fix(hm): discovery prefers Python + empty registry for pipeline-less repos

crates/hm-dsl-engine/src/detect.rs

@@ -5,43 +5,83 @@ use anyhow::{Context, bail};
 use crate::DslLanguage;
 
 /// Detect the DSL language used in a project by scanning `.harmont/` for file
-/// extensions.
+/// extensions. Prefers **TypeScript** when both are present (the `hm run`
+/// default).
 ///
 /// # Errors
 ///
 /// - The `.harmont/` directory does not exist.
 /// - No `.py` or `.ts` files are found inside `.harmont/`.
-/// - Both `.py` and `.ts` files are present (mixed languages).
 pub fn detect_language(repo_root: &Path) -> anyhow::Result<DslLanguage> {
     let harmont_dir = repo_root.join(".harmont");
+    if !harmont_dir.is_dir() {
+        bail!("no .harmont/ directory found in {}", repo_root.display());
+    }
+    match scan_extensions(repo_root)? {
+        // When both languages are present, prefer TypeScript.
+        (_, true) => Ok(DslLanguage::TypeScript),
+        (true, false) => Ok(DslLanguage::Python),
+        (false, false) => bail!("no .py or .ts files found in {}", harmont_dir.display()),
+    }
+}
 
+/// Like [`detect_language`] but prefers **Python** when both are present.
+///
+/// Used by the machine-facing `hm pipelines` / `hm render` commands that the
+/// backend shells out to: the Python path is the fully-supported one (the
+/// discovery envelope is Python-only today), so a repo carrying both a `.py`
+/// and a redundant `.ts` resolves to Python rather than the unsupported TS
+/// registry. `hm run` keeps the TypeScript-preferring [`detect_language`].
+///
+/// # Errors
+///
+/// - The `.harmont/` directory does not exist.
+/// - No `.py` or `.ts` files are found inside `.harmont/`.
+pub fn detect_language_python_first(repo_root: &Path) -> anyhow::Result<DslLanguage> {
+    let harmont_dir = repo_root.join(".harmont");
     if !harmont_dir.is_dir() {
         bail!("no .harmont/ directory found in {}", repo_root.display());
     }
+    match scan_extensions(repo_root)? {
+        (true, _) => Ok(DslLanguage::Python),
+        (false, true) => Ok(DslLanguage::TypeScript),
+        (false, false) => bail!("no .py or .ts files found in {}", harmont_dir.display()),
+    }
+}
+
+/// True when `.harmont/` exists and holds at least one `.py` or `.ts` file.
+///
+/// The backend fans pipeline discovery out across every repo in an
+/// installation, most of which declare no pipelines at all. Those repos should
+/// yield an empty registry, not an error — callers use this to short-circuit to
+/// an empty envelope instead of calling [`detect_language_python_first`].
+#[must_use]
+pub fn has_pipeline_files(repo_root: &Path) -> bool {
+    matches!(scan_extensions(repo_root), Ok((py, ts)) if py || ts)
+}
+
+/// Scan `.harmont/` and report `(has_py, has_ts)`. A missing `.harmont/`
+/// directory yields `(false, false)`; an unreadable one is an error.
+fn scan_extensions(repo_root: &Path) -> anyhow::Result<(bool, bool)> {
+    let harmont_dir = repo_root.join(".harmont");
+    if !harmont_dir.is_dir() {
+        return Ok((false, false));
+    }
 
     let entries = std::fs::read_dir(&harmont_dir)
         .with_context(|| format!("failed to read {}", harmont_dir.display()))?;
 
     let mut has_py = false;
     let mut has_ts = false;
-
     for entry in entries {
         let entry = entry?;
-        let path = entry.path();
-
-        match path.extension().and_then(|e| e.to_str()) {
+        match entry.path().extension().and_then(|e| e.to_str()) {
             Some("py") => has_py = true,
             Some("ts") => has_ts = true,
             _ => {}
         }
     }
-
-    match (has_py, has_ts) {
-        // When both languages are present, prefer TypeScript.
-        (_, true) => Ok(DslLanguage::TypeScript),
-        (true, false) => Ok(DslLanguage::Python),
-        (false, false) => bail!("no .py or .ts files found in {}", harmont_dir.display()),
-    }
+    Ok((has_py, has_ts))
 }
 
 #[cfg(test)]
@@ -107,4 +147,47 @@ mod tests {
             "unexpected error: {msg}"
         );
     }
+
+    #[test]
+    fn python_first_prefers_python_when_mixed() {
+        let tmp = setup(&["ci.py", "deploy.ts"]);
+        assert_eq!(
+            detect_language_python_first(tmp.path()).unwrap(),
+            DslLanguage::Python
+        );
+    }
+
+    #[test]
+    fn python_first_falls_back_to_typescript_when_only_ts() {
+        let tmp = setup(&["ci.ts"]);
+        assert_eq!(
+            detect_language_python_first(tmp.path()).unwrap(),
+            DslLanguage::TypeScript
+        );
+    }
+
+    #[test]
+    fn python_first_no_harmont_dir_is_error() {
+        let tmp = TempDir::new().unwrap();
+        let err = detect_language_python_first(tmp.path()).unwrap_err();
+        assert!(
+            err.to_string().contains("no .harmont/ directory"),
+            "unexpected error: {err}"
+        );
+    }
+
+    #[test]
+    fn has_pipeline_files_true_for_py_and_ts() {
+        assert!(has_pipeline_files(setup(&["ci.py"]).path()));
+        assert!(has_pipeline_files(setup(&["ci.ts"]).path()));
+        assert!(has_pipeline_files(setup(&["ci.py", "deploy.ts"]).path()));
+    }
+
+    #[test]
+    fn has_pipeline_files_false_for_missing_or_empty_harmont() {
+        // No .harmont/ directory at all.
+        assert!(!has_pipeline_files(TempDir::new().unwrap().path()));
+        // .harmont/ exists but declares no .py/.ts files.
+        assert!(!has_pipeline_files(setup(&["README.md"]).path()));
+    }
 }

crates/hm/src/cli/pipelines.rs

@@ -11,19 +11,36 @@ pub struct PipelinesArgs {
     pub dir: Option<PathBuf>,
 }
 
+/// Empty discovery envelope, emitted when a repo declares no pipelines. Mirrors
+/// the shape of `harmont.dump_registry_json()` so backend discovery parses it
+/// the same way (it reads only the `pipelines` array).
+const EMPTY_ENVELOPE: &str = r#"{"schema_version":"1","pipelines":[]}"#;
+
 /// Print the discovery envelope JSON (all pipelines) to stdout.
 ///
+/// A repo with no `.harmont/` directory (or one with no `.py`/`.ts` files)
+/// declares no pipelines and yields the empty envelope rather than an error —
+/// the backend fans discovery out across every repo in an installation, most of
+/// which carry no pipelines. When both Python and TypeScript are present, Python
+/// wins (the registry dump is Python-only today).
+///
 /// # Errors
 ///
-/// Returns an error if the language can't be detected, the engine can't start,
-/// or the DSL runtime fails to evaluate the pipelines.
+/// Returns an error if the engine can't start or the DSL runtime fails to
+/// evaluate the pipelines.
 pub async fn run(args: PipelinesArgs) -> Result<()> {
     let repo_root = match args.dir {
         Some(d) => d,
         None => std::env::current_dir().context("cannot determine current directory")?,
     };
 
-    let lang = detect::detect_language(&repo_root).context("detecting pipeline language")?;
+    if !detect::has_pipeline_files(&repo_root) {
+        print!("{EMPTY_ENVELOPE}");
+        return Ok(());
+    }
+
+    let lang =
+        detect::detect_language_python_first(&repo_root).context("detecting pipeline language")?;
     let engine = engine_for(lang).context("initializing DSL engine")?;
     let json = engine
         .registry_json(&repo_root)

crates/hm/src/cli/render.rs

@@ -17,6 +17,9 @@ pub struct RenderArgs {
 
 /// Render one pipeline's v0 IR JSON to stdout without executing it.
 ///
+/// When both Python and TypeScript are present, Python wins (the supported
+/// backend path), matching `hm pipelines`.
+///
 /// # Errors
 ///
 /// Returns an error if the language can't be detected, the engine can't start,
@@ -28,7 +31,8 @@ pub async fn run(args: RenderArgs) -> Result<()> {
         None => std::env::current_dir().context("cannot determine current directory")?,
     };
 
-    let lang = detect::detect_language(&repo_root).context("detecting pipeline language")?;
+    let lang =
+        detect::detect_language_python_first(&repo_root).context("detecting pipeline language")?;
     let engine = engine_for(lang).context("initializing DSL engine")?;
     let json = engine
         .render_pipeline_json(&repo_root, &args.slug)

crates/hm/tests/cmd_pipelines.rs

@@ -45,3 +45,26 @@ def ci() -> hm.Step:
     assert_eq!(v["pipelines"][0]["slug"], "ci");
     assert_eq!(v["pipelines"][0]["triggers"][0]["event"], "push");
 }
+
+#[test]
+fn pipelines_emits_empty_envelope_when_no_harmont_dir() {
+    // A repo that declares no pipelines must yield an empty envelope, not an
+    // error (the backend fans discovery across every repo in an installation,
+    // most of which carry no `.harmont/`). No python3 needed — this short-
+    // circuits before the DSL engine, so the test always runs.
+    let dir = tempfile::tempdir().unwrap();
+
+    let out = Command::cargo_bin("hm")
+        .unwrap()
+        .arg("pipelines")
+        .arg("--dir")
+        .arg(dir.path())
+        .assert()
+        .success()
+        .get_output()
+        .stdout
+        .clone();
+
+    let v: serde_json::Value = serde_json::from_slice(&out).unwrap();
+    assert_eq!(v["pipelines"], serde_json::json!([]));
+}