[PATCH 1/5] git-son: add command to create independent child repositories

["Evan Haque via GitGitGadget" <gitgitgadget@gmail.com>]

From: Evan Haque <evanhaque1@gmail.com>

Introduce git-son, a new porcelain command that creates an independent
child repository inside the current working tree. Unlike submodules,
the child is not tracked by the parent; instead its directory is added
to the parent's .gitignore and a "parent" remote is configured in the
child pointing back to the parent's origin URL or local path.

This gives users a lightweight way to spin off a related repository
that knows where it came from without the coupling that submodules
impose.

The command supports two optional flags:

  --inherit    fetch the parent's history into the child at creation
  --branch     check out a specific parent branch (requires --inherit)

Assisted-by: Claude Opus 4.6
Signed-off-by: Evan Haque <evanhaque1@gmail.com>
---
 git-son.sh | 97 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 97 insertions(+)
 create mode 100755 git-son.sh

diff --git a/git-son.sh b/git-son.sh
new file mode 100755
index 0000000000..a212c7b69f
--- /dev/null
+++ b/git-son.sh
@@ -0,0 +1,97 @@
+#!/bin/sh
+#
+# git-son: create an independent child repository that knows its parent
+#
+
+SUBDIRECTORY_OK='Yes'
+OPTIONS_SPEC='git son [options] <name>
+--
+inherit    fetch parent history into the son
+branch=    start the son from a specific parent branch
+'
+
+. git-sh-setup
+require_work_tree
+cd_to_toplevel
+
+inherit=
+branch=
+while test $# -gt 0
+do
+	case "$1" in
+	--inherit)
+		inherit=1 ;;
+	--branch)
+		shift
+		branch="$1" ;;
+	--)
+		shift; break ;;
+	-*)
+		usage ;;
+	*)
+		break ;;
+	esac
+	shift
+done
+
+name="$1"
+test -n "$name" || usage
+
+if test -n "$branch" && test -z "$inherit"
+then
+	die "fatal: --branch requires --inherit"
+fi
+
+parent_dir="$(pwd)"
+parent_remote="$(git remote get-url origin 2>/dev/null)" || parent_remote=
+
+if test -e "$name"
+then
+	die "fatal: '$name' already exists"
+fi
+
+mkdir "$name" || die "fatal: could not create directory '$name'"
+
+if ! echo "$name/" >> "$parent_dir/.gitignore" 2>/dev/null
+then
+	rm -rf "$name"
+	die "fatal: could not update .gitignore"
+fi
+
+cd "$name" || die "fatal: could not enter directory '$name'"
+
+if ! git init
+then
+	rm -rf "$parent_dir/$name"
+	die "fatal: could not initialize repository in '$name'"
+fi
+
+if test -n "$parent_remote"
+then
+	git remote add parent "$parent_remote"
+else
+	git remote add parent "$parent_dir"
+fi
+
+if test -n "$inherit"
+then
+	git fetch parent || die "fatal: could not fetch from parent"
+	if test -n "$branch"
+	then
+		git checkout -b "$branch" "parent/$branch" ||
+			die "fatal: could not checkout branch '$branch'"
+	else
+		git checkout -b main parent/HEAD 2>/dev/null ||
+			git checkout -b main "parent/$(git remote show parent | sed -n 's/.*HEAD branch: //p')" 2>/dev/null ||
+			echo "warning: could not determine parent HEAD, starting empty"
+	fi
+else
+	echo "# $name" > README.md
+	git add README.md
+	git commit -q -m "Initial commit"
+fi
+
+echo ""
+echo "Created son repository '$name'"
+echo "  parent: ${parent_remote:-$parent_dir}"
+echo "  inherit: ${inherit:-no}"
-- 
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