Intorduce "config edit-ini" sub command to help maintaining INI config file (#35735)

Ref: #32669. Helps addressing
https://gitea.com/gitea/helm-chart/issues/356.

cmd/config.go

@@ -0,0 +1,156 @@
+// Copyright 2025 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package cmd
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"os"
+
+	"code.gitea.io/gitea/modules/setting"
+
+	"github.com/urfave/cli/v3"
+)
+
+func cmdConfig() *cli.Command {
+	subcmdConfigEditIni := &cli.Command{
+		Name:  "edit-ini",
+		Usage: "Load an existing INI file, apply environment variables, keep specified keys, and output to a new INI file.",
+		Description: `
+Help users to edit the Gitea configuration INI file.
+
+# Keep Specified Keys
+
+If you need to re-create the configuration file with only a subset of keys,
+you can provide an INI template file for the kept keys and use the "--config-keep-keys" flag.
+For example, if a helm chart needs to reset the settings and only keep SECRET_KEY,
+it can use a template file (only keys take effect, values are ignored):
+
+  [security]
+  SECRET_KEY=
+
+$ ./gitea config edit-ini --config app-old.ini --config-keep-keys app-keys.ini --out app-new.ini
+
+# Map Environment Variables to INI Configuration
+
+Environment variables of the form "GITEA__section_name__KEY_NAME"
+will be mapped to the ini section "[section_name]" and the key
+"KEY_NAME" with the value as provided.
+
+Environment variables of the form "GITEA__section_name__KEY_NAME__FILE"
+will be mapped to the ini section "[section_name]" and the key
+"KEY_NAME" with the value loaded from the specified file.
+
+Environment variable keys can only contain characters "0-9A-Z_",
+if a section or key name contains dot ".", it needs to be escaped as _0x2E_.
+For example, to apply this config:
+
+	[git.config]
+	foo.bar=val
+
+$ export GITEA__git_0x2E_config__foo_0x2E_bar=val
+
+# Put All Together
+
+$ ./gitea config edit-ini --config app.ini --config-keep-keys app-keys.ini --apply-env {--in-place|--out app-new.ini}
+`,
+		Flags: []cli.Flag{
+			// "--config" flag is provided by global flags, and this flag is also used by "environment-to-ini" script wrapper
+			// "--in-place" is also used by "environment-to-ini" script wrapper for its old behavior: always overwrite the existing config file
+			&cli.BoolFlag{
+				Name:  "in-place",
+				Usage: "Output to the same config file as input. This flag will be ignored if --out is set.",
+			},
+			&cli.StringFlag{
+				Name:  "config-keep-keys",
+				Usage: "An INI template file containing keys for keeping. Only the keys defined in the INI template will be kept from old config. If not set, all keys will be kept.",
+			},
+			&cli.BoolFlag{
+				Name:  "apply-env",
+				Usage: "Apply all GITEA__* variables from the environment to the config.",
+			},
+			&cli.StringFlag{
+				Name:  "out",
+				Usage: "Destination config file to write to.",
+			},
+		},
+		Action: runConfigEditIni,
+	}
+
+	return &cli.Command{
+		Name:  "config",
+		Usage: "Manage Gitea configuration",
+		Commands: []*cli.Command{
+			subcmdConfigEditIni,
+		},
+	}
+}
+
+func runConfigEditIni(_ context.Context, c *cli.Command) error {
+	// the config system may change the environment variables, so get a copy first, to be used later
+	env := append([]string{}, os.Environ()...)
+
+	// don't use the guessed setting.CustomConf, instead, require the user to provide --config explicitly
+	if !c.IsSet("config") {
+		return errors.New("flag is required but not set: --config")
+	}
+	configFileIn := c.String("config")
+
+	cfgIn, err := setting.NewConfigProviderFromFile(configFileIn)
+	if err != nil {
+		return fmt.Errorf("failed to load config file %q: %v", configFileIn, err)
+	}
+
+	// determine output config file: use "--out" flag or use "--in-place" flag to overwrite input file
+	inPlace := c.Bool("in-place")
+	configFileOut := c.String("out")
+	if configFileOut == "" {
+		if !inPlace {
+			return errors.New("either --in-place or --out must be specified")
+		}
+		configFileOut = configFileIn // in-place edit
+	}
+
+	needWriteOut := configFileOut != configFileIn
+
+	cfgOut := cfgIn
+	configKeepKeys := c.String("config-keep-keys")
+	if configKeepKeys != "" {
+		needWriteOut = true
+		cfgOut, err = setting.NewConfigProviderFromFile(configKeepKeys)
+		if err != nil {
+			return fmt.Errorf("failed to load config-keep-keys template file %q: %v", configKeepKeys, err)
+		}
+
+		for _, secOut := range cfgOut.Sections() {
+			for _, keyOut := range secOut.Keys() {
+				secIn := cfgIn.Section(secOut.Name())
+				keyIn := setting.ConfigSectionKey(secIn, keyOut.Name())
+				if keyIn != nil {
+					keyOut.SetValue(keyIn.String())
+				} else {
+					secOut.DeleteKey(keyOut.Name())
+				}
+			}
+			if len(secOut.Keys()) == 0 {
+				cfgOut.DeleteSection(secOut.Name())
+			}
+		}
+	}
+
+	if c.Bool("apply-env") {
+		if setting.EnvironmentToConfig(cfgOut, env) {
+			needWriteOut = true
+		}
+	}
+
+	if needWriteOut {
+		err = cfgOut.SaveTo(configFileOut)
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}