ci: Switch to a single matrix for build channels (verify_build)

The Mac, Windows, and Linux jobs for build channels are pretty
redundant. Turn this into a single `verify_build` job that has both OS
and version in its matrix. For consistency, rename the script to
`verify-build`.

To simplify variables, allow the build script to detect the OS rather
than passing it from CI.

.github/workflows/ci.yaml

@@ -1,4 +1,4 @@
-name: full CI
+name: CI
 
 on:
   merge_group:
@@ -9,6 +9,10 @@ env:
   CARGO_TERM_VERBOSE: true
   LIBC_CI: 1
 
+defaults:
+  run:
+    shell: bash
+
 jobs:
   style_check:
     name: Style check
@@ -20,71 +24,22 @@ jobs:
       - name: Check style
         run: ./ci/style.sh
 
-  build_channels_linux:
-    name: Build Channels Linux
-    runs-on: ubuntu-22.04
+  # This runs `cargo build --target ...` for all T1 and T2 targets`
+  verify_build:
+    name: Verify build
     strategy:
-      fail-fast: true
-      max-parallel: 5
       matrix:
-        toolchain:
-          - stable
-          - beta
-          - nightly
-          - 1.63.0
-    env:
-      OS: linux
-      TOOLCHAIN: ${{ matrix.toolchain }}
-    steps:
-      - uses: actions/checkout@v4
-      - name: Setup Rust toolchain
-        run: ./ci/install-rust.sh
-      - name: Execute build.sh
-        run: ./ci/build.sh
-
-  build_channels_macos:
-    name: Build Channels macOS
-    needs: macos
-    strategy:
-      fail-fast: true
-      max-parallel: 4
-      matrix:
-        target:
-          - { toolchain: stable, os: macos-14 }
-          - { toolchain: beta, os: macos-14 }
-          - { toolchain: nightly, os: macos-14 }
-          - { toolchain: 1.63.0, os: macos-14 }
-    runs-on: ${{ matrix.target.os }}
+        toolchain: [stable, nightly, 1.63.0, beta]
+        os: [ubuntu-22.04, macos-14, windows-2022]
+    runs-on: ${{ matrix.os }}
     env:
-      OS: macos
       TOOLCHAIN: ${{ matrix.toolchain }}
     steps:
       - uses: actions/checkout@v4
       - name: Setup Rust toolchain
         run: ./ci/install-rust.sh
       - name: Execute build.sh
-        run: ./ci/build.sh
-
-  build_channels_windows:
-    name: Build Channels Windows
-    runs-on: windows-2022
-    strategy:
-      fail-fast: true
-      matrix:
-        toolchain:
-          - 1.63.0
-          - stable
-    env:
-      OS: windows
-      TOOLCHAIN: ${{ matrix.toolchain }}
-    steps:
-      - uses: actions/checkout@v4
-      - name: Self-update rustup
-        run: rustup self update
-        shell: bash
-      - name: Execute build.sh
-        run: ./ci/build.sh
-        shell: bash
+        run: ./ci/verify-build.sh
 
   macos:
     name: macOS
@@ -250,9 +205,7 @@ jobs:
       - windows
       - solaris
       - style_check
-      - build_channels_linux
-      - build_channels_macos
-      - build_channels_windows
+      - verify_build
     # Github branch protection is exceedingly silly and treats "jobs skipped because a dependency
     # failed" as success. So we have to do some contortions to ensure the job fails if any of its
     # dependencies fails.

ci/build.sh → ci/verify-build.sh

@@ -8,12 +8,21 @@
 set -eux
 
 : "${TOOLCHAIN?The TOOLCHAIN environment variable must be set.}"
-: "${OS?The OS environment variable must be set.}"
 
 rust="$TOOLCHAIN"
 filter="${FILTER:-}"
 
-echo "Testing Rust $rust on $OS"
+case "$(uname -s)" in
+    Linux*)     os=linux ;;
+    Darwin*)    os=macos ;;
+    MINGW*)     os=windows ;;
+    *)
+        echo "Unknown system $(uname -s)"
+        exit 1
+        ;;
+esac
+
+echo "Testing Rust $rust on $os"
 
 if [ "$TOOLCHAIN" = "nightly" ] ; then
     rustup component add rust-src
@@ -198,40 +207,30 @@ i386-apple-ios \
 "
 
 # The targets are listed here alphabetically
-targets=""
-no_dist_targets=""
-
-case "${OS}" in
-    linux*)
-        targets="$rust_linux_targets"
-
-        if [ "$rust" = "nightly" ]; then
-            targets="$targets $rust_nightly_linux_targets"
-            no_dist_targets="$rust_linux_no_dist_targets"
-        fi
-
-        ;;
-    macos*)
-        targets="$rust_apple_targets"
-
-        if [ "$rust" = "nightly" ]; then
-            targets="$targets $rust_nightly_apple_targets"
-            no_dist_targets="$rust_apple_no_dist_targets"
-        fi
+if [ "$os" = "linux" ]; then
+    targets="$rust_linux_targets"
+    nightly_targets="$rust_nightly_linux_targets"
+    no_dist_targets="$rust_linux_no_dist_targets"
+elif [ "$os" = "macos" ]; then
+    targets="$rust_apple_targets"
+    nightly_targets="$rust_nightly_apple_targets"
+    no_dist_targets="$rust_apple_no_dist_targets"
+elif [ "$os" = "windows" ]; then
+    targets=${rust_nightly_windows_targets}
+else
+    exit 1
+fi
 
-        ;;
-    windows*)
-        targets=${rust_nightly_windows_targets}
-        ;;
-    *)
-        echo "Unrecognized OS $OS"
-        exit 1
-        ;;
-esac
+if [ "$rust" = "nightly" ]; then
+    targets="$targets $nightly_targets"
+else
+    # build-std requires nightly
+    no_dist_targets=""
+fi
 
 for target in $targets; do
     if echo "$target" | grep -q "$filter"; then
-        if [ "${OS}" = "windows" ]; then
+        if [ "$os" = "windows" ]; then
             TARGET="$target" ./ci/install-rust.sh
             test_target "$target"
         else
@@ -242,9 +241,9 @@ for target in $targets; do
     fi
 done
 
-for target in $no_dist_targets; do
+for target in ${no_dist_targets:-}; do
     if echo "$target" | grep -q "$filter"; then
-        if [ "${OS}" = "windows" ]; then
+        if [ "$os" = "windows" ]; then
             TARGET="$target" ./ci/install-rust.sh
             test_target "$target" 1
         else