config: add branch description support

config/branch.go

@@ -2,6 +2,7 @@ package config
 
 import (
 	"errors"
+	"strings"
 
 	"github.com/go-git/go-git/v5/plumbing"
 	format "github.com/go-git/go-git/v5/plumbing/format/config"
@@ -26,6 +27,12 @@ type Branch struct {
 	// "true" and "interactive".  "false" is undocumented and
 	// typically represented by the non-existence of this field
 	Rebase string
+	// Description explains what the branch is for.
+	// Multi-line explanations may be used.
+	//
+	// Original git command to edit:
+	//	git branch --edit-description
+	Description string
 
 	raw *format.Subsection
 }
@@ -75,16 +82,42 @@ func (b *Branch) marshal() *format.Subsection {
 		b.raw.SetOption(rebaseKey, b.Rebase)
 	}
 
+	if b.Description == "" {
+		b.raw.RemoveOption(descriptionKey)
+	} else {
+		desc := quoteDescription(b.Description)
+		b.raw.SetOption(descriptionKey, desc)
+	}
+
 	return b.raw
 }
 
+// hack to trigger conditional quoting in the
+// plumbing/format/config/Encoder.encodeOptions
+//
+// Current Encoder implementation uses Go %q format if value contains a backslash character,
+// which is not consistent with reference git implementation.
+// git just replaces newline characters with \n, while Encoder prints them directly.
+// Until value quoting fix, we should escape description value by replacing newline characters with \n.
+func quoteDescription(desc string) string {
+	return strings.ReplaceAll(desc, "\n", `\n`)
+}
+
 func (b *Branch) unmarshal(s *format.Subsection) error {
 	b.raw = s
 
 	b.Name = b.raw.Name
 	b.Remote = b.raw.Options.Get(remoteSection)
 	b.Merge = plumbing.ReferenceName(b.raw.Options.Get(mergeKey))
 	b.Rebase = b.raw.Options.Get(rebaseKey)
+	b.Description = unquoteDescription(b.raw.Options.Get(descriptionKey))
 
 	return b.Validate()
 }
+
+// hack to enable conditional quoting in the
+// plumbing/format/config/Encoder.encodeOptions
+// goto quoteDescription for details.
+func unquoteDescription(desc string) string {
+	return strings.ReplaceAll(desc, `\n`, "\n")
+}

config/config.go

@@ -247,6 +247,7 @@ const (
 	rebaseKey        = "rebase"
 	nameKey          = "name"
 	emailKey         = "email"
+	descriptionKey   = "description"
 	defaultBranchKey = "defaultBranch"
 
 	// DefaultPackWindow holds the number of previous objects used to

config/config_test.go

@@ -50,6 +50,7 @@ func (s *ConfigSuite) TestUnmarshal(c *C) {
 [branch "master"]
 		remote = origin
 		merge = refs/heads/master
+		description = "Add support for branch description.\\n\\nEdit branch description: git branch --edit-description\\n"
 [init]
 		defaultBranch = main
 [url "ssh://git@github.com/"]
@@ -86,6 +87,7 @@ func (s *ConfigSuite) TestUnmarshal(c *C) {
 	c.Assert(cfg.Submodules["qux"].Branch, Equals, "bar")
 	c.Assert(cfg.Branches["master"].Remote, Equals, "origin")
 	c.Assert(cfg.Branches["master"].Merge, Equals, plumbing.ReferenceName("refs/heads/master"))
+	c.Assert(cfg.Branches["master"].Description, Equals, "Add support for branch description.\n\nEdit branch description: git branch --edit-description\n")
 	c.Assert(cfg.Init.DefaultBranch, Equals, "main")
 }
 
@@ -111,6 +113,7 @@ func (s *ConfigSuite) TestMarshal(c *C) {
 [branch "master"]
 	remote = origin
 	merge = refs/heads/master
+	description = "Add support for branch description.\\n\\nEdit branch description: git branch --edit-description\\n"
 [url "ssh://git@github.com/"]
 	insteadOf = https://github.com/
 [init]
@@ -149,9 +152,10 @@ func (s *ConfigSuite) TestMarshal(c *C) {
 	}
 
 	cfg.Branches["master"] = &Branch{
-		Name:   "master",
-		Remote: "origin",
-		Merge:  "refs/heads/master",
+		Name:        "master",
+		Remote:      "origin",
+		Merge:       "refs/heads/master",
+		Description: "Add support for branch description.\n\nEdit branch description: git branch --edit-description\n",
 	}
 
 	cfg.URLs["ssh://git@github.com/"] = &URL{
@@ -364,4 +368,5 @@ func (s *ConfigSuite) TestRemoveUrlOptions(c *C) {
 	if strings.Contains(string(buf), "url") {
 		c.Fatal("conifg should not contain any url sections")
 	}
+	c.Assert(err, IsNil)
 }