Convert the empty-stratum test into a yarn

We will use MorphologyLoader.load_from_file() to load morphologies
from a temporary file, so the output will be unpredictable. That
will break this test, so we may as well convert it into a yarn
to fix it.

2 files changed, 37 insertions, 0 deletions

diff --git a/yarns/building.yarn b/yarns/building.yarn
index 90daf069..b5e46b73 100644
--- a/yarns/building.yarn
+++ b/yarns/building.yarn
@@ -101,3 +101,14 @@ repos cached locally.
     AND the distbuild worker is terminated
     AND the communal cache server is terminated
     AND the git server is shut down
+
+Empty strata don't build
+------------------------
+
+    SCENARIO empty-strata
+    GIVEN a workspace
+    AND a git server
+    WHEN the user checks out the system branch called empty-stratum
+    AND the user attempts to build the system systems/empty-stratum-system.morph in branch empty-stratum
+    THEN morph failed
+    FINALLY the git server is shut down
diff --git a/yarns/implementations.yarn b/yarns/implementations.yarn
index 8b43286f..2557e2e5 100644
--- a/yarns/implementations.yarn
+++ b/yarns/implementations.yarn
@@ -336,6 +336,32 @@ another to hold a chunk.
     git commit -m Initial.
     git tag -a "test-tag" -m "Tagging test-tag"
 
+    # A new branch is created here as the presence of an empty stratum will
+    # break any morph commands which load all definitions in the repository.
+    git checkout -b empty-stratum
+
+    install -m644 -D /dev/stdin << EOF "systems/empty-stratum-system.morph"
+    name: empty-stratum-system
+    kind: system
+    arch: $arch
+    strata:
+    - name: build-essential
+      morph: strata/build-essential.morph
+    - name: core
+      morph: strata/core.morph
+    - name: empty
+      morph: strata/empty.morph
+    EOF
+
+    install -m644 -D /dev/stdin << EOF "strata/empty.morph"
+    name: empty
+    kind: stratum
+    EOF
+
+    git add .
+    git commit -m 'Add an empty stratum'
+    git checkout master
+
     # Start a git daemon to serve our git repositories
     port_file="$DATADIR/git-daemon-port"
     pid_file="$DATADIR/git-daemon-pid"