feat: added slog adapter (#1173)

Unsure if this is even wanted however, this PR introduces an adapter
(originally from [here](https://github.com/robbert229/fxslog/tree/main))
to more easily use slog as the underlying logger implementation instead
of zap.


This covers: #1170

fxevent/slog.go

@@ -0,0 +1,279 @@
+// Copyright (c) 2021 Uber Technologies, Inc.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
+//go:build go1.21
+
+package fxevent
+
+import (
+	"context"
+	"log/slog"
+	"strconv"
+	"strings"
+)
+
+var _ Logger = (*SlogLogger)(nil)
+
+// SlogLogger an Fx event logger that logs events using a slog logger.
+type SlogLogger struct {
+	Logger *slog.Logger
+
+	ctx        context.Context
+	logLevel   slog.Level
+	errorLevel *slog.Level
+}
+
+// UseContext sets the context that will be used when logging to slog.
+func (l *SlogLogger) UseContext(ctx context.Context) {
+	l.ctx = ctx
+}
+
+// UseLogLevel sets the level of non-error logs emitted by Fx to level.
+func (l *SlogLogger) UseLogLevel(level slog.Level) {
+	l.logLevel = level
+}
+
+// UseErrorLevel sets the level of error logs emitted by Fx to level.
+func (l *SlogLogger) UseErrorLevel(level slog.Level) {
+	l.errorLevel = &level
+}
+
+func (l *SlogLogger) filter(fields []any) []any {
+	filtered := []any{}
+
+	for _, field := range fields {
+		if field, ok := field.(slog.Attr); ok {
+			if _, ok := field.Value.Any().(slogFieldSkip); ok {
+				continue
+			}
+		}
+
+		filtered = append(filtered, field)
+	}
+
+	return filtered
+}
+
+func (l *SlogLogger) logEvent(msg string, fields ...any) {
+	l.Logger.Log(l.ctx, l.logLevel, msg, l.filter(fields)...)
+}
+
+func (l *SlogLogger) logError(msg string, fields ...any) {
+	lvl := slog.LevelError
+	if l.errorLevel != nil {
+		lvl = *l.errorLevel
+	}
+
+	l.Logger.Log(l.ctx, lvl, msg, l.filter(fields)...)
+}
+
+// LogEvent logs the given event to the provided Zap logger.
+func (l *SlogLogger) LogEvent(event Event) {
+	switch e := event.(type) {
+	case *OnStartExecuting:
+		l.logEvent("OnStart hook executing",
+			slog.String("callee", e.FunctionName),
+			slog.String("caller", e.CallerName),
+		)
+	case *OnStartExecuted:
+		if e.Err != nil {
+			l.logError("OnStart hook failed",
+				slog.String("callee", e.FunctionName),
+				slog.String("caller", e.CallerName),
+				slogErr(e.Err),
+			)
+		} else {
+			l.logEvent("OnStart hook executed",
+				slog.String("callee", e.FunctionName),
+				slog.String("caller", e.CallerName),
+				slog.String("runtime", e.Runtime.String()),
+			)
+		}
+	case *OnStopExecuting:
+		l.logEvent("OnStop hook executing",
+			slog.String("callee", e.FunctionName),
+			slog.String("caller", e.CallerName),
+		)
+	case *OnStopExecuted:
+		if e.Err != nil {
+			l.logError("OnStop hook failed",
+				slog.String("callee", e.FunctionName),
+				slog.String("caller", e.CallerName),
+				slogErr(e.Err),
+			)
+		} else {
+			l.logEvent("OnStop hook executed",
+				slog.String("callee", e.FunctionName),
+				slog.String("caller", e.CallerName),
+				slog.String("runtime", e.Runtime.String()),
+			)
+		}
+	case *Supplied:
+		if e.Err != nil {
+			l.logError("error encountered while applying options",
+				slog.String("type", e.TypeName),
+				slogStrings("moduletrace", e.ModuleTrace),
+				slogStrings("stacktrace", e.StackTrace),
+				slogMaybeModuleField(e.ModuleName),
+				slogErr(e.Err))
+		} else {
+			l.logEvent("supplied",
+				slog.String("type", e.TypeName),
+				slogStrings("stacktrace", e.StackTrace),
+				slogStrings("moduletrace", e.ModuleTrace),
+				slogMaybeModuleField(e.ModuleName),
+			)
+		}
+	case *Provided:
+		for _, rtype := range e.OutputTypeNames {
+			l.logEvent("provided",
+				slog.String("constructor", e.ConstructorName),
+				slogStrings("stacktrace", e.StackTrace),
+				slogStrings("moduletrace", e.ModuleTrace),
+				slogMaybeModuleField(e.ModuleName),
+				slog.String("type", rtype),
+				slogMaybeBool("private", e.Private),
+			)
+		}
+		if e.Err != nil {
+			l.logError("error encountered while applying options",
+				slogMaybeModuleField(e.ModuleName),
+				slogStrings("stacktrace", e.StackTrace),
+				slogStrings("moduletrace", e.ModuleTrace),
+				slogErr(e.Err))
+		}
+	case *Replaced:
+		for _, rtype := range e.OutputTypeNames {
+			l.logEvent("replaced",
+				slogStrings("stacktrace", e.StackTrace),
+				slogStrings("moduletrace", e.ModuleTrace),
+				slogMaybeModuleField(e.ModuleName),
+				slog.String("type", rtype),
+			)
+		}
+		if e.Err != nil {
+			l.logError("error encountered while replacing",
+				slogStrings("stacktrace", e.StackTrace),
+				slogStrings("moduletrace", e.ModuleTrace),
+				slogMaybeModuleField(e.ModuleName),
+				slogErr(e.Err))
+		}
+	case *Decorated:
+		for _, rtype := range e.OutputTypeNames {
+			l.logEvent("decorated",
+				slog.String("decorator", e.DecoratorName),
+				slogStrings("stacktrace", e.StackTrace),
+				slogStrings("moduletrace", e.ModuleTrace),
+				slogMaybeModuleField(e.ModuleName),
+				slog.String("type", rtype),
+			)
+		}
+		if e.Err != nil {
+			l.logError("error encountered while applying options",
+				slogStrings("stacktrace", e.StackTrace),
+				slogStrings("moduletrace", e.ModuleTrace),
+				slogMaybeModuleField(e.ModuleName),
+				slogErr(e.Err))
+		}
+	case *Run:
+		if e.Err != nil {
+			l.logError("error returned",
+				slog.String("name", e.Name),
+				slog.String("kind", e.Kind),
+				slogMaybeModuleField(e.ModuleName),
+				slogErr(e.Err),
+			)
+		} else {
+			l.logEvent("run",
+				slog.String("name", e.Name),
+				slog.String("kind", e.Kind),
+				slogMaybeModuleField(e.ModuleName),
+			)
+		}
+	case *Invoking:
+		// Do not log stack as it will make logs hard to read.
+		l.logEvent("invoking",
+			slog.String("function", e.FunctionName),
+			slogMaybeModuleField(e.ModuleName),
+		)
+	case *Invoked:
+		if e.Err != nil {
+			l.logError("invoke failed",
+				slogErr(e.Err),
+				slog.String("stack", e.Trace),
+				slog.String("function", e.FunctionName),
+				slogMaybeModuleField(e.ModuleName),
+			)
+		}
+	case *Stopping:
+		l.logEvent("received signal",
+			slog.String("signal", strings.ToUpper(e.Signal.String())))
+	case *Stopped:
+		if e.Err != nil {
+			l.logError("stop failed", slogErr(e.Err))
+		}
+	case *RollingBack:
+		l.logError("start failed, rolling back", slogErr(e.StartErr))
+	case *RolledBack:
+		if e.Err != nil {
+			l.logError("rollback failed", slogErr(e.Err))
+		}
+	case *Started:
+		if e.Err != nil {
+			l.logError("start failed", slogErr(e.Err))
+		} else {
+			l.logEvent("started")
+		}
+	case *LoggerInitialized:
+		if e.Err != nil {
+			l.logError("custom logger initialization failed", slogErr(e.Err))
+		} else {
+			l.logEvent("initialized custom fxevent.Logger", slog.String("function", e.ConstructorName))
+		}
+	}
+}
+
+type slogFieldSkip struct{}
+
+func slogMaybeModuleField(name string) slog.Attr {
+	if len(name) == 0 {
+		return slog.Any("module", slogFieldSkip{})
+	}
+	return slog.String("module", name)
+}
+
+func slogMaybeBool(name string, b bool) slog.Attr {
+	if !b {
+		return slog.Any(name, slogFieldSkip{})
+	}
+	return slog.Bool(name, true)
+}
+
+func slogErr(err error) slog.Attr {
+	return slog.String("error", err.Error())
+}
+
+func slogStrings(key string, str []string) slog.Attr {
+	attrs := make([]any, len(str))
+	for i, val := range str {
+		attrs[i] = slog.String(strconv.Itoa(i), val)
+	}
+	return slog.Group(key, attrs...)
+}