ci: Always run verify-build on Linux

Most of the targets are cross compiled anyway, and there isn't any
advantage to running on native platforms. Start running everything on
Linux which is the fastest and cheapest runner.

As part of this, introduce a way to run only half of the target list
from a single invocation. This is used to split the nightly job in two,
each now only taking about as long as the stable job.

(backport <#4780>)
(cherry picked from commit 56b916d)

Author: tgross35

.github/workflows/ci.yaml

@@ -51,12 +51,18 @@ jobs:
     name: Verify build
     strategy:
       matrix:
-        toolchain: [stable, nightly, 1.63.0]
-        os: [ubuntu-24.04, macos-15, windows-2025]
+        toolchain: [stable, 1.63.0]
         include:
+          # Nightly has a lot of targets, so split it in half
+          - toolchain: nightly
+            half: 1
+          - toolchain: nightly
+            half: 2
           - toolchain: beta
-            os: ubuntu-24.04
-    runs-on: ${{ matrix.os }}
+            only: '(aarch64|x86_64)' # just a spot check for beta
+          - toolchain: stable
+          - toolchain: 1.63.0 # msrv
+    runs-on: ubuntu-24.04
     timeout-minutes: 25
     env:
       TOOLCHAIN: ${{ matrix.toolchain }}
@@ -83,7 +89,10 @@ jobs:
           set -eux
           # Remove `-Dwarnings` at the MSRV since lints may be different
           [ "${{ matrix.toolchain }}" = "1.63.0" ] && export RUSTFLAGS=""
-          python3 ci/verify-build.py --toolchain "$TOOLCHAIN"
+          python3 ci/verify-build.py \
+            --toolchain "$TOOLCHAIN" \
+            ${{ matrix.only && format('--only "{0}"', matrix.only) }} \
+            ${{ matrix.half && format('--half "{0}"', matrix.half) }}
       - name: Target size after job completion
         run: du -sh target | sort -k 2
 

ci/verify-build.py

@@ -64,16 +64,6 @@ def __post_init__(self):
             # We will need to use build-std
             self.min_toolchain = Toolchain.NIGHTLY
 
-    def run_on(self) -> Os:
-        """MacOS CI runs all apple targets, Windows CI runs all Windows targets,
-        Linux CI handles everything else."""
-
-        if "apple" in self.name:
-            return Os.DARWIN
-        elif "windows" in self.name:
-            return Os.WINDOWS
-        return Os.LINUX
-
 
 FREEBSD_VERSIONS = [11, 12, 13, 14, 15]
 
@@ -324,6 +314,12 @@ def main():
     p.add_argument("--toolchain", required=True, help="Rust toolchain")
     p.add_argument("--only", help="only targets matching this regex")
     p.add_argument("--skip", help="skip targets matching this regex")
+    p.add_argument(
+        "--half",
+        type=int,
+        choices=[1, 2],
+        help="specify 1 or 2 to run half of the targets",
+    )
     args = p.parse_args()
 
     cfg = Cfg(toolchain_name=args.toolchain)
@@ -346,30 +342,26 @@ def main():
     targets = [t for t in targets if cfg.toolchain >= t.min_toolchain]
     eprint(f"Targets checkable with this toolchain: {len(targets)}")
 
-    # Targets get split among the diferent CI runners
-    targets = [t for t in targets if t.run_on() == cfg.os_]
-    eprint(f"Targets checked on this OS: {len(targets)}")
-
     # Apply filtering
     if args.only:
         targets = [t for t in targets if re.match(args.only, t.name)]
     if args.skip:
         targets = [t for t in targets if not re.match(args.skip, t.name)]
 
+    # Allow splitting the targets in half for time improvements
+    if args.half == 1:
+        targets = targets[0::2]
+    elif args.half == 2:
+        targets = targets[1::2]
+
     total = len(targets)
     eprint(f"Targets to run: {total}")
     assert total > 0, "some tests should be run"
 
     for i, target in enumerate(targets):
-        # HACK: We need to install the toolchain by name for most Windows toolchains,
-        # but not when cross compiling.
-        if cfg.os_ == Os.WINDOWS and "aarch64" not in target.name:
-            run(
-                ["sh", "./ci/install-rust.sh"], env=os.environ | {"TARGET": target.name}
-            )
-
-        eprint(f"::group::Target: {target.name} ({i}/{total})")
-        eprint(f"{ESC_CYAN}Checking target {target} ({i}/{total}){ESC_END}")
+        at = i + 1
+        eprint(f"::group::Target: {target.name} ({at}/{total})")
+        eprint(f"{ESC_CYAN}Checking target {target} ({at}/{total}){ESC_END}")
         test_target(cfg, target)
         eprint("::endgroup::")