Add auto-vendor support to git go-patch

[gdams]

Summary

Add a new git go-patch command that eliminates the need to store vendor directory contents in patch files. This reduces the microsoft-go vendor patch (0001) from ~43,000 lines to ~240 lines.

How it works

A patch commit message can include the command:

github.com/microsoft/go-infra/cmd/git-go-patch command: auto vendor src src/cmd

During extract

Diff hunks for vendor directories (src/vendor/, src/cmd/vendor/) are automatically stripped from the patch file. Only go.mod, go.sum, and other non-vendor files are preserved.

During apply

Patches with auto-vendor commands are applied individually. After each such patch, go mod vendor is run in the specified module directories and the commit is amended to include the regenerated vendor tree.

Example: new patch 0001

The current 0001-Vendor-external-dependencies.patch in microsoft-go is ~43,000 lines of vendored Go source. With auto-vendor, it becomes ~240 lines:

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: bot-for-go[bot] <...>
Subject: [PATCH] Vendor external dependencies

Vendor directories are automatically regenerated by 'git go-patch apply'
using 'go mod vendor' in 'src' and 'src/cmd'. This patch only tracks
go.mod, go.sum, and related non-vendor files in source control.

github.com/microsoft/go-infra/cmd/git-go-patch command: auto vendor src src/cmd
---
diff --git a/src/cmd/go.mod b/src/cmd/go.mod
  (go.mod changes)
diff --git a/src/cmd/go.sum b/src/cmd/go.sum
  (go.sum changes)
diff --git a/src/go.mod b/src/go.mod
  (go.mod changes)
diff --git a/src/go.sum b/src/go.sum
  (go.sum changes)
  ... plus a few small non-vendor files (~240 lines total)

Changes

New files

• patch/commands.go — Shared command parsing (constants + ReadPatchCommands, ScanAutoVendorPatches)
• patch/vendor.go — FilterVendorContent (strips vendor diffs), VendorPathsFromModDirs, RunGoModVendor
• patch/vendor_test.go — Tests for filtering and vendor path logic

Modified files

• patch/patch.go — Added ApplyIndividually (per-patch apply with callback)
• cmd/git-go-patch/extract.go — Uses shared constants/functions from patch package; filters vendor content during extract
• cmd/git-go-patch/apply.go — Pre-scans for auto-vendor patches; uses ApplyIndividually + RunGoModVendor
• cmd/git-go-patch/git-go-patch.go — Version bump to v1.1.0

Companion change

The microsoft-go repo will need a follow-up PR to:

• Bump .git-go-patch MinimumToolVersion to v1.1.0
• Replace the current ~43k-line 0001-Vendor-external-dependencies.patch with the ~240-line version
• Update eng/_util/cmd/submodule-refresh/submodule-refresh.go to use ScanAutoVendorPatches + ApplyIndividually

[Copilot]

Pull request overview

This PR adds an “auto-vendor” workflow to git go-patch so vendor directory contents don’t need to be stored in patch files. It does this by stripping vendor diffs during extract, and regenerating/staging vendor trees via go mod vendor during apply, dramatically reducing patch size for vendored changes.

Changes:

• Introduces shared patch-command parsing and auto-vendor patch scanning in the patch package.
• Adds vendor-diff filtering during extract and per-patch apply support (with post-apply callbacks) to enable go mod vendor between patches.
• Updates apply to detect auto-vendor patches and amend commits with regenerated vendor trees; bumps tool version to v1.1.0.

Show a summary per file

File	Description
patch/vendor.go	Adds vendor-diff filtering plus go mod vendor execution/staging/amend support.
patch/vendor_test.go	Adds unit tests for vendor filtering and vendor-path detection logic.
patch/patch.go	Adds ApplyIndividually to apply patches one-by-one with an after-apply hook.
patch/commands.go	Adds shared command constants, patch command parsing, and auto-vendor patch scanning.
cmd/git-go-patch/extract.go	Uses shared command parsing; strips vendor diffs when auto-vendor is specified.
cmd/git-go-patch/apply.go	Pre-scans for auto-vendor patches and applies patches individually with vendor regeneration.
cmd/git-go-patch/git-go-patch.go	Bumps tool version to v1.1.0.

Copilot's findings

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• Files reviewed: 7/7 changed files
• Comments generated: 4

[dagood]

After each such patch, go mod vendor is run in the specified module directories

The go used to run go mod vendor has to match the source tree exactly (not just >), how is that handled?

Overall, I don't think this approach makes sense (at least I can't justify it in my head as a reviewer vs. what seems possible), it seems super complicated and has many performance implications.

(I know this is a draft, but it already has a release on merge label...)