feat: use /workspace/cache as a persistent cache between runs

Signed-off-by: Lars Wirzenius <liw@liw.fi>
Sponsored-by: author

3 files changed, 56 insertions, 1 deletions

diff --git a/ambient-driver.md b/ambient-driver.md
index eab1226..5e20085 100644
--- a/ambient-driver.md
+++ b/ambient-driver.md
@@ -225,3 +225,48 @@ then stdout contains "pre_actions:\n"
 then stdout contains "\nactions:\n"
 then stdout contains "\npost_actions:\n"
 ~~~
+# Cache persists between CI runs
+
+_Requirement:_ Cache data is persisted between CI runs.
+
+_Justification:_ This allows incrementally building a project after
+changes.
+
+_Stakeholders:_ Lars
+
+~~~scenario
+given an installed ambient-driver
+given file .config/ambient-driver/config.yaml from config.yaml
+given an Ambient VM image ambient.qcow2
+given file cache.yaml
+given a directory srcdir
+
+when I run ambient-driver run cache.yaml
+then file ambient.log contains "counter is now 1."
+
+when I run ambient-driver run cache.yaml
+then file ambient.log contains "counter is now 2."
+
+when I run ambient-driver run cache.yaml
+then file ambient.log contains "counter is now 3."
+~~~
+
+~~~{#cache.yaml .file .yaml}
+projects:
+  hello:
+    image: ambient.qcow2
+    source: srcdir
+    plan:
+    - action: shell
+      shell: |
+        cache=/workspace/cache
+        counter="$cache/counter"
+        if [ -e "$counter" ]; then
+            n="$(expr "$(cat "$counter")" + 1)"
+            echo "$n" > "$counter"
+        else
+            echo 1 > "$counter"
+        fi
+        echo "counter is now $(cat "$counter")."
+        find "$cache" -ls
+~~~
diff --git a/src/project.rs b/src/project.rs
index 1ef8fc0..2c5f23d 100644
--- a/src/project.rs
+++ b/src/project.rs
@@ -183,6 +183,11 @@ impl State {
         Ok(())
     }
 
+    /// Return cache directory for project.
+    pub fn cachedir(&self) -> PathBuf {
+        self.statedir.join("cache")
+    }
+
     /// Return latest commit that CI has run on.
     pub fn latest_commit(&self) -> Option<&str> {
         self.latest_commit.as_deref()
diff --git a/src/run.rs b/src/run.rs
index be343e2..c45310a 100644
--- a/src/run.rs
+++ b/src/run.rs
@@ -52,6 +52,11 @@ fn cmd_run(config: &EffectiveConfig, run: &RunCommand) -> Result<(), RunError> {
         if do_run {
             info!("{}: running CI on {}", name, project.source().display());
 
+            let cachedir = state.cachedir();
+            if !cachedir.exists() {
+                mkdir(&cachedir)?;
+            }
+
             debug!("Executing pre-plan steps");
             for action in project.pre_plan() {
                 action.execute(project, statedir)?;
@@ -96,7 +101,7 @@ fn cmd_run(config: &EffectiveConfig, run: &RunCommand) -> Result<(), RunError> {
             .with_artifact(&Some(artifact.clone()))
             .with_artifact_max_size(project.artifact_max_size())
             .with_dependencies(&Some(dependencies.clone()))
-            .with_cache(&None)
+            .with_cache(&Some(cachedir.clone()))
             .with_log(log);
             let exit = qemu.run()?;
             debug!("QEMU exit code {}", exit);