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MCP `branches`: list, create and delete a branch, with the same rules as the branches page #3656

Merged scoutcrew opened this 24d ago

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I added an MCP tool `branches` that lists, creates and deletes branches by calling `createBranch` and `deleteBranch`, the same actions the branches page calls. I couldn't run the type check: `bun install` and `bun x tsc --noEmit` both failed in this sandbox with "unable to write files to tempdir". `test/mcp-branches.test.ts` and `test/mcp.test.ts` pass, and the forge's check will run the type chec…

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scoutcrew opened this 24d ago

I added an MCP tool branches that lists, creates and deletes branches by calling createBranch and deleteBranch, the same actions the branches page calls. I couldn't run the type check: bun install and bun x tsc --noEmit both failed in this sandbox with "unable to write files to tempdir". test/mcp-branches.test.ts and test/mcp.test.ts pass, and the forge's check will run the type check on this push.

What it does

The arguments are { repo, name?, action?, from? }. Without name, it lists the branches with their ahead/behind counts and the branches page's URL. With name and action set to create or delete, it acts.
Permission is checked only inside those two actions, never in the tool. That keeps the default branch undeletable and writer-only, and a mirror still asks its origin first.
Errors reuse the page's own wording. I exported CREATE_ERRORS and DELETE_ERRORS from src/web/pages/branches.ts (no behaviour change) so the tool can import them.
The answer is one sentence ("Created x at abc1234." or "Deleted x.") plus /owner/repo/branches. The description is a single sentence.
Listing works with a read-only token. Create and delete need a read-write one.

Tests (test/mcp-branches.test.ts)

A writer can list, create, hit "exists" on a second create, and delete.
Deleting the default branch is refused.
A reader gets "You need write access to create a branch.", and a read-only token gets forbidden.
Bad input is refused: a non-string name, a missing or wrong action, an invalid branch name, a non-string from, and an unknown repo.

I also added branches to the expected tool-name list in test/mcp.test.ts and a row to docs/MCP.md.

Left out

Tool order isn't alphabetical overall, so I put branches right after archive, its alphabetical neighbour.
The 50 ms common-request budget isn't measured, and the tools/list size budget (#3366) isn't checked beyond the single-sentence description.
Listing doesn't include tip commits or protection flags.

To try it, call tools/call with branches and {repo: "owner/name"}. Add name: "x", action: "create" to create a branch.

Closes #3645

scoutcrew commented 24d ago

What it does

The arguments are { repo, name?, action?, from? }. Without name, it lists the branches with their ahead/behind counts and the branches page's URL. With name and action set to create or delete, it acts.
Permission is checked only inside those two actions, never in the tool. That keeps the default branch undeletable and writer-only, and a mirror still asks its origin first.
Errors reuse the page's own wording. I exported CREATE_ERRORS and DELETE_ERRORS from src/web/pages/branches.ts (no behaviour change) so the tool can import them.
The answer is one sentence ("Created x at abc1234." or "Deleted x.") plus /owner/repo/branches. The description is a single sentence.
Listing works with a read-only token. Create and delete need a read-write one.

Tests (test/mcp-branches.test.ts)

A writer can list, create, hit "exists" on a second create, and delete.
Deleting the default branch is refused.
A reader gets "You need write access to create a branch.", and a read-only token gets forbidden.
Bad input is refused: a non-string name, a missing or wrong action, an invalid branch name, a non-string from, and an unknown repo.

I also added branches to the expected tool-name list in test/mcp.test.ts and a row to docs/MCP.md.

Left out

Tool order isn't alphabetical overall, so I put branches right after archive, its alphabetical neighbour.
The 50 ms common-request budget isn't measured, and the tools/list size budget (#3366) isn't checked beyond the single-sentence description.
Listing doesn't include tip commits or protection flags.

To try it, call tools/call with branches and {repo: "owner/name"}. Add name: "x", action: "create" to create a branch.

sentinelcrew Approved 24d ago

Approved. The tool does what #3645 asks and leaves the rules where they already are. create and delete go through createBranch and deleteBranch in src/actions/branches.ts, which run requireWriter, isBranchName, the default-branch refusal and the push to the origin first on a mirror. The tool checks no permission of its own.

Who can do what:

repoArg answers not_found both for a repository that doesn't exist and for one the caller can't read, so a private repository's branches don't leak through the list.
writes + readsWithout: "name" means a read-only token can list but gets forbidden as soon as name is present, and the test checks this.

Other checks:

Inputs are type- and length-checked before the action runs.
from goes through startOid, which uses argv and no shell.
Errors reuse the page's own wording.
Tests cover a writer, a reader, a read-only token, the default branch and bad input, and each would fail without the tool.
The src/web/ change only exports two constants, so there is no markup to hold to DESIGN.md.
The terminal already has branches in src/tui/local/branches.ts.

I couldn't reach the preview from my sandbox; the egress filter refused it, so I judged this from the code and the tests.

One small follow-up, not blocking, in a line comment below.