VCS Provider Reference¶

The VCS provider layer is an abstraction that lets sase commands work transparently with both Git and Mercurial repositories. Every command that touches version control — commit, amend, ace, axe, revert, restore — delegates to a provider interface rather than calling VCS commands directly.

Both Git and Mercurial are first-class supported. The same sase workflows (creating commits, amending, syncing, mailing/pushing for review, reverting, restoring) work identically regardless of which VCS backs the repository.

Plugin Architecture¶

VCS providers are implemented as pluggy plugins. The core sase package only bundles the BareGitPlugin (for plain git repositories). Additional VCS backends are installed as separate packages:

Package	Plugin	Description
`sase` (core)	`BareGitPlugin`	Standard git operations (bundled)
`sase-github`	`GitHubPlugin`	Git + GitHub CLI (`gh`) for PR operations
`sase-google`	`HgPlugin`	Mercurial with `sase_hg_*` helper commands

Install optional providers via pip:

pip install sase-github   # GitHub PR support
pip install sase-google       # Mercurial support

Plugins register themselves via the sase_vcs entry point group. The plugin manager loads all registered plugins and dispatches VCS operations through pluggy's firstresult=True hook system — the first plugin that returns a non-None result wins.

Hook Specification¶

All VCS operations are defined in VCSHookSpec (src/sase/vcs_provider/_hookspec.py). Each method is prefixed with vcs_ and returns tuple[bool, str | None] (success flag and optional output). Plugins implement only the hooks they support; unsupported operations return None and are skipped.

The hooks are organized into several groups:

Core operations — vcs_checkout, vcs_diff, vcs_diff_revision, vcs_apply_patch, vcs_apply_patches, vcs_add_remove, vcs_clean_workspace, vcs_commit, vcs_amend, vcs_rename_branch, vcs_rebase, vcs_archive, vcs_prune, vcs_stash_and_clean
Optional core — vcs_resolve_revision, vcs_show_revision, vcs_diff_with_untracked, vcs_committed_diff, vcs_get_default_parent_revision, vcs_file_at_revision
Sync operations — vcs_sync_workspace, vcs_is_sync_in_progress, vcs_get_conflicted_files, vcs_continue_sync, vcs_abort_sync
Commit dispatch — vcs_create_commit, vcs_create_proposal, vcs_create_pull_request (the three commit workflow methods dispatched by CommitWorkflow), plus vcs_finalize_commit (replays idempotent post-commit work — bead amend, push-with-retry — when sase commit --resume finishes a workflow whose dispatch was interrupted by a merge conflict; plugins that cannot safely replay finalization can leave this unimplemented, and the workflow will only replay its tracking steps). See commit_workflows.md.
VCS-agnostic operations — vcs_abandon_change, vcs_prepare_description_for_reword, vcs_get_change_url
Info and review hooks — vcs_reword, vcs_reword_add_tag, vcs_get_description, vcs_get_branch_name, vcs_get_cl_number, vcs_get_workspace_name, vcs_has_local_changes, vcs_get_bug_number, vcs_mail, vcs_fix, vcs_upload, vcs_find_reviewers, vcs_rewind
Branch naming hooks — vcs_derive_branch_name, vcs_derive_branch_name_with_suffix (compute branch names from ChangeSpec names), vcs_can_rename_branch (check if branch renaming is supported)
Classification hooks — vcs_detect_repo_type (detect VCS markers like .hg/ or .git/) and vcs_classify_repo (classify git repos by remote URL, e.g. GitHub vs bare)

Disabling Plugins¶

Set SASE_DISABLE_PLUGINS to disable all plugin groups, or SASE_DISABLE_PLUGIN_VCS to disable VCS plugins specifically. See docs/configuration.md for details.

Provider Selection¶

Sase uses a 3-tier resolution strategy to decide which VCS provider to use. The first tier that returns a concrete provider wins.

Tier 1: Environment Variable¶

The SASE_VCS_PROVIDER environment variable takes highest priority.

# Force git provider
SASE_VCS_PROVIDER=git sase commit my_feature

# Force hg provider
SASE_VCS_PROVIDER=hg sase ace

# Defer to next tier
SASE_VCS_PROVIDER=auto sase commit my_feature

The --vcs-provider CLI flag on sase ace and sase axe sets this variable internally:

# Equivalent to SASE_VCS_PROVIDER=git sase ace
sase ace --vcs-provider git

# Same for axe
sase axe --vcs-provider hg start

Valid values: git, hg, auto.

Tier 2: Configuration File¶

If the environment variable is not set (or is unset entirely — not "auto"), sase checks ~/.config/sase/sase.yml:

vcs_provider:
  provider: git # or "hg" or "auto"

Setting provider: auto defers to auto-detection (Tier 3).

Note: If the environment variable is set to "auto", the config file is skipped entirely and auto-detection runs directly. Only an unset environment variable consults the config.

Tier 3: Auto-Detection¶

If neither the environment variable nor config file specifies a provider, sase walks up the directory tree from the current working directory looking for .hg/ or .git/ directories. The first one found determines the provider.

.hg/ found first → Mercurial provider ("hg")
.git/ found first → Git provider. If a GitHub remote is detected, uses "github" (requires sase-github plugin); otherwise uses "bare_git".
.git/ found with a hosted remote (e.g., GitHub) but no VCS plugin claims the repo → falls back to "bare_git". This preserves baseline commit capability even without provider-specific plugins like sase-github.
Neither found → Error: VCSProviderNotFoundError

The detect_vcs() function returns one of three values: "github", "bare_git", or "hg". A convenience function detect_vcs_family() collapses "github" and "bare_git" into "git" for contexts that only care about the VCS family.

Per-Command VCS Usage¶

`sase commit`¶

Dispatches to one of three VCS methods (create_commit, create_proposal, create_pull_request) via the CommitWorkflow orchestrator. See docs/commit_workflows.md for the full workflow reference.

Key VCS operations used:

Operation	Git	Mercurial
Bug number	Returns empty string (not applicable)	`sase_hg_branch_bug` command
Workspace name	`git config --get remote.origin.url` (extracts repo name)	`workspace_name` command
Create commit	`git add` + `git commit` + `git push`	`hg commit --name "<name>" --logfile "<logfile>"`
Create proposal	Save diff + `git reset --hard` + `git clean -fd`	`sase_hg_clean <diff_name>`
Create PR	Branch + commit + push + `gh pr create`	Not supported natively
Change URL	`gh pr view --json url -q .url`	`http://cl/<branch_number>`

`sase ace` TUI Actions¶

The ace TUI provides interactive actions that use VCS operations:

Sync (`S` key)¶

Syncs the workspace with the remote repository.

Step	Git	Mercurial
Checkout	`git checkout <name>`	`sase_hg_update <name>`
Sync	`git fetch origin` + `git rebase origin/<default_branch>`	`sase_hg_sync`

The git sync auto-detects the default branch (main/master) via git symbolic-ref refs/remotes/origin/HEAD.

Mail (`m` key)¶

Pushes changes for review. The flow differs significantly between providers.

Git flow:

Display branch name and commit description
Prompt user to confirm push
git push -u origin <branch>
Check if PR exists via gh pr view
If no PR: gh pr create --fill with an agent info footer appended to the PR body (model and agent name from agent_meta.json, if available)
Update ChangeSpec with PR URL

Mercurial flow:

Prompt for reviewers (1 or 2, or @ to run p4 findreviewers -c <cl_number>)
Modify CL description with reviewer tags and startblock configuration
Reword CL description via sase_hg_reword
Prompt user to confirm mail
hg mail -r <revision>

Show Diff (`d` key)¶

Displays the diff for a ChangeSpec. Uses diff() for uncommitted changes or diff_revision() for committed revisions.

Type	Git	Mercurial
Uncommitted	`git diff HEAD`	`hg diff`
Revision	`git diff origin/<default>...<rev>` (merge-base)	`hg diff -c <rev>`

Revert (`X` key / status change to "Reverted")¶

Reverts a ChangeSpec by saving its diff and pruning the revision.

Save diff to ~/.sase/reverted/<name>.diff via diff_revision()
Prune revision via prune()
Update status to "Reverted"

Operation	Git	Mercurial
Prune	`git branch -D <revision>`	`sase_hg_prune <revision>`

Restore (status change from "Reverted" to "WIP"/"Drafted")¶

Restores a previously reverted ChangeSpec.

Checkout parent or default branch via checkout()
Apply stashed diff via apply_patch()
Run sase commit to re-create the commit

Operation	Git	Mercurial
Checkout	`git checkout <target>`	`sase_hg_update <target>`
Apply patch	`git apply <path>`	`hg import --no-commit <path>`

Archive (status change to "Archived")¶

Archives a ChangeSpec by saving the diff, archiving the revision, and updating status.

Checkout the CL via checkout()
Save diff to ~/.sase/archived/<name>.diff
Archive revision via archive()

Operation	Git	Mercurial
Archive	`git tag archive/<name> <name>` + `git branch -D <name>`	`sase_hg_archive <name>`

Reword (`w` key)¶

Amends the commit message without changing code.

Operation	Git	Mercurial
Reword	`git commit --amend -m <description>`	`sase_hg_reword <description>`

The Mercurial provider applies ANSI-C escape quoting to the description (escaping backslashes, single quotes, newlines, tabs, carriage returns) because sase_hg_reword uses $'...' shell quoting internally.

`sase axe`¶

Background daemon that periodically checks ChangeSpecs and runs hooks. Uses VCS operations for:

Hook running — Workspace checkout and sync before running hooks
Mentor checks — Checking for changes via has_local_changes()
Workspace sync — Periodic sync via sync_workspace()

The --vcs-provider flag works identically to sase ace.

`sase revert`¶

Standalone command to revert a ChangeSpec. Performs the same operations as the ace TUI revert action:

Save diff via diff_revision() to ~/.sase/reverted/<name>.diff
Prune revision via prune()
Update status to "Reverted"

`sase restore`¶

Standalone command to restore a reverted ChangeSpec:

Checkout parent (or default branch) via checkout()
Apply saved diff via apply_patch() from ~/.sase/reverted/ or ~/.sase/archived/
Run sase commit to re-create the commit

Git Provider Details¶

The Git provider is split into two plugins: BareGitPlugin (bundled with core sase) handles standard git commands, while GitHubPlugin (from the sase-github package) adds GitHub CLI (gh) support for PR operations.

Branch Naming¶

Git branch names match ChangeSpec names exactly — no prefix stripping or underscore-to-hyphen conversion. Two VCS hooks control branch name derivation:

vcs_derive_branch_name() — returns the base branch name (ChangeSpec name without __<N> suffix)
vcs_derive_branch_name_with_suffix() — returns the full branch name including suffix

Immutable branch aliases: When a provider cannot rename branches (e.g., GitHub with open PRs), sase persists branch aliases in ~/.sase/projects/<project>/branch_map.json. This maps the current ChangeSpec name to the actual git branch name. The vcs_can_rename_branch() hook tells the system whether renaming is possible — GitHub returns False for branches with open PRs, so alias mappings are used instead of git branch -m.

Branch Management¶

Creates feature branches with git checkout -b <name> during commit
Renames branches with git branch -m <new_name> (when vcs_can_rename_branch() returns True)
Falls back to branch alias mapping when renaming is not possible
Current branch detected via git rev-parse --abbrev-ref HEAD

PR Integration¶

All PR operations use the gh CLI:

Create PR: gh pr create --fill (auto-fills title/body from commit)
View PR: gh pr view --json url -q .url
Get PR number: gh pr view --json number -q .number

GitHub Plugin Scope¶

The GitHub plugin covers the core git/PR lifecycle by combining GitHub-specific hooks with the shared git provider mixins. It can classify GitHub remotes, create and inspect PRs, preserve immutable branch aliases for open PRs, resolve workspace references such as #gh:<ref>, and submit merged PRs through gh pr merge.

It does not currently provide the richer Google/Mercurial-specific automation surface. In particular, GitHub PRs do not get plugin-supplied default ChangeSpec hooks, metahooks, mentor profiles, PR tags, or a provider-specific precommit/fix command unless users configure those in sase.yml. Reviewer-comment polling and comment-response automation are not enabled for GitHub PR URLs, reviewer discovery during mail preparation is not implemented, vcs_rewind has no GitHub backend, BUG values are left as provided, and the Google-only refresh/split workflows do not have GitHub equivalents.

These are plugin capability gaps, not core VCS limitations: ordinary git operations, diffing, branch management, commit/proposal/PR dispatch, conflict resume, and workspace setup are still provided by the shared git implementation.

Sync¶

git fetch origin
git rebase origin/<default_branch>

The default branch is auto-detected from git symbolic-ref refs/remotes/origin/HEAD, falling back to main.

Archive¶

Preserves commits via a tag before deleting the branch:

git tag archive/<name> <name>
git branch -D <name>

Diff¶

Uncommitted changes: git diff HEAD (falls back to git diff for empty repos)
Specific revision: git diff origin/<default>...<rev> (three-dot merge-base syntax, showing the full PR diff). Falls back to git diff <rev>~1 <rev> for edge cases (detached HEAD, orphan branches), then to git show for root commits.

Workspace Info¶

Repository name: Extracted from git config --get remote.origin.url (strips .git suffix), falls back to git rev-parse --show-toplevel basename
Local changes: git status --porcelain
Commit description: git log --format=%B -n1 <revision> (full) or git log --format=%s -n1 <revision> (short)

Tag Operations¶

Adding tags to commit descriptions:

git log --format=%B -n1 HEAD    # Read current message
git commit --amend -m "<msg>\n<tag>=<value>"    # Append tag

Mercurial Provider Details¶

The Mercurial provider is available via the sase-google package (pip install sase-google). It uses a combination of standard hg commands and sase_hg_* wrapper commands.

Core Commands¶

Operation	Command
Commit	`hg commit --name <name> --logfile <logfile>`
Amend	`sase_hg_amend [--no-upload] <note>`
Checkout	`sase_hg_update <revision>`
Sync	`sase_hg_sync`
Archive	`sase_hg_archive <revision>`
Prune	`sase_hg_prune <revision>`
Rename	`sase_hg_rename <new_name>`
Rebase	`sase_hg_rebase <branch> <new_parent>`
Reword	`sase_hg_reword <description>`
Add tag	`sase_hg_reword --add-tag <name> <value>`
Clean	`sase_hg_clean <diff_name>` (saves diff and cleans)

Branch and Workspace Info¶

Info	Command
Branch name	`branch_name`
CL number	`branch_number`
Bug number	`sase_hg_branch_bug`
Workspace name	`workspace_name`
Local changes	`branch_local_changes`

Description Management¶

Operation	Command
Full description	`cl_desc -r <revision>`
Short description	`cl_desc -s`

Review Operations¶

Operation	Command
Mail for review	`hg mail -r <revision>`
Find reviewers	`p4 findreviewers -c <cl_number>`
Upload	`hg upload tree`
Fix	`hg fix`

Diff and Patch¶

Operation	Command
Uncommitted diff	`hg diff`
Revision diff	`hg diff -c <revision>`
Apply patch	`hg import --no-commit <path>`
Rewind	`sase_hg_rewind <diff_paths>`

Change URL¶

CL URLs follow the pattern http://cl/<number>, where the number comes from branch_number.

Description Escaping¶

The prepare_description_for_reword() method escapes descriptions for sase_hg_reword's $'...' shell quoting:

\ → \\ (backslashes first)
' → \'
newline → \n
tab → \t
carriage return → \r

Diff Management¶

Sase maintains diff files in ~/.sase/ for tracking changes across operations.

Diff Storage Locations¶

Directory	Purpose	When Used
`~/.sase/diffs/<cl_name>-<timestamp>.diff`	Pre-commit/amend diff snapshots	Every commit and amend
`~/.sase/reverted/<name>.diff`	Stashed diff for reverted CLs	`sase revert` / ace revert action
`~/.sase/archived/<name>.diff`	Stashed diff for archived CLs	ace archive action

Patch Application¶

Provider	Apply Command
Git	`git apply <path>`
Mercurial	`hg import --no-commit <path>`

Multiple patches can be applied at once — both providers accept multiple paths in a single command.

Stash and Clean¶

The stash_and_clean() operation saves the current diff to a file and resets the workspace:

Provider	Steps
Git	`git diff HEAD` → write to file → `git reset --hard HEAD` → `git clean -fd`
Mercurial	`sase_hg_clean <diff_name>` (handles both steps internally)

Configuration Reference¶

Full `sase.yml` Example¶

# ~/.config/sase/sase.yml

vcs_provider:
  provider: auto # "git", "hg", or "auto" (default: "auto")

Environment Variable¶

# Override VCS provider for a single command
SASE_VCS_PROVIDER=git sase commit my_feature

# Set for the entire shell session
export SASE_VCS_PROVIDER=hg

CLI Flags¶

Available on sase ace and sase axe only:

sase ace --vcs-provider git
sase ace --vcs-provider hg
sase ace --vcs-provider auto

sase axe start --vcs-provider git

Valid values for all three methods: git, hg, auto.

Schema¶

The vcs_provider section in sase.yml is validated against the schema at ~/.config/sase/sase.schema.json:

{
  "vcs_provider": {
    "type": "object",
    "additionalProperties": false,
    "properties": {
      "provider": {
        "type": "string",
        "enum": ["git", "hg", "auto"],
        "default": "auto"
      }
    }
  }
}

Classification Hooks¶

VCS provider detection is pluggable via two classification hooks:

`vcs_detect_repo_type`¶

Checks for VCS markers in a directory (e.g., .hg/, .git/). Each plugin checks for its own marker and returns the VCS type name (e.g., "hg") or None. Used during auto-detection when walking up the directory tree.

`vcs_classify_repo`¶

For git repositories, further classifies by examining the remote URL. For example, the sase-github plugin claims repos with github.com URLs (returning "github"), while unclaimed repos fall through to the "bare_git" provider. This allows hosting-specific plugins to provide enhanced functionality (e.g., PR operations via gh CLI) without modifying the core.

Troubleshooting¶

"No VCS provider found" Error¶

Cause: Auto-detection could not find .hg/ or .git/ in the current directory or any parent, and no explicit provider was configured.

Fix: Either run sase from within a VCS-managed directory, or set the provider explicitly:

SASE_VCS_PROVIDER=git sase commit my_feature

Git: `gh` CLI Not Installed¶

PR operations (get_change_url, mail, get_cl_number) require the GitHub CLI. Without it, these operations will fail with a "command not found" error.

Symptoms:

sase commit completes but reports "Failed to retrieve change URL"
sase ace mail action fails with "gh pr create failed"
No PR URL shown after commit

Fix: Install the GitHub CLI and authenticate:

# macOS
brew install gh

# Then authenticate
gh auth login

Mercurial: Plugin Not Installed¶

The Mercurial provider requires the sase-google package. Without it, hg repositories will not be detected.

Symptoms:

Auto-detection does not recognize .hg/ directories
"No VCS provider found" error in hg repositories

Fix: Install the Mercurial plugin:

pip install sase-google

Mercurial: `sase_hg_*` Commands Not Found¶

The Mercurial provider depends on sase_hg_* wrapper commands. If these are not in your PATH, operations will fail.

Symptoms:

"sase_hg_amend command not found"
"sase_hg_sync command not found"
Any core hg operation failing with "command not found"

Fix: Ensure your PATH includes the directory containing the sase_hg_* scripts.

Auto-Detection Picks Wrong Provider in Nested Repos¶

If you have nested repositories (e.g., a git repo inside an hg workspace), auto-detection walks up from the current directory and picks the first VCS directory it finds.

Example: If you're in /workspace/git-repo/subdir/ and both /workspace/.hg/ and /workspace/git-repo/.git/ exist, auto-detection will find .git/ first and use the Git provider.

Fix: Override the provider explicitly:

# Force Mercurial for this session
export SASE_VCS_PROVIDER=hg

# Or use config file
# ~/.config/sase/sase.yml
vcs_provider:
  provider: hg

VCS Provider Reference¶

Plugin Architecture¶

Hook Specification¶

Disabling Plugins¶

Provider Selection¶

Tier 1: Environment Variable¶

Tier 2: Configuration File¶

Tier 3: Auto-Detection¶

Per-Command VCS Usage¶

sase commit¶

sase ace TUI Actions¶

Sync (S key)¶

Mail (m key)¶

Show Diff (d key)¶

Revert (X key / status change to "Reverted")¶

Restore (status change from "Reverted" to "WIP"/"Drafted")¶

Archive (status change to "Archived")¶

Reword (w key)¶

sase axe¶

sase revert¶

sase restore¶

Git Provider Details¶

Branch Naming¶

Branch Management¶

PR Integration¶

GitHub Plugin Scope¶

Sync¶

Archive¶

Diff¶

Workspace Info¶

Tag Operations¶

Mercurial Provider Details¶

Core Commands¶

Branch and Workspace Info¶

Description Management¶

Review Operations¶

Diff and Patch¶

Change URL¶

Description Escaping¶

Diff Management¶

Diff Storage Locations¶

Patch Application¶

Stash and Clean¶

Configuration Reference¶

Full sase.yml Example¶

Environment Variable¶

CLI Flags¶

Schema¶

Classification Hooks¶

vcs_detect_repo_type¶

vcs_classify_repo¶

Troubleshooting¶

"No VCS provider found" Error¶

Git: gh CLI Not Installed¶

Mercurial: Plugin Not Installed¶

Mercurial: sase_hg_* Commands Not Found¶

Auto-Detection Picks Wrong Provider in Nested Repos¶

`sase commit`¶

`sase ace` TUI Actions¶

Sync (`S` key)¶

Mail (`m` key)¶

Show Diff (`d` key)¶

Revert (`X` key / status change to "Reverted")¶

Reword (`w` key)¶

`sase axe`¶

`sase revert`¶

`sase restore`¶

Full `sase.yml` Example¶

`vcs_detect_repo_type`¶

`vcs_classify_repo`¶

Git: `gh` CLI Not Installed¶

Mercurial: `sase_hg_*` Commands Not Found¶