refactor(logging): replace the logrus backend with log/slog (#1304)

Log through `log/slog`, with a console `slog.Handler` that writes the text the runner has always written (sorted `key=value` fields on a plain stream, a colored prefix on a terminal), so nothing changes for users. I compared its output byte for byte with logrus's `TextFormatter` over plain, colored, timestamped and caller cases.

Why not `slog.TextHandler`: its output differs from what users and their log parsers see today, and `ReplaceAttr` cannot close the gap.
- level is `WARN` where logrus wrote `warning`, and time has milliseconds and no quotes
- fields keep call order instead of being sorted
- the caller is one `source=` key, where the runner writes `func=` and `file=` (reshaped by `callPrettyfier`), and `ReplaceAttr` returns a single attribute
- no colored prefix on a terminal
- no hook to rewrite a whole formatted line, which the process-wide secret masking relies on

Libraries that log through logrus's global logger (the workflow model, the Docker client) are forwarded to the process-wide logger, so they keep following its level, format and secret masking. This is why logrus stays in `go.mod`.

Stacked on https://gitea.com/gitea/runner/pulls/1303.

Assisted-by: Codet
Co-authored-by: bircni <[email protected]>
Reviewed-on: https://gitea.com/gitea/runner/pulls/1304
Reviewed-by: bircni <[email protected]>

act/common/logging/console_test.go

@@ -0,0 +1,78 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package logging
+
+import (
+	"bytes"
+	"errors"
+	"log/slog"
+	"runtime"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func consoleLine(t *testing.T, opts TextOptions, terminal, reportCaller bool, build func(*Logger)) string {
+	t.Helper()
+	var out bytes.Buffer
+	c := newConsole(&out)
+	c.opts, c.terminal, c.reportCaller = opts, terminal, reportCaller
+	c.level.Set(slog.LevelDebug)
+	build(New(NewSlogHandler(&consoleHandler{c: c})))
+	return out.String()
+}
+
+func TestConsolePlain(t *testing.T) {
+	line := consoleLine(t, TextOptions{DisableTimestamp: true}, false, false, func(l *Logger) {
+		l.With("job", "build x", "n", 3).WithError(errors.New("boom")).Warnf("hello world")
+		l.With("msg", "clash", "empty", "").Info("")
+	})
+	assert.Equal(t, "level=warning msg=\"hello world\" error=boom job=\"build x\" n=3\n"+
+		"level=info empty= fields.msg=clash\n", line)
+}
+
+func TestConsolePlainTimeFilterAndCaller(t *testing.T) {
+	opts := TextOptions{
+		CallerPrettyfier: func(f *runtime.Frame) (string, string) {
+			return "[fn]", "[" + strings.TrimPrefix(f.Function, "x") + "]"
+		},
+		Filter: func(b []byte) []byte { return bytes.ReplaceAll(b, []byte("secret"), []byte("***")) },
+	}
+	line := consoleLine(t, opts, false, true, func(l *Logger) { l.With("k", "secret").Debugf("a secret") })
+	assert.Regexp(t, `^time="[^"]+" level=debug msg="a \*\*\*" func="\[fn\]" file="\[.*TestConsolePlainTimeFilterAndCaller[^"]*\]" k=\*\*\*\n$`, line)
+}
+
+func TestConsoleColored(t *testing.T) {
+	line := consoleLine(t, TextOptions{DisableTimestamp: true}, true, false, func(l *Logger) {
+		l.With("job", "j").Warn("careful")
+	})
+	assert.Equal(t, "\x1b[33mWARN\x1b[0m "+"careful"+strings.Repeat(" ", 44-len("careful"))+"  \x1b[33mjob\x1b[0m=j\n", line)
+
+	full := consoleLine(t, TextOptions{FullTimestamp: true}, true, false, func(l *Logger) { l.Error("bad") })
+	assert.Regexp(t, `^\x1b\[31mERRO\x1b\[0m\[\d{4}-\d\d-\d\dT[^\]]+\] bad`, full)
+
+	elapsed := consoleLine(t, TextOptions{}, true, false, func(l *Logger) { l.Info("x") })
+	assert.Regexp(t, `^\x1b\[36mINFO\x1b\[0m\[\d{4}\] x`, elapsed)
+
+	plain := consoleLine(t, TextOptions{DisableColors: true, DisableTimestamp: true}, true, false, func(l *Logger) { l.Info("x") })
+	assert.Equal(t, "level=info msg=x\n", plain)
+}
+
+func TestConsoleLevelAndOutput(t *testing.T) {
+	var out bytes.Buffer
+	c := newConsole(&out)
+	h := &consoleHandler{c: c}
+	assert.False(t, h.Enabled(t.Context(), slog.LevelDebug)) // info unless raised
+	c.level.Set(slog.LevelError)
+	assert.False(t, h.Enabled(t.Context(), slog.LevelWarn))
+	assert.True(t, h.Enabled(t.Context(), slog.LevelError))
+
+	rec := slog.NewRecord(time.Unix(0, 0), slog.LevelError, "m", 0)
+	rec.AddAttrs(slog.String("c", "3"))
+	require.NoError(t, h.WithAttrs([]slog.Attr{slog.Int("a", 1)}).Handle(t.Context(), rec))
+	assert.Contains(t, out.String(), "a=1 c=3")
+}