[exp] slog: add NewLogLogger

[Jonathan Amsterdam (Gerrit)]

Jonathan Amsterdam submitted this change.

View Change

1 is the latest approved patch-set.
The change was submitted with unreviewed changes in the following files:

```
The name of the file: slog/logger.go
Insertions: 4, Deletions: 2.

@@ -52,6 +52,7 @@
 	}
 	var pc uintptr
 	if w.capturePC {
+		// skip [runtime.Callers, callerPC, w.Write, Logger.Output, log.Print]
 		pc = callerPC(5)
 	}
 
@@ -146,8 +147,9 @@
 	return l.Handler().Enabled(l.ctx, level)
 }
 
-// NewLogLogger returns a log.Logger whose output becomes the message
-// of the given Handler, at the given level.
+// NewLogLogger returns a new log.Logger such that each call to its Output method
+// dispatches a Record to the specified handler. The logger acts as a bridge from
+// the older log API to newer structured logging handlers.
 func NewLogLogger(h Handler, level Level) *log.Logger {
 	return log.New(&handlerWriter{h, level, true}, "", 0)
 }
```

Approvals: Alan Donovan: Looks good to me, approved Russ Cox: Looks good to me, approved Gopher Robot: TryBots succeeded Jonathan Amsterdam: Run TryBots

slog: add NewLogLogger

Add a function that creates a log.Logger that writes to a Handler.

This generalizes what we already do for the default log.Logger.

Change-Id: I7ebfba3404b6fe9960eeb7dccd5385d1166a4bcb
Reviewed-on: https://go-review.googlesource.com/c/exp/+/465356
Reviewed-by: Alan Donovan <adon...@google.com>
Reviewed-by: Russ Cox <r...@golang.org>
Run-TryBot: Jonathan Amsterdam <j...@google.com>
TryBot-Result: Gopher Robot <go...@golang.org>
---
M slog/logger.go
M slog/logger_test.go
2 files changed, 42 insertions(+), 6 deletions(-)

diff --git a/slog/logger.go b/slog/logger.go
index 79d5bdd..cf77f40 100644
--- a/slog/logger.go
+++ b/slog/logger.go
@@ -32,7 +32,8 @@
 	// This can occur with SetDefault(Default()).
 	// See TestSetDefault.
 	if _, ok := l.Handler().(*defaultHandler); !ok {
-		log.SetOutput(&handlerWriter{l.Handler(), log.Flags()})
+		capturePC := log.Flags()&(log.Lshortfile|log.Llongfile) != 0
+		log.SetOutput(&handlerWriter{l.Handler(), LevelInfo, capturePC})
 		log.SetFlags(0) // we want just the log message, no time or location
 	}
 }
@@ -40,16 +41,18 @@
 // handlerWriter is an io.Writer that calls a Handler.
 // It is used to link the default log.Logger to the default slog.Logger.
 type handlerWriter struct {
-	h     Handler
-	flags int
+	h         Handler
+	level     Level
+	capturePC bool
 }
 
 func (w *handlerWriter) Write(buf []byte) (int, error) {
-	if !w.h.Enabled(nil, LevelInfo) {
+	if !w.h.Enabled(nil, w.level) {
 		return 0, nil
 	}
 	var pc uintptr
-	if w.flags&(log.Lshortfile|log.Llongfile) != 0 {
+	if w.capturePC {
+		// skip [runtime.Callers, callerPC, w.Write, Logger.Output, log.Print]
 		pc = callerPC(5)
 	}
 
@@ -58,7 +61,7 @@
 	if len(buf) > 0 && buf[len(buf)-1] == '\n' {
 		buf = buf[:len(buf)-1]
 	}
-	r := NewRecord(time.Now(), LevelInfo, string(buf), pc, nil)
+	r := NewRecord(time.Now(), w.level, string(buf), pc, nil)
 	return origLen, w.h.Handle(r)
 }
 
@@ -144,6 +147,13 @@
 	return l.Handler().Enabled(l.ctx, level)
 }
 
+// NewLogLogger returns a new log.Logger such that each call to its Output method
+// dispatches a Record to the specified handler. The logger acts as a bridge from
+// the older log API to newer structured logging handlers.
+func NewLogLogger(h Handler, level Level) *log.Logger {
+	return log.New(&handlerWriter{h, level, true}, "", 0)
+}
+
 // Log emits a log record with the current time and the given level and message.
 // The Record's Attrs consist of the Logger's attributes followed by
 // the Attrs specified by args.
diff --git a/slog/logger_test.go b/slog/logger_test.go
index c7529eb..0729ca7 100644
--- a/slog/logger_test.go
+++ b/slog/logger_test.go
@@ -408,6 +408,14 @@
 	checkContext(l4)
 }
 
+func TestNewLogLogger(t *testing.T) {
+	var buf bytes.Buffer
+	h := NewTextHandler(&buf)
+	ll := NewLogLogger(h, LevelWarn)
+	ll.Print("hello")
+	checkLogOutput(t, buf.String(), "time="+timeRE+` level=WARN msg=hello`)
+}
+
 func checkLogOutput(t *testing.T, got, wantRegexp string) {
 	t.Helper()
 	got = clean(got)

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Gerrit-Project: exp

Gerrit-Branch: master

Gerrit-Change-Id: I7ebfba3404b6fe9960eeb7dccd5385d1166a4bcb

Gerrit-Change-Number: 465356

Gerrit-PatchSet: 3

Gerrit-Owner: Jonathan Amsterdam <j...@google.com>

Gerrit-Reviewer: Alan Donovan <adon...@google.com>

Gerrit-Reviewer: Gopher Robot <go...@golang.org>

Gerrit-Reviewer: Jonathan Amsterdam <j...@google.com>

Gerrit-Reviewer: Russ Cox <r...@golang.org>

Gerrit-MessageType: merged