add docker-agent.yaml config autodiscovery

Author: joshbarrington

pkg/config/resolve.go

@@ -142,8 +142,36 @@ func singleSource(key string, source Source) Sources {
 	return Sources{key: source}
 }
 
+// autodiscoverConfigFile checks the current working directory for a
+// docker-agent.yaml or docker-agent.yml file. It returns the absolute
+// path of the first match found, or "" if neither file exists.
+var autodiscoverConfigNames = []string{"docker-agent.yaml", "docker-agent.yml"}
+
+func autodiscoverConfigFile() string {
+	wd, err := os.Getwd()
+	if err != nil {
+		return ""
+	}
+	for _, name := range autodiscoverConfigNames {
+		path := filepath.Join(wd, name)
+		if fileExists(path) {
+			slog.Debug("Auto-discovered agent config", "path", path)
+			return path
+		}
+	}
+	return ""
+}
+
 // resolve resolves an agent reference, handling aliases and defaults
 func resolve(agentFilename string) (string, error) {
+	// When no agent file is specified, try to auto-discover a config file
+	// in the current directory before falling back to the embedded default.
+	if agentFilename == "" {
+		if discovered := autodiscoverConfigFile(); discovered != "" {
+			agentFilename = discovered
+		}
+	}
+
 	agentFilename = cmp.Or(agentFilename, "default")
 
 	// Try to resolve as an alias first

pkg/config/resolve_test.go

@@ -89,12 +89,96 @@ func TestResolveAgentFile_EmptyIsDefault(t *testing.T) {
 	home := t.TempDir()
 	t.Setenv("HOME", home)
 
+	// Ensure no docker-agent.yaml in the working directory
+	t.Chdir(t.TempDir())
+
+	resolved, err := resolve("")
+
+	require.NoError(t, err)
+	assert.Equal(t, "default", resolved)
+}
+
+func TestResolveAgentFile_AutodiscoverYaml(t *testing.T) {
+	home := t.TempDir()
+	t.Setenv("HOME", home)
+
+	dir := t.TempDir()
+	configFile := filepath.Join(dir, "docker-agent.yaml")
+	require.NoError(t, os.WriteFile(configFile, []byte(`version: "1"`), 0o644))
+	t.Chdir(dir)
+
+	resolved, err := resolve("")
+
+	require.NoError(t, err)
+	assert.Equal(t, configFile, resolved)
+}
+
+func TestResolveAgentFile_AutodiscoverYml(t *testing.T) {
+	home := t.TempDir()
+	t.Setenv("HOME", home)
+
+	dir := t.TempDir()
+	configFile := filepath.Join(dir, "docker-agent.yml")
+	require.NoError(t, os.WriteFile(configFile, []byte(`version: "1"`), 0o644))
+	t.Chdir(dir)
+
+	resolved, err := resolve("")
+
+	require.NoError(t, err)
+	assert.Equal(t, configFile, resolved)
+}
+
+func TestResolveAgentFile_AutodiscoverYamlTakesPrecedenceOverYml(t *testing.T) {
+	home := t.TempDir()
+	t.Setenv("HOME", home)
+
+	dir := t.TempDir()
+	primaryConfig := filepath.Join(dir, "docker-agent.yaml")
+	secondaryConfig := filepath.Join(dir, "docker-agent.yml")
+	require.NoError(t, os.WriteFile(primaryConfig, []byte(`version: "1"`), 0o644))
+	require.NoError(t, os.WriteFile(secondaryConfig, []byte(`version: "1"`), 0o644))
+	t.Chdir(dir)
+
 	resolved, err := resolve("")
 
+	require.NoError(t, err)
+	assert.Equal(t, primaryConfig, resolved)
+}
+
+func TestResolveAgentFile_AutodiscoverIgnoredWhenExplicitArg(t *testing.T) {
+	home := t.TempDir()
+	t.Setenv("HOME", home)
+
+	dir := t.TempDir()
+	// Place a docker-agent.yaml in cwd
+	require.NoError(t, os.WriteFile(filepath.Join(dir, "docker-agent.yaml"), []byte(`version: "1"`), 0o644))
+	t.Chdir(dir)
+
+	// Explicitly passing "default" should not trigger autodiscovery
+	resolved, err := resolve("default")
+
 	require.NoError(t, err)
 	assert.Equal(t, "default", resolved)
 }
 
+func TestResolveAgentFile_AutodiscoverIgnoredWhenExplicitFile(t *testing.T) {
+	home := t.TempDir()
+	t.Setenv("HOME", home)
+
+	dir := t.TempDir()
+	// Place a docker-agent.yaml in cwd
+	require.NoError(t, os.WriteFile(filepath.Join(dir, "docker-agent.yaml"), []byte(`version: "1"`), 0o644))
+	// Place an explicit agent file
+	explicitFile := filepath.Join(dir, "my-agent.yaml")
+	require.NoError(t, os.WriteFile(explicitFile, []byte(`version: "1"`), 0o644))
+	t.Chdir(dir)
+
+	resolved, err := resolve(explicitFile)
+
+	require.NoError(t, err)
+	assert.Equal(t, explicitFile, resolved)
+}
+
 func TestResolveAgentFile_DefaultIsDefault(t *testing.T) {
 	home := t.TempDir()
 	t.Setenv("HOME", home)