Make GHA config more efficient (#10383)

A few things here:

* Build the debs for single distro for each PR, so that we can see if it breaks. Do the same for develop. Building all the debs ties up the GHA workers for ages.
* Stop building the debs for release branches. Again, it takes ages, and I don't think anyone is actually going to stop and look at them. We'll know they are working when we make an RC.
* Change the configs so that if we manually cancel a workflow, it actually does something.

3 files changed, 21 insertions, 15 deletions

diff --git a/.github/workflows/release-artifacts.yml b/.github/workflows/release-artifacts.yml
index f292d703ed..325c1f7d39 100644
--- a/.github/workflows/release-artifacts.yml
+++ b/.github/workflows/release-artifacts.yml
@@ -3,28 +3,33 @@
 name: Build release artifacts
 
 on:
+  # we build on PRs and develop to (hopefully) get early warning
+  # of things breaking (but only build one set of debs)
+  pull_request:
   push:
-    # we build on develop and release branches to (hopefully) get early warning
-    # of things breaking
-    branches: ["develop", "release-*"]
+    branches: ["develop"]
 
-    # we also rebuild on tags, so that we can be sure of picking the artifacts
-    # from the right tag.
+    # we do the full build on tags.
     tags: ["v*"]
 
 permissions:
   contents: write
 
 jobs:
-  # first get the list of distros to build for.
   get-distros:
+    name: "Calculate list of debian distros"
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2
       - uses: actions/setup-python@v2
       - id: set-distros
         run: |
-          echo "::set-output name=distros::$(scripts-dev/build_debian_packages --show-dists-json)"
+          # if we're running from a tag, get the full list of distros; otherwise just use debian:sid
+          dists='["debian:sid"]'
+          if [[ $GITHUB_REF == refs/tags/* ]]; then
+              dists=$(scripts-dev/build_debian_packages --show-dists-json)
+          fi
+          echo "::set-output name=distros::$dists"
     # map the step outputs to job outputs
     outputs:
       distros: ${{ steps.set-distros.outputs.distros }}
@@ -66,7 +71,7 @@ jobs:
   # if it's a tag, create a release and attach the artifacts to it
   attach-assets:
     name: "Attach assets to release"
-    if: startsWith(github.ref, 'refs/tags/')
+    if: ${{ !failure() && !cancelled() && startsWith(github.ref, 'refs/tags/') }}
     needs:
       - build-debs
       - build-sdist
diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index bf36ee1cdf..505bac1308 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -65,14 +65,14 @@ jobs:
 
   # Dummy step to gate other tests on without repeating the whole list
   linting-done:
-    if: ${{ always() }} # Run this even if prior jobs were skipped
+    if: ${{ !cancelled() }} # Run this even if prior jobs were skipped
     needs: [lint, lint-crlf, lint-newsfile, lint-sdist]
     runs-on: ubuntu-latest
     steps:
       - run: "true"
 
   trial:
-    if: ${{ !failure() }} # Allow previous steps to be skipped, but not fail
+    if: ${{ !cancelled() && !failure() }} # Allow previous steps to be skipped, but not fail
     needs: linting-done
     runs-on: ubuntu-latest
     strategy:
@@ -131,7 +131,7 @@ jobs:
           || true
 
   trial-olddeps:
-    if: ${{ !failure() }} # Allow previous steps to be skipped, but not fail
+    if: ${{ !cancelled() && !failure() }} # Allow previous steps to be skipped, but not fail
     needs: linting-done
     runs-on: ubuntu-latest
     steps:
@@ -156,7 +156,7 @@ jobs:
 
   trial-pypy:
     # Very slow; only run if the branch name includes 'pypy'
-    if: ${{ contains(github.ref, 'pypy') && !failure() }}
+    if: ${{ contains(github.ref, 'pypy') && !failure() && !cancelled() }}
     needs: linting-done
     runs-on: ubuntu-latest
     strategy:
@@ -185,7 +185,7 @@ jobs:
           || true
 
   sytest:
-    if: ${{ !failure() }}
+    if: ${{ !failure() && !cancelled() }}
     needs: linting-done
     runs-on: ubuntu-latest
     container:
@@ -245,7 +245,7 @@ jobs:
             /logs/**/*.log*
 
   portdb:
-    if: ${{ !failure() }} # Allow previous steps to be skipped, but not fail
+    if: ${{ !failure() && !cancelled() }} # Allow previous steps to be skipped, but not fail
     needs: linting-done
     runs-on: ubuntu-latest
     strategy:
@@ -286,7 +286,7 @@ jobs:
       - run: .buildkite/scripts/test_synapse_port_db.sh
 
   complement:
-    if: ${{ !failure() }}
+    if: ${{ !failure() && !cancelled() }}
     needs: linting-done
     runs-on: ubuntu-latest
     container:
diff --git a/changelog.d/10383.misc b/changelog.d/10383.misc
new file mode 100644
index 0000000000..952c1e77a8
--- /dev/null
+++ b/changelog.d/10383.misc
@@ -0,0 +1 @@
+Make the Github Actions workflow configuration more efficient.