build-jobs: use parallel:matrix instead of copy-pasting job definitions

This has the additional benefit that the job is always defined, and
then we can just add the placeholder as any other job

Part-of: https://gitlab.postmarketos.org/postmarketOS/pmaports/-/merge_requests/6693
[ci:skip-build]: already built successfully in CI

.ci/build-jobs.yaml.j2

@@ -17,20 +17,9 @@ workflow:
   rules:
     - if: $CI_PIPELINE_SOURCE == "parent_pipeline"
 
-{% if archs|length == 0 %}
-# Needed because gitlab fails if no jobs are ran:
-#  - https://gitlab.com/gitlab-org/gitlab/-/issues/368248
-# This applies to `when: manual` is used on all jobs.
-placeholder:
-  stage: build
-  script:
-    - 'true'
-{% endif %}
-
 .build:
-  # Create jobs, but don't run them unless this is
+  # Create jobs, but do not run them unless this is
   # overriden in jobs that extend it
-  when: manual
   stage: build
   interruptible: true
   before_script:
@@ -51,57 +40,28 @@ placeholder:
       - keys/
   timeout: 10 h
 
-build-x86_64:
-{% if ('x86_64' in archs) %}
-  when: always
-{% endif %}
+build:
   extends: .build
-  script:
-    - .ci/build-x86_64.sh
-
-build-x86:
-{% if ('x86' in archs) %}
-  when: always
+  parallel:
+    matrix:
+{% for arch in archs %}
+      - ARCH: {{ arch }}
+        TAG: {{ archtag[arch] }}
+{% endfor %}
+{% if archs|length == 0 %}
+      - ARCH: placeholder
+        TAG: shared
 {% endif %}
-  extends: .build
+  tags:
+    - $TAG
   script:
-    - .ci/build-x86.sh
-
-build-aarch64:
-{% if ('aarch64' in archs) %}
-  when: always
+# Needed because gitlab fails if no jobs are ran:
+#  - https://gitlab.com/gitlab-org/gitlab/-/issues/368248
+{% if archs|length == 0 %}
+    - 'true'
+{% else %}
+    - .ci/build-$ARCH.sh
 {% endif %}
-  extends: .build
-  tags: [arm64]
-  script:
-    - .ci/build-aarch64.sh
-
-build-armv7:
-{% if ('armv7' in archs) %}
-  when: always
-{% endif %}
-  extends: .build
-  tags: [qemu]
-  script:
-    - .ci/build-armv7.sh
-
-build-armhf:
-{% if ('armhf' in archs) %}
-  when: always
-{% endif %}
-  extends: .build
-  tags: [qemu]
-  script:
-    - .ci/build-armhf.sh
-
-build-riscv64:
-{% if ('riscv64' in archs) %}
-  when: always
-{% endif %}
-  extends: .build
-  tags: [qemu]
-  script:
-    - .ci/build-riscv64.sh
 
 # Hardware testing
 
@@ -139,7 +99,12 @@ prepare-{{ device.name }}:
         - {{ kernel }}
       {%- endfor %}
   {%- endif %}
-  needs: ["build-{{ device.arch }}"]
+  needs:
+    - job: "build"
+      parallel:
+        matrix:
+          - ARCH: "{{ device.arch }}"
+            TAG: "{{ archtag[device.arch] }}"
   variables:
     DEVICE_NAME: {{ device.name }}
     # NOTE: All the packages that may influence testing should have an

.ci/lib/generate_build_jobs.py

@@ -141,6 +141,23 @@ class Device:
         return supported_devices
 
 
+class ArchTagSet(set):
+    supported_arches = [
+        Arch.x86_64,
+        Arch.x86,
+        Arch.aarch64,
+        Arch.armv7,
+        Arch.armhf,
+        Arch.riscv64,
+    ]
+
+    def update(self, iterable):
+        # This ignores things like !armv7, that could be a follow-up optimization
+        if 'noarch' in iterable or 'all' in iterable:
+            iterable = [arch for arch in self.supported_arches]
+        super().update([Arch(arch) for arch in iterable if Arch(arch) in self.supported_arches])
+
+
 if __name__ == "__main__":
     # Needs input to output if we should create the jobs
     if len(sys.argv) != 3:
@@ -163,7 +180,7 @@ if __name__ == "__main__":
     # Get the list of supported devices
     supported_devices = Device.supported_devices()
 
-    archs = set()
+    archs = ArchTagSet()
     devices_under_test = set()
     packages_modified = set()
     # Get and print modified packages
@@ -189,19 +206,27 @@ if __name__ == "__main__":
             if apkbuild['pkgname'] in device.dependencies:
                 devices_under_test.add(device)
 
-    # This ignores things like !armv7, that could be a follow-up optimization
-    if 'noarch' in archs or 'all' in archs:
-        archs = set([str(arch) for arch in Arch.supported()])
-
     if common.commit_message_has_string("[ci:skip-build]"):
         print("User requested skipping build, not creating child pipeline file")
-        archs = set()
+        archs = ArchTagSet()
         devices_under_test = set()
 
     print(f"Architectures to build: {archs}")
     print(f"Devices under test: {devices_under_test}")
 
     with open(template) as f:
-        rendered = Template(f.read()).render(archs=archs, devices_under_test=devices_under_test, packages_modified=packages_modified)
+        rendered = Template(f.read()).render(
+            archs=archs,
+            devices_under_test=devices_under_test,
+            packages_modified=packages_modified,
+            archtag={
+                Arch.x86_64: "shared",
+                Arch.x86: "shared",
+                Arch.aarch64: "arm64",
+                Arch.armv7: "qemu",
+                Arch.armhf: "qemu",
+                Arch.riscv64: "qemu",
+            },
+        )
         with open(child_pipeline, "w") as fw:
             fw.write(rendered)