toggledlog: assume command of color handling

We want to use colored error messages also outside of main,
so let's handle it in the logging package.

The fatal logger now automatically prints red.

1 files changed, 38 insertions, 7 deletions

diff --git a/internal/toggledlog/log.go b/internal/toggledlog/log.go
index 23d7347..30fab18 100644
--- a/internal/toggledlog/log.go
+++ b/internal/toggledlog/log.go
@@ -5,6 +5,8 @@ import (
 	"fmt"
 	"log"
 	"os"
+
+	"golang.org/x/crypto/ssh/terminal"
 )
 
 const (
@@ -12,6 +14,10 @@ const (
 	wpanicMsg   = "-wpanic turns this warning into a panic: "
 )
 
+// Escape sequences for terminal colors. These will be empty strings if stdout
+// is not a terminal.
+var ColorReset, ColorGrey, ColorRed, ColorGreen, ColorYellow string
+
 func JSONDump(obj interface{}) string {
 	b, err := json.MarshalIndent(obj, "", "\t")
 	if err != nil {
@@ -27,6 +33,10 @@ type toggledLogger struct {
 	Enabled bool
 	// Panic after logging a message, useful in regression tests
 	Wpanic bool
+	// Private prefix and postfix are used for coloring
+	prefix  string
+	postfix string
+
 	*log.Logger
 }
 
@@ -34,7 +44,7 @@ func (l *toggledLogger) Printf(format string, v ...interface{}) {
 	if !l.Enabled {
 		return
 	}
-	l.Logger.Printf(format, v...)
+	l.Logger.Printf(l.prefix + fmt.Sprintf(format, v...) + l.postfix)
 	if l.Wpanic {
 		l.Logger.Panic(wpanicMsg + fmt.Sprintf(format, v...))
 	}
@@ -43,9 +53,9 @@ func (l *toggledLogger) Println(v ...interface{}) {
 	if !l.Enabled {
 		return
 	}
-	l.Logger.Println(v...)
+	l.Logger.Println(l.prefix + fmt.Sprint(v...) + l.postfix)
 	if l.Wpanic {
-		l.Logger.Panic(wpanicMsg + fmt.Sprintln(v...))
+		l.Logger.Panic(wpanicMsg + fmt.Sprint(v...))
 	}
 }
 
@@ -65,8 +75,29 @@ var Warn *toggledLogger
 var Fatal *toggledLogger
 
 func init() {
-	Debug = &toggledLogger{false, false, log.New(os.Stdout, "", 0)}
-	Info = &toggledLogger{true, false, log.New(os.Stdout, "", 0)}
-	Warn = &toggledLogger{true, false, log.New(os.Stderr, "", 0)}
-	Fatal = &toggledLogger{true, false, log.New(os.Stderr, "", 0)}
+	if terminal.IsTerminal(int(os.Stdout.Fd())) {
+		ColorReset = "\033[0m"
+		ColorGrey = "\033[2m"
+		ColorRed = "\033[31m"
+		ColorGreen = "\033[32m"
+		ColorYellow = "\033[33m"
+	}
+
+	Debug = &toggledLogger{
+		Logger: log.New(os.Stdout, "", 0),
+	}
+	Info = &toggledLogger{
+		Enabled: true,
+		Logger:  log.New(os.Stdout, "", 0),
+	}
+	Warn = &toggledLogger{
+		Enabled: true,
+		Logger:  log.New(os.Stderr, "", 0),
+	}
+	Fatal = &toggledLogger{
+		Enabled: true,
+		Logger:  log.New(os.Stderr, "", 0),
+		prefix:  ColorRed,
+		postfix: ColorReset,
+	}
 }