Improve error for labs projects that do not provide labs.yml

cmd/labs/project/fetcher.go

@@ -151,6 +151,14 @@ func (f *fetcher) loadRemoteProjectDefinition(cmd *cobra.Command, version string
 	var err error
 	if !offlineInstall {
 		raw, err = github.ReadFileFromRef(ctx, "databrickslabs", f.name, version, "labs.yml")
+		// Most repositories in the databrickslabs org don't ship a labs.yml manifest
+		// (e.g. libraries published to package indexes), so a missing file means the
+		// project isn't installable through the CLI, not that the download failed.
+		if errors.Is(err, github.ErrNotFound) {
+			return nil, fmt.Errorf("databrickslabs/%s@%s does not provide labs.yml (%w); "+
+				"this project cannot be installed with the Databricks CLI, "+
+				"see https://github.com/databrickslabs/%s for instructions", f.name, version, err, f.name)
+		}
 		if err != nil {
 			return nil, fmt.Errorf("read labs.yml from GitHub: %w", err)
 		}

cmd/labs/project/fetcher_test.go

@@ -0,0 +1,30 @@
+package project_test
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/databricks/cli/cmd/labs/github"
+	"github.com/databricks/cli/internal/testcli"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestInstallerFailsForProjectWithoutLabsYml(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path == "/databrickslabs/blueprint/v0.3.15/labs.yml" {
+			w.WriteHeader(http.StatusNotFound)
+			return
+		}
+		t.Logf("Requested: %s", r.URL.Path)
+		t.FailNow()
+	}))
+	defer server.Close()
+	ctx := installerContext(t, server)
+
+	r := testcli.NewRunner(t, ctx, "labs", "install", "blueprint")
+	_, _, err := r.Run()
+	assert.ErrorIs(t, err, github.ErrNotFound)
+	assert.ErrorContains(t, err, "databrickslabs/blueprint@v0.3.15 does not provide labs.yml")
+	assert.ErrorContains(t, err, "cannot be installed with the Databricks CLI")
+}