Moving mlog to corelibs (#16915)

* Moving mlog to corelibs

* Regenerating app layers

* Fix golangci-lint problem

* Fixing golangci-lint errors

* Renaming from corelibs to shared

* Renaming from corelibs to shared

* Fixing import

* Fixing merge problems

* Fixing build

shared/mlog/default.go

@@ -0,0 +1,95 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package mlog
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"os"
+
+	"github.com/mattermost/logr"
+)
+
+// defaultLog manually encodes the log to STDERR, providing a basic, default logging implementation
+// before mlog is fully configured.
+func defaultLog(level, msg string, fields ...Field) {
+	log := struct {
+		Level   string  `json:"level"`
+		Message string  `json:"msg"`
+		Fields  []Field `json:"fields,omitempty"`
+	}{
+		level,
+		msg,
+		fields,
+	}
+
+	if b, err := json.Marshal(log); err != nil {
+		fmt.Fprintf(os.Stderr, `{"level":"error","msg":"failed to encode log message"}%s`, "\n")
+	} else {
+		fmt.Fprintf(os.Stderr, "%s\n", b)
+	}
+}
+
+func defaultDebugLog(msg string, fields ...Field) {
+	defaultLog("debug", msg, fields...)
+}
+
+func defaultInfoLog(msg string, fields ...Field) {
+	defaultLog("info", msg, fields...)
+}
+
+func defaultWarnLog(msg string, fields ...Field) {
+	defaultLog("warn", msg, fields...)
+}
+
+func defaultErrorLog(msg string, fields ...Field) {
+	defaultLog("error", msg, fields...)
+}
+
+func defaultCriticalLog(msg string, fields ...Field) {
+	// We map critical to error in zap, so be consistent.
+	defaultLog("error", msg, fields...)
+}
+
+func defaultCustomLog(lvl LogLevel, msg string, fields ...Field) {
+	// custom log levels are only output once log targets are configured.
+}
+
+func defaultCustomMultiLog(lvl []LogLevel, msg string, fields ...Field) {
+	// custom log levels are only output once log targets are configured.
+}
+
+func defaultFlush(ctx context.Context) error {
+	return nil
+}
+
+func defaultAdvancedConfig(cfg LogTargetCfg) error {
+	// mlog.ConfigAdvancedConfig should not be called until default
+	// logger is replaced with mlog.Logger instance.
+	return errors.New("cannot config advanced logging on default logger")
+}
+
+func defaultAdvancedShutdown(ctx context.Context) error {
+	return nil
+}
+
+func defaultAddTarget(targets ...logr.Target) error {
+	// mlog.AddTarget should not be called until default
+	// logger is replaced with mlog.Logger instance.
+	return errors.New("cannot AddTarget on default logger")
+}
+
+func defaultRemoveTargets(ctx context.Context, f func(TargetInfo) bool) error {
+	// mlog.RemoveTargets should not be called until default
+	// logger is replaced with mlog.Logger instance.
+	return errors.New("cannot RemoveTargets on default logger")
+}
+
+func defaultEnableMetrics(collector logr.MetricsCollector) error {
+	// mlog.EnableMetrics should not be called until default
+	// logger is replaced with mlog.Logger instance.
+	return errors.New("cannot EnableMetrics on default logger")
+}