PR builds: build:linux / build:osx / build:win labels limit the platforms

.github/workflows/testpr.yaml

@@ -27,9 +27,10 @@ jobs:
     runs-on: ubuntu-latest
     permissions:
       contents: read
-      pull-requests: read  # the build:<distro> labels
+      pull-requests: read  # the build:<distro> and build:<platform> labels
     outputs:
       distros: ${{ steps.plan.outputs.distros }}
+      targets: ${{ steps.plan.outputs.targets }}
     steps:
       - uses: actions/checkout@v6
         with:
@@ -50,6 +51,7 @@ jobs:
           SELECTED: ${{ inputs.distros }}
           GH_TOKEN: ${{ github.token }}
         run: |
+          labels="[]"
           if [ -n "$SELECTED" ]; then
             distros=$(pixi run python -c 'import json,os; print(json.dumps(os.environ["SELECTED"].split()))')
           elif [ -n "$BASE" ]; then
@@ -61,6 +63,8 @@ jobs:
             distros=$(pixi run python tools/robostack.py changed-distros --base HEAD --all)
           fi
           echo "distros=$distros" | tee -a "$GITHUB_OUTPUT"
+          # build:linux / build:osx / build:win labels limit the platforms (all without)
+          echo "targets=$(pixi run python tools/robostack.py build-targets --labels "$labels")" | tee -a "$GITHUB_OUTPUT"
 
   check:
     runs-on: ubuntu-latest
@@ -142,12 +146,7 @@ jobs:
       fail-fast: false
       matrix:
         distro: ${{ fromJSON(needs.plan.outputs.distros) }}
-        target:
-          - { os: ubuntu-latest, platform: linux-64 }
-          - { os: ubuntu-24.04-arm, platform: linux-aarch64 }
-          - { os: macos-15-intel, platform: osx-64 }
-          - { os: macos-15, platform: osx-arm64 }
-          - { os: windows-2022, platform: win-64 }
+        target: ${{ fromJSON(needs.plan.outputs.targets) }}  # tools/robostack.py BUILD_TARGETS
     name: ${{ matrix.distro }} ${{ matrix.target.platform }}
     runs-on: ${{ matrix.target.os }}
     env:

AGENTS.md

@@ -72,6 +72,8 @@ should edit a shared file at a time.
 - A PR builds the distributions it changes (all of them if it touches anything
   outside `distros/<d>/`). To build only some, add `build:<distro>` labels (e.g.
   `build:humble`), then push or re-run the build (adding a label doesn't start one).
+  `build:linux` / `build:osx` / `build:win` (or `build:<platform>`) limit the platforms;
+  remove them for one full build before merging.
 - After a merge, `main.yaml` regenerates the staged build branches
   `buildbranch_<distro>_<platform>`; uploads go to the channel in `distro.yaml`, or to
   the repository variable `ROBOSTACK_UPLOAD_CHANNEL`.

README.md

@@ -112,6 +112,9 @@ that (e.g. a humble rebuild that also changes `shared/` or `tools/`), add the la
 `build:humble` (one per distribution to build), then push or re-run the build: adding a
 label doesn't start one by itself. Nothing has to be reset before merging. A PR that
 changes no packages (tooling, CI, docs) gets `build:none`: only the checks run.
+Platform labels limit the platforms the same way: `build:linux`, `build:osx`, `build:win`
+(or one platform, e.g. `build:linux-64`), e.g. to iterate on Windows fixes without
+waiting for the macOS runners; remove them for a full build before merging.
 
 ### CI
 

tools/robostack.py

@@ -581,6 +581,16 @@ def generate_gha(distro: str, args: list[str]) -> int:
 
 
 NO_BUILD_LABEL = "build:none"  # only the checks (tooling, CI or docs changes)
+# the pull-request build's platforms and their runners; build:linux / build:osx / build:win
+# (or build:<platform>) labels limit a PR build to those
+BUILD_TARGETS = [
+    {"os": "ubuntu-latest", "platform": "linux-64"},
+    {"os": "ubuntu-24.04-arm", "platform": "linux-aarch64"},
+    {"os": "macos-15-intel", "platform": "osx-64"},
+    {"os": "macos-15", "platform": "osx-arm64"},
+    {"os": "windows-2022", "platform": "win-64"},
+]
+PLATFORM_LABELS = {"linux": ("linux-64", "linux-aarch64"), "osx": ("osx-64", "osx-arm64"), "win": ("win-64",)}
 
 
 def build_distros(changed: list[str], labels: list[str]) -> list[str]:
@@ -589,13 +599,24 @@ def build_distros(changed: list[str], labels: list[str]) -> list[str]:
     touches shared files), else the changed ones."""
     if NO_BUILD_LABEL in labels:
         return []
-    selected = sorted({label.split(":", 1)[1] for label in labels if label.startswith("build:")})
+    platforms = set(PLATFORM_LABELS) | {t["platform"] for t in BUILD_TARGETS}
+    selected = sorted({label.split(":", 1)[1] for label in labels if label.startswith("build:")} - platforms)
     unknown = sorted(set(selected) - set(distros()))
     if unknown:
         raise SystemExit(f"build:<distro> labels name unknown distributions: {', '.join(unknown)}")
     return selected or changed
 
 
+def build_targets(labels: list[str]) -> list[dict]:
+    """The platforms a pull request builds: those of its build:linux / build:osx / build:win
+    (or build:<platform>) labels when it has any, else all of them."""
+    wanted = set()
+    for label in labels:
+        name = label.split(":", 1)[1] if label.startswith("build:") else ""
+        wanted |= set(PLATFORM_LABELS.get(name, ())) | ({name} & {t["platform"] for t in BUILD_TARGETS})
+    return [t for t in BUILD_TARGETS if not wanted or t["platform"] in wanted]
+
+
 def changed_distros(base: str) -> list[str]:
     # no common history (main's history was rewritten and force-pushed): nothing to
     # diff against, so every distribution counts as changed
@@ -627,6 +648,12 @@ def main() -> int:
         changed = distros() if ns.all else changed_distros(ns.base)
         print(json.dumps(build_distros(changed, json.loads(ns.labels))))
         return 0
+    if len(sys.argv) >= 2 and sys.argv[1] == "build-targets":
+        parser = argparse.ArgumentParser(prog="rs build-targets")
+        parser.add_argument("--labels", default="[]", help="JSON list of the pull request's labels")
+        ns = parser.parse_args(sys.argv[2:])
+        print(json.dumps(build_targets(json.loads(ns.labels))))
+        return 0
     if len(sys.argv) < 3:
         print(__doc__)
         print("distributions:", ", ".join(distros()))

tools/tests/test_bot_commands.py

@@ -235,6 +235,19 @@ def test_build_distros_labels_override_the_changed_ones():
     assert rs.build_distros(rs.distros(), ["build:none", "build:humble"]) == []
     with pytest.raises(SystemExit):
         rs.build_distros([], ["build:kinetic"])
+    # platform labels don't select distributions
+    assert rs.build_distros(["humble", "jazzy"], ["build:win", "build:linux-64"]) == ["humble", "jazzy"]
+    assert rs.build_distros(rs.distros(), ["build:jazzy", "build:osx"]) == ["jazzy"]
+
+
+def test_build_targets_from_platform_labels():
+    platforms = lambda labels: [t["platform"] for t in rs.build_targets(labels)]
+    assert platforms([]) == ["linux-64", "linux-aarch64", "osx-64", "osx-arm64", "win-64"]
+    assert platforms(["build:jazzy", "automerge"]) == platforms([])
+    assert platforms(["build:win"]) == ["win-64"]
+    assert platforms(["build:linux", "build:win"]) == ["linux-64", "linux-aarch64", "win-64"]
+    assert platforms(["build:osx-arm64"]) == ["osx-arm64"]
+    assert rs.build_targets(["build:win"]) == [{"os": "windows-2022", "platform": "win-64"}]
 
 
 def test_run_build_retries_network_errors(tmp_path, monkeypatch):