feat(gh-actions/build-debian): Support running a workflow script at b…

…uild-source phase (#54)

When building some packages we may need to prepare the build environment
before preparing the source package, for example in some cases we may
need to enable git access (to compute the package version or similar) or
we may need to install tools that are used during debian source building
that are not provided in the archive (such as rust crates, hello
cargo-vendor-filterer!!).

So instead of polluting this generic action with package-specific
requirements, let's just make it support running a script that can do
more advanced configurations in the docker instance that is used only
during the source-preparation phase.

This is required in order to be able to do a `cargo install --root=/usr
cargo-vendor-filterer` to build the source package of rust programs as
required by authd in ubuntu/authd#130

UDENG-2343

.github/workflows/test-build-deb.yaml

@@ -88,6 +88,12 @@ jobs:
           docker-image: ubuntu:devel
           lintian: --fail-on error
           extra-source-build-deps: ''
+          extra-source-build-script: |
+            echo '$HOME' is "${HOME}"
+            echo "::group::Get some system information"
+            uname -a
+            cat /etc/os-release
+            echo "::endgroup::"
 
   lintian-to-md:
     name: Test lintian results parser to markdown

gh-actions/common/build-debian/action.yml

@@ -16,7 +16,14 @@ inputs:
     description: A list of extra build dependencies required during source build.
     required: false
     # FIXME: this should default to '', but we don't want to break job depending on us for now
-    default: 'ca-certificates git'
+    default: 'ca-certificates'
+  extra-source-build-script:
+    description: |
+      A script to run to prepare the source build machine.
+      This happens after the dependencies have been installed, but before
+      running `dpkg-buildpackage -S`.
+    required: false
+    default: ''
   lintian:
     required: false
     description: Arguments to pass to lintian, if any. Set to `skip` to skip the lintian check.
@@ -133,9 +140,17 @@ runs:
 
           echo "::group::Install build dependencies"
           apt build-dep .
+
+          GITHUB_TOKEN="${{ inputs.token }}"
+
           if [ -n "${{ inputs.extra-source-build-deps }}" ]; then
             # Install extra packages for build-deps, to allow downloading vendored sources
             deps=(${{ inputs.extra-source-build-deps }})
+
+            if [ -n "${GITHUB_TOKEN}" ]; then
+              deps+=(git)
+            fi
+
             apt install ${deps[@]}
           fi
           echo "::endgroup::"
@@ -144,11 +159,19 @@ runs:
             git config --system --add safe.directory "${{ github.workspace }}"
           fi
 
-          GITHUB_TOKEN="${{ inputs.token }}"
           if [ -n "${GITHUB_TOKEN}" ]; then
             git config --system url."https://api:${GITHUB_TOKEN}@github.com/".insteadOf "https://github.com/"
           fi
 
+          if [ -n "${{ inputs.extra-source-build-script != '' && 'true' || '' }}" ]; then
+            echo "::group::Run source build script"
+            (
+              set -eux
+              ${{ inputs.extra-source-build-script }}
+            )
+            echo "::endgroup::"
+          fi
+
           echo "::group::Build debian source package"
           dpkg-buildpackage -D -S --sanitize-env
           echo "::endgroup::"