Trim log source field to basename of file (#273)

This makes logs more readable and avoids leaking paths.

Before:
```
time=2023-03-22T16:38:30.238+01:00 level=INFO source=/Users/pieter.noordhuis/dev/bricks/bundle/phases/phase.go:30 msg="Phase: initialize"
time=2023-03-22T16:38:31.303+01:00 level=INFO source=/Users/pieter.noordhuis/dev/bricks/bundle/phases/phase.go:30 msg="Phase: build"
time=2023-03-22T16:38:31.303+01:00 level=INFO source=/Users/pieter.noordhuis/dev/bricks/bundle/phases/phase.go:30 msg="Phase: deploy"
```

After:
```
time=2023-03-22T17:02:47.290+01:00 level=INFO source=phase.go:30 msg="Phase: initialize"
time=2023-03-22T17:02:48.171+01:00 level=INFO source=phase.go:30 msg="Phase: build"
time=2023-03-22T17:02:48.171+01:00 level=INFO source=phase.go:30 msg="Phase: deploy"
```

cmd/root/logger.go

@@ -21,7 +21,10 @@ func initializeLogger(ctx context.Context, cmd *cobra.Command) (context.Context,
 	opts := slog.HandlerOptions{}
 	opts.Level = logLevel.Level()
 	opts.AddSource = true
-	opts.ReplaceAttr = log.ReplaceLevelAttr
+	opts.ReplaceAttr = log.ReplaceAttrFunctions{
+		log.ReplaceLevelAttr,
+		log.ReplaceSourceAttr,
+	}.ReplaceAttr
 
 	// Open the underlying log file if the user configured an actual file to log to.
 	err := logFile.Open()

libs/log/replace_attr.go

@@ -0,0 +1,18 @@
+package log
+
+import "golang.org/x/exp/slog"
+
+type ReplaceAttrFunction func(groups []string, a slog.Attr) slog.Attr
+
+// ReplaceAttrFunctions enables grouping functions that replace attributes
+// from a [slog.Handler]. Useful when multiple attributes need replacing.
+type ReplaceAttrFunctions []ReplaceAttrFunction
+
+// ReplaceAttr can be used as a value to pass to a handler to combine
+// multiple functions to replace attributes.
+func (fns ReplaceAttrFunctions) ReplaceAttr(groups []string, a slog.Attr) slog.Attr {
+	for _, fn := range fns {
+		a = fn(groups, a)
+	}
+	return a
+}

libs/log/replace_attr_test.go

@@ -0,0 +1,32 @@
+package log
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"golang.org/x/exp/slog"
+)
+
+func testReplaceA(groups []string, a slog.Attr) slog.Attr {
+	if a.Key == "foo" {
+		return slog.Int("foo", int(a.Value.Int64())+1)
+	}
+	return a
+}
+
+func TestReplaceAttrGroup(t *testing.T) {
+	var foo, bar, out slog.Attr
+
+	fn := ReplaceAttrFunctions{
+		testReplaceA,
+		testReplaceA,
+	}
+
+	foo = slog.Int("foo", 0)
+	out = fn.ReplaceAttr([]string{}, foo)
+	assert.EqualValues(t, 2, out.Value.Int64())
+
+	bar = slog.Int("bar", 0)
+	out = fn.ReplaceAttr([]string{}, bar)
+	assert.EqualValues(t, 0, out.Value.Int64())
+}

libs/log/source.go

@@ -0,0 +1,17 @@
+package log
+
+import (
+	"path/filepath"
+
+	"golang.org/x/exp/slog"
+)
+
+// ReplaceSourceAttr rewrites the source attribute to include only the file's basename.
+func ReplaceSourceAttr(groups []string, a slog.Attr) slog.Attr {
+	if a.Key != slog.SourceKey {
+		return a
+	}
+
+	a.Value = slog.StringValue(filepath.Base(a.Value.String()))
+	return a
+}

libs/log/source_test.go

@@ -0,0 +1,20 @@
+package log
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"golang.org/x/exp/slog"
+)
+
+func TestReplaceSourceAttrSourceKey(t *testing.T) {
+	attr := slog.String(slog.SourceKey, "bricks/bundle/phases/phase.go:30")
+	out := ReplaceSourceAttr([]string{}, attr)
+	assert.Equal(t, "phase.go:30", out.Value.String())
+}
+
+func TestReplaceSourceAttrOtherKey(t *testing.T) {
+	attr := slog.String("foo", "bar")
+	out := ReplaceSourceAttr([]string{}, attr)
+	assert.Equal(t, attr, out)
+}