PR builds and generation skip what is already on the upload channel

.github/workflows/main.yaml

@@ -61,6 +61,8 @@ jobs:
         distro: ${{ fromJSON(needs.plan.outputs.distros) }}
     env:
       DISTRO: ${{ matrix.distro }}
+      # while uploads go to a test channel, packages already there aren't built again
+      ROBOSTACK_UPLOAD_CHANNEL: ${{ vars.ROBOSTACK_UPLOAD_CHANNEL }}
       DRY_RUN: ${{ inputs.dry_run || 'false' }}
     steps:
       - name: Bot token (pushing workflow files needs more than GITHUB_TOKEN)

.github/workflows/testpr.yaml

@@ -84,6 +84,8 @@ jobs:
     env:
       DISTRO: ${{ matrix.distro }}
       PLATFORM: ${{ matrix.target.platform }}
+      # while uploads go to a test channel, packages already there aren't built again
+      ROBOSTACK_UPLOAD_CHANNEL: ${{ vars.ROBOSTACK_UPLOAD_CHANNEL }}
       # rattler-build writes to distros/<d>/work/output, or to CONDA_BLD_PATH (win-64)
       CACHE_DIR: ${{ matrix.target.platform == 'win-64' && 'C:/bld/win-64' || format('distros/{0}/work/output/{1}', matrix.distro, matrix.target.platform) }}
     steps:

tools/robostack.py

@@ -167,10 +167,13 @@ def prepare(distro: str) -> Path:
         shutil.rmtree(w / stale, ignore_errors=True)
     for stale in ("pkg_additional_info.yaml", "robostack.yaml", "packages_ignore.yaml", "packages-ignore.yaml"):
         (w / stale).unlink(missing_ok=True)
+    # packages already on the channel aren't built again; while uploads go to another
+    # channel (ROBOSTACK_UPLOAD_CHANNEL, e.g. a test channel), those count too
+    skip = [channel_url(distro)] + ([extra] if (extra := upload_channel_url()) else [])
     (w / "vinca.yaml").write_text(
         f"# Generated by `pixi run rs {distro} prepare`; edit distros/{distro}/vinca.yaml or shared/vinca.yaml.\n"
         "extends: ../vinca.yaml\n"
-        f"skip_existing:\n  - {channel_url(distro)}/\n"
+        "skip_existing:\n" + "".join(f"  - {url}/\n" for url in skip)
     )
     # vinca-gha inlines ./.scripts/build_win.bat into the Windows workflow
     shutil.rmtree(w / ".scripts", ignore_errors=True)
@@ -288,10 +291,15 @@ def task(distro: str, name: str, args: list[str]) -> int:
         return run(py + [str(TOOLS / "check_dependency_compat.py"), *args], w)
     if name == "gap-report":
         return run(py + [str(TOOLS / "build_gap_report.py"), *args], w)
-    if name in ("build", "build-one") and not any((w / "recipes").glob("*/recipe.yaml")):
-        print(f"No recipes in {(w / 'recipes').relative_to(ROOT)}: run `pixi run rs {distro} generate-recipes` first",
-              file=sys.stderr)
-        return 1
+    if name in ("build", "build-one"):
+        if not (w / "recipes").is_dir():
+            print(f"No {(w / 'recipes').relative_to(ROOT)}: run `pixi run rs {distro} generate-recipes` first",
+                  file=sys.stderr)
+            return 1
+        if not any((w / "recipes").glob("*/recipe.yaml")):
+            # generated, but every package is already built (on the channel)
+            print(f"Nothing to build: {(w / 'recipes').relative_to(ROOT)} is empty")
+            return 0
     if name == "build":
         return run(rattler_build(distro, ["--recipe-dir", "./recipes", *args]), w)
     if name == "build-ci":  # used by .scripts/build_unix.sh / build_win.bat