feat: support SCP-like parent URLs with relative submodules (#492)

[raza-khan0108]

Support SCP-like Parent URLs with Relative Submodules

Closes #492

📝 Problem

When a parent repository uses an SCP-like Git URL (e.g., git@github.com:org/repo.git) and a submodule is configured with a relative path (e.g., ../other/submodule.git), ResolveSubmoduleURL previously converted the resolved endpoint into a standard SSH protocol URL (ssh://git@github.com/org/other/submodule.git).

While ssh://... is a valid protocol, converting an SCP-like URL into an ssh:// URL causes Git over SSH to request an absolute path on the remote server (/org/other/submodule.git starting from /) instead of a relative path (org/other/submodule.git relative to the login user's home directory or Git root). This breaks submodule cloning on standard and self-hosted Git SSH servers (e.g., GitLab, Gitea, standard SSH git accounts) and alters the user's configured protocol style.

---

💡 Proposed Solution

This PR implements step 4 of the proposed solution in #492 by preserving SCP-like syntax when resolving submodule URLs:

1. Detects whether the input parentURL lacks a URL scheme (!strings.Contains(parentURL, "://")).
2. Introduces a reconstructSCP helper function to format a transport.Endpoint struct back into standard SCP syntax (user@host:path or user@host:port:path) without injecting a leading slash into the remote repository path.
3. Updates existing unit test expectations and introduces new test cases covering SCP-like URLs without user components and with IP addresses.

---

🛠️ Key Changes

git/git.go

• Added reconstructSCP(ep *transport.Endpoint) string: Formats endpoint components into SCP syntax while trimming leading slashes on the remote path.
• Updated ResolveSubmoduleURL: Checks if parentURL is an SCP-like URL. If true, returns reconstructSCP(parentEP) instead of .String().

git/git_test.go

• Updated expectations for existing SCP test cases (scpRelativeSibling, scpRelativeChild, scpMultiLevelUp, scpWithPort) from ssh://... to git@github.com:....
• Added scpNoUserRelativeSibling: Verifies SCP URLs without a user component (github.com:org/deps/lib.git).
• Added scpIPAddressRelativeSibling: Verifies SCP URLs using IP addresses and deploy users (deploy@192.168.1.50:repos/deps/lib.git).

---

🧪 Verification & Examples

Parent URL	Submodule Path	Previous Resolution	New Resolution
git@github.com:org/main.git	../deps/lib.git	ssh://git@github.com/org/deps/lib.git ❌	git@github.com:org/deps/lib.git ✅
git@github.com:2222:org/main.git	../deps/lib.git	ssh://git@github.com:2222/org/deps/lib.git ❌	git@github.com:2222:org/deps/lib.git ✅
github.com:org/main.git	../deps/lib.git	ssh://github.com/org/deps/lib.git ❌	github.com:org/deps/lib.git ✅

---

✅ Checklist

• Code compiles and adheres to coding standards
• Unit tests updated and new test cases added for SCP resolution
• Tested against multi-level and custom-port SCP URLs
• Documentation and walkthrough updated

[Copilot]

Pull request overview

This PR updates ResolveSubmoduleURL to preserve SCP-like Git URL syntax when resolving relative submodule URLs, avoiding conversion to ssh://... which can change remote path semantics and break submodule cloning on some SSH servers.

Changes:

• Added reconstructSCP(*transport.Endpoint) to format resolved endpoints back into SCP-like syntax.
• Updated ResolveSubmoduleURL to return SCP-like output for scheme-less parent URLs.
• Updated and expanded unit tests to expect SCP-like outputs and cover additional SCP input variants (no user, IP address).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
git/git.go	Adds SCP reconstruction helper and changes ResolveSubmoduleURL output formatting for scheme-less parent URLs.
git/git_test.go	Updates SCP-related expectations and adds new SCP-oriented test cases.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.