98,6 +98,10 @@ jobs:
 #        version: latest
 #        use-tool-cache: false
     - name: Generate coverage data (via `grcov`)
+      env:
+        CARGO_INCREMENTAL: 0
+        # Use -Z
+        RUSTC_BOOTSTRAP: 1
       id: coverage
       shell: bash
       run: |

.github/workflows/code-quality.yml

@@ -24,17 +24,15 @@ jobs:
   style_format:
     name: Style/format
     runs-on: ${{ matrix.job.os }}
+    env:
+      CARGO_INCREMENTAL: 0
     strategy:
       fail-fast: false
       matrix:
         job:
           - { os: ubuntu-latest, features: feat_os_unix }
     steps:
       - uses: actions/checkout@v6
-      - uses: dtolnay/rust-toolchain@master
-        with:
-          toolchain: stable
-          components: rustfmt
       - uses: Swatinem/rust-cache@v2
       - name: Initialize workflow variables
         id: vars
@@ -65,6 +63,7 @@ jobs:
     env:
       SCCACHE_GHA_ENABLED: "true"
       RUSTC_WRAPPER: "sccache"
+      CARGO_INCREMENTAL: 0
     strategy:
       fail-fast: false
       matrix:
@@ -74,10 +73,6 @@ jobs:
           - { os: windows-latest }
     steps:
       - uses: actions/checkout@v6
-      - uses: dtolnay/rust-toolchain@master
-        with:
-          toolchain: stable
-          components: clippy
       - uses: Swatinem/rust-cache@v2
       - name: Run sccache-cache
         uses: mozilla-actions/sccache-action@v0.0.9