Add some basic devenv tests

devenv v1.0 will add proper testing infrastructure, but for now this is a
noddy solution.

.ci/scripts/build-all-dev-envs.sh

@@ -15,16 +15,19 @@ for project in "$PROJECT_FLAKES_DIR"/*/ ; do
   # Extract the git URL of the project. We often need the files of the
   # project locally in order to build the development shell:
   url=$(grep "^# ci.project-url:" "$PROJECT_FLAKES_DIR/$project/default.nix" | awk -F': ' '{print $2}')
+  # Extract the CI test command of the project. We'll use this to check
+  # that the development environment built successfully.
+  cmd=$(grep "^# ci.test-command:" "$PROJECT_FLAKES_DIR/$project/default.nix" | awk -F': ' '{print $2}')
   echo "Cloning repo: $url"
   # Clone the project to a directory with the same name.
-  git clone --depth 1 -q "$url" "$project"
+  git clone --depth 1 --single-branch -q "$url" "$project"
   # Enter the project directory.
   cd "$project"
   # Show the generated outputs of the flake.
   nix flake show ..
   # Attempt to build and enter the development environment,
-  # then immediately exit the built shell.
-  nix develop --impure ..#"$project" -c "true"
+  # then run the specified test command.
+  nix develop --impure ..#"$project" -c bash -c "$cmd"
   # Leave the project directory.
   cd ..
   # Delete the project directory.

project-flakes/complement/module.nix

@@ -1,4 +1,5 @@
 # ci.project-url: https://github.com/matrix-org/complement
+# ci.test-command: go build ./tests/...
 { pkgs, ... }:
 
 {

project-flakes/element-web/module.nix

@@ -1,4 +1,5 @@
 # ci.project-url: https://github.com/vector-im/element-web
+# ci.test-command: yarn install && yarn build
 { pkgs, ... }:
 
 {

project-flakes/synapse/module.nix

@@ -1,4 +1,5 @@
 # ci.project-url: https://github.com/matrix-org/synapse
+# ci.test-command: python -m synapse.app.homeserver --server-name local -c homeserver.yaml --generate-config --report-stats=no
 { pkgs, ... }:
 
 let

project-flakes/sytest/module.nix

@@ -1,4 +1,5 @@
 # ci.project-url: https://github.com/matrix-org/sytest
+# ci.test-command: perl --version
 { pkgs, ... }:
 
 {