[MM-18150] plugin panic trace should not be lost (#13559)

* Transit panic from debug to error

* Parse plugin's StdErr and output panic to the mlog.Error

* Add unit tests

* Change log test

* Remove buffer from logger

* Remove 'panic' string filter

* Change *Buffer to io.Writer

Co-authored-by: mattermod <mattermod@users.noreply.github.com>

mlog/log.go

@@ -144,6 +144,15 @@ func (l *Logger) StdLogWriter() io.Writer {
 	return &loggerWriter{f}
 }
 
+// StdErrPanicLogWriter returns a writer that can be hooked up to the output of a golang standard logger
+// all of the stderr will be interpreted as log entry.
+func (l *Logger) StdErrPanicLogWriter() io.Writer {
+	newLogger := *l
+	newLogger.zap = newLogger.zap.WithOptions(zap.AddCallerSkip(4), getStdLogOption())
+	f := newLogger.Error
+	return &panicLoggerWriter{f}
+}
+
 func (l *Logger) WithCallerSkip(skip int) *Logger {
 	newlogger := *l
 	newlogger.zap = newlogger.zap.WithOptions(zap.AddCallerSkip(skip))

mlog/stdlog.go

@@ -85,3 +85,13 @@ func (l *loggerWriter) Write(p []byte) (int, error) {
 	}
 	return len(p), nil
 }
+
+type panicLoggerWriter struct {
+	logFunc func(msg string, fields ...Field)
+}
+
+func (l *panicLoggerWriter) Write(p []byte) (int, error) {
+	trimmed := string(bytes.TrimSpace(p))
+	l.logFunc(trimmed)
+	return len(p), nil
+}

mlog/testing.go

@@ -4,6 +4,7 @@
 package mlog
 
 import (
+	"io"
 	"strings"
 	"testing"
 
@@ -23,9 +24,10 @@ func (tw *testingWriter) Write(b []byte) (int, error) {
 
 // NewTestingLogger creates a Logger that proxies logs through a testing interface.
 // This allows tests that spin up App instances to avoid spewing logs unless the test fails or -verbose is specified.
-func NewTestingLogger(tb testing.TB) *Logger {
+func NewTestingLogger(tb testing.TB, writer io.Writer) *Logger {
 	logWriter := &testingWriter{tb}
-	logWriterSync := zapcore.AddSync(logWriter)
+	multiWriter := io.MultiWriter(logWriter, writer)
+	logWriterSync := zapcore.AddSync(multiWriter)
 
 	testingLogger := &Logger{
 		consoleLevel: zap.NewAtomicLevelAt(getZapLevel("debug")),