logger: add a dedicated QML logging Singleton

- adds log.info/error/debug/warn/fatal
- adds ability to write logs to any file
- add CLI options in addition to env to set log levels

core/cmd/dms/commands_common.go

@@ -26,6 +26,17 @@ var runCmd = &cobra.Command{
 	Run: func(cmd *cobra.Command, args []string) {
 		daemon, _ := cmd.Flags().GetBool("daemon")
 		session, _ := cmd.Flags().GetBool("session")
+		if v, _ := cmd.Flags().GetString("log-level"); v != "" {
+			if err := os.Setenv("DMS_LOG_LEVEL", v); err != nil {
+				log.Fatalf("Failed to set DMS_LOG_LEVEL: %v", err)
+			}
+		}
+		if v, _ := cmd.Flags().GetString("log-file"); v != "" {
+			if err := os.Setenv("DMS_LOG_FILE", v); err != nil {
+				log.Fatalf("Failed to set DMS_LOG_FILE: %v", err)
+			}
+		}
+		log.ApplyEnvOverrides()
 		if daemon {
 			runShellDaemon(session)
 		} else {

core/cmd/dms/main.go

@@ -15,6 +15,8 @@ func init() {
 	runCmd.Flags().BoolP("daemon", "d", false, "Run in daemon mode")
 	runCmd.Flags().Bool("daemon-child", false, "Internal flag for daemon child process")
 	runCmd.Flags().Bool("session", false, "Session managed (like as a systemd unit)")
+	runCmd.Flags().String("log-level", "", "Log level: debug, info, warn, error, fatal (overrides DMS_LOG_LEVEL)")
+	runCmd.Flags().String("log-file", "", "Append logs to this file in addition to stderr (overrides DMS_LOG_FILE)")
 	runCmd.Flags().MarkHidden("daemon-child")
 
 	greeterCmd.AddCommand(greeterInstallCmd, greeterSyncCmd, greeterEnableCmd, greeterStatusCmd, greeterUninstallCmd)

core/cmd/dms/main_distro.go

@@ -15,6 +15,8 @@ func init() {
 	runCmd.Flags().BoolP("daemon", "d", false, "Run in daemon mode")
 	runCmd.Flags().Bool("daemon-child", false, "Internal flag for daemon child process")
 	runCmd.Flags().Bool("session", false, "Session managed (like as a systemd unit)")
+	runCmd.Flags().String("log-level", "", "Log level: debug, info, warn, error, fatal (overrides DMS_LOG_LEVEL)")
+	runCmd.Flags().String("log-file", "", "Append logs to this file in addition to stderr (overrides DMS_LOG_FILE)")
 	runCmd.Flags().MarkHidden("daemon-child")
 
 	greeterCmd.AddCommand(greeterInstallCmd, greeterSyncCmd, greeterEnableCmd, greeterStatusCmd, greeterUninstallCmd)

core/cmd/dms/shell.go

@@ -80,6 +80,16 @@ func getRuntimeDir() string {
 	return os.TempDir()
 }
 
+func appendLogEnv(env []string) []string {
+	if v := os.Getenv("DMS_LOG_LEVEL"); v != "" {
+		env = append(env, "DMS_LOG_LEVEL="+v)
+	}
+	if v := os.Getenv("DMS_LOG_FILE"); v != "" {
+		env = append(env, "DMS_LOG_FILE="+v)
+	}
+	return env
+}
+
 func hasSystemdRun() bool {
 	_, err := exec.LookPath("systemd-run")
 	return err == nil
@@ -216,6 +226,8 @@ func runShellInteractive(session bool) {
 		cmd.Env = append(cmd.Env, "QT_QPA_PLATFORM=wayland;xcb")
 	}
 
+	cmd.Env = appendLogEnv(cmd.Env)
+
 	cmd.Stdin = os.Stdin
 	cmd.Stdout = os.Stdout
 	cmd.Stderr = os.Stderr
@@ -459,6 +471,8 @@ func runShellDaemon(session bool) {
 		cmd.Env = append(cmd.Env, "QT_QPA_PLATFORM=wayland;xcb")
 	}
 
+	cmd.Env = appendLogEnv(cmd.Env)
+
 	devNull, err := os.OpenFile("/dev/null", os.O_RDWR, 0)
 	if err != nil {
 		log.Fatalf("Error opening /dev/null: %v", err)

core/go.mod

@@ -66,12 +66,12 @@ require (
 	github.com/go-git/go-git/v6 v6.0.0-alpha.2
 	github.com/inconshreveable/mousetrap v1.1.0 // indirect
 	github.com/lucasb-eyer/go-colorful v1.4.0
-	github.com/mattn/go-isatty v0.0.22 // indirect
+	github.com/mattn/go-isatty v0.0.22
 	github.com/mattn/go-localereader v0.0.1 // indirect
 	github.com/mattn/go-runewidth v0.0.23 // indirect
 	github.com/muesli/ansi v0.0.0-20230316100256-276c6243b2f6 // indirect
 	github.com/muesli/cancelreader v0.2.2 // indirect
-	github.com/muesli/termenv v0.16.0 // indirect
+	github.com/muesli/termenv v0.16.0
 	github.com/pmezard/go-difflib v1.0.0 // indirect
 	github.com/rivo/uniseg v0.4.7 // indirect
 	github.com/spf13/afero v1.15.0

core/internal/log/log.go

@@ -1,12 +1,16 @@
 package log
 
 import (
+	"io"
 	"os"
+	"regexp"
 	"strings"
 	"sync"
 
 	"github.com/charmbracelet/lipgloss"
 	cblog "github.com/charmbracelet/log"
+	"github.com/mattn/go-isatty"
+	"github.com/muesli/termenv"
 )
 
 // Logger embeds the Charm Logger and adds Printf/Fatalf
@@ -21,8 +25,26 @@ func (l *Logger) Fatalf(format string, v ...any) { l.Logger.Fatalf(format, v...)
 var (
 	logger     *Logger
 	initLogger sync.Once
+
+	logMu     sync.Mutex
+	logFile   *os.File
+	logStderr io.Writer = os.Stderr
+
+	ansiRe = regexp.MustCompile(`\x1b\[[0-9;]*[a-zA-Z]`)
 )
 
+// ansiStripWriter strips ANSI escape sequences before forwarding to w. Used
+// for the file sink so colored stderr stays colored while the file stays plain.
+type ansiStripWriter struct{ w io.Writer }
+
+func (a *ansiStripWriter) Write(p []byte) (int, error) {
+	stripped := ansiRe.ReplaceAll(p, nil)
+	if _, err := a.w.Write(stripped); err != nil {
+		return 0, err
+	}
+	return len(p), nil
+}
+
 func parseLogLevel(level string) cblog.Level {
 	switch strings.ToLower(level) {
 	case "debug":
@@ -86,7 +108,7 @@ func GetLogger() *Logger {
 			SetString(" DEBUG").
 			Foreground(lipgloss.Color("4"))
 
-		base := cblog.New(os.Stderr)
+		base := cblog.New(logStderr)
 		base.SetStyles(styles)
 		base.SetReportTimestamp(false)
 
@@ -98,10 +120,85 @@ func GetLogger() *Logger {
 		base.SetPrefix(" go")
 
 		logger = &Logger{base}
+
+		if path := os.Getenv("DMS_LOG_FILE"); path != "" {
+			_ = SetLogFile(path)
+		}
 	})
 	return logger
 }
 
+// SetLevel updates the active log level. Accepts the same strings as
+// DMS_LOG_LEVEL. Unknown values default to info.
+func SetLevel(level string) {
+	GetLogger().SetLevel(parseLogLevel(level))
+}
+
+// SetLogFile makes the logger append to path in addition to stderr. Passing an
+// empty string detaches the file sink. Atomic per-line writes (≤PIPE_BUF) on
+// O_APPEND keep concurrent Go and QML writers from corrupting each other.
+//
+// Color handling: charmbracelet/log auto-detects color support from its
+// io.Writer, and io.MultiWriter doesn't pass that through, so we force the ANSI
+// profile when stderr is a TTY and route the file through ansiStripWriter so
+// the file stays plain while stderr keeps its colors.
+func SetLogFile(path string) error {
+	logMu.Lock()
+	defer logMu.Unlock()
+
+	if logFile != nil {
+		logFile.Close()
+		logFile = nil
+	}
+
+	l := GetLogger()
+	if path == "" {
+		l.SetOutput(logStderr)
+		applyColorProfile(l, logStderr)
+		return nil
+	}
+
+	f, err := os.OpenFile(path, os.O_WRONLY|os.O_APPEND|os.O_CREATE, 0o644)
+	if err != nil {
+		return err
+	}
+	logFile = f
+	out := io.MultiWriter(logStderr, &ansiStripWriter{w: f})
+	l.SetOutput(out)
+	applyColorProfile(l, logStderr)
+	return nil
+}
+
+// applyColorProfile forces the renderer's color profile to match what stderr
+// would produce on its own, undoing the auto-downgrade triggered by wrapping
+// stderr in a non-TTY writer (e.g. io.MultiWriter).
+func applyColorProfile(l *Logger, stderr io.Writer) {
+	f, ok := stderr.(*os.File)
+	if !ok {
+		l.SetColorProfile(termenv.Ascii)
+		return
+	}
+	if isatty.IsTerminal(f.Fd()) {
+		l.SetColorProfile(termenv.ANSI)
+		return
+	}
+	l.SetColorProfile(termenv.Ascii)
+}
+
+// ApplyEnvOverrides re-reads DMS_LOG_LEVEL and DMS_LOG_FILE and reconfigures
+// the singleton. Safe to call after CLI flags have rewritten the environment.
+func ApplyEnvOverrides() {
+	GetLogger()
+	if level := os.Getenv("DMS_LOG_LEVEL"); level != "" {
+		SetLevel(level)
+	}
+	if path := os.Getenv("DMS_LOG_FILE"); path != "" {
+		if err := SetLogFile(path); err != nil {
+			Warnf("Failed to open log file %q: %v", path, err)
+		}
+	}
+}
+
 // * Convenience wrappers
 
 func Debug(msg any, keyvals ...any)  { GetLogger().Debug(msg, keyvals...) }