git son: add command to create independent child repositories

[Evandabest]

Motivation

When spinning off a new project that is related to an existing repository, there is no built-in way to create a child repository that maintains a link back to its parent without the tight coupling of submodules. Submodules pin the child to a specific commit and require the parent to track the child in its index, which is too heavyweight when the child is meant to be fully independent.

The typical workflow today is manual: git init, git remote add, update .gitignore — three steps that are easy to forget or get wrong. git son automates this and establishes a lightweight convention for the parent-child relationship: a remote named parent in the child, and nothing in the parent except an ignore rule.

Summary

This series introduces git son, a new porcelain command that creates an independent child repository inside the current working tree. Unlike a submodule, the child is not tracked by the parent; instead, its subdirectory is added to the parent's .gitignore. The child is configured at creation time with a remote named parent pointing back to the parent repository's origin URL (or local path if no origin exists), making the lineage explicit and recoverable via standard Git commands.

Changes

• git-son.sh: new shell script implementing the command, supporting --inherit to fetch parent history at creation time and --branch <branch> (requires --inherit) to check out a specific parent branch
• git-son registered in command-list.txt as mainporcelain
• git-son.sh added to SCRIPT_SH in Makefile and to scripts_sh in meson.build
• Documentation/git-son.adoc: new man page covering synopsis, option descriptions, and worked examples
• Documentation/meson.build: git-son.adoc added to the manpage build list
• t/t5151-son.sh: new test script covering basic creation, parent remote configuration, .gitignore update, idempotency failure, flag validation, and
  --inherit with a bare remote

Details

The key design property is independence: the child is a fully self-contained repository with no entry in the parent's index. The parent remote is the only artifact linking the two, which means git fetch parent and git log parent/<branch> work as expected from within the child without any special tooling.

The --branch flag is intentionally restricted to --inherit mode. Without fetching, there is no remote-tracking branch to check out from, so accepting --branch alone would be misleading; the command dies with a clear diagnostic in that case.

When no origin URL is available in the parent, the parent remote is set to the parent's absolute local path. This covers the common case of repositories that have never been pushed to a remote.

Testing

t/t5151-son.sh covers the following scenarios:

• Basic child repository creation (directory exists, .git present)
• parent remote is correctly recorded in the child
• Child directory is appended to the parent's .gitignore
• Child starts with exactly one initial commit when --inherit is not used
• Command fails without leaving a directory when the target already exists
• --branch without --inherit is rejected before any filesystem changes
• --inherit fetches parent history and the remote-tracking branch is reachable in the child

[gitgitgadget]

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[gitgitgadget]

There are issues in commit b627ec5:
Add git-son: create independent child repositories

• Commit checks stopped - the message is too short
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[gitgitgadget]

There are issues in commit 1b98825:
git-son: register in Makefile and meson build system

• Commit checks stopped - the message is too short
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[gitgitgadget]

There are issues in commit 21680fc:
git-son: add to command list as mainporcelain

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[gitgitgadget]

There are issues in commit 52c738e:
git-son: add documentation

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[gitgitgadget]

There are issues in commit 4bb623d:
git-son: add tests

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[gitgitgadget]

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[gitgitgadget]

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There are issues in commit 46fba44:
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[gitgitgadget]

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