gc: Introduce new command to remove old projects

When projects are removed from manifest, they are only removed from
worktree and not from .repo/projects and .repo/project-objects. Keeping
data under .repo can be desired if user expects deleted projects to be
restored (e.g. checking out a release branch).

Android has ongoing effort to remove many stale projects and this change
allows users to easily free-up their disk space.

Bug: b/344018971
Bug: 40013312
Change-Id: Id23c7524a88082ee6db908f9fd69dcd5d0c4f681
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/445921


Reviewed-by: Mike Frysinger <vapier@google.com>
Commit-Queue: Josip Sokcevic <sokcevic@chromium.org>
Reviewed-by: Gavin Mak <gavinmak@google.com>
Tested-by: Josip Sokcevic <sokcevic@chromium.org>

man/repo-gc.1

+.\" DO NOT MODIFY THIS FILE!  It was generated by help2man.
+.TH REPO "1" "December 2024" "repo gc" "Repo Manual"
+.SH NAME
+repo \- repo gc - manual page for repo gc
+.SH SYNOPSIS
+.B repo
+\fI\,gc\/\fR
+.SH DESCRIPTION
+Summary
+.PP
+Cleaning up internal repo state.
+.SH OPTIONS
+.TP
+\fB\-h\fR, \fB\-\-help\fR
+show this help message and exit
+.TP
+\fB\-n\fR, \fB\-\-dry\-run\fR
+do everything except actually delete
+.TP
+\fB\-y\fR, \fB\-\-yes\fR
+answer yes to all safe prompts
+.SS Logging options:
+.TP
+\fB\-v\fR, \fB\-\-verbose\fR
+show all output
+.TP
+\fB\-q\fR, \fB\-\-quiet\fR
+only show errors
+.SS Multi\-manifest options:
+.TP
+\fB\-\-outer\-manifest\fR
+operate starting at the outermost manifest
+.TP
+\fB\-\-no\-outer\-manifest\fR
+do not operate on outer manifests
+.TP
+\fB\-\-this\-manifest\-only\fR
+only operate on this (sub)manifest
+.TP
+\fB\-\-no\-this\-manifest\-only\fR, \fB\-\-all\-manifests\fR
+operate on this manifest and its submanifests
+.PP
+Run `repo help gc` to view the detailed manual.

man/repo-manifest.1

 .\" DO NOT MODIFY THIS FILE!  It was generated by help2man.
-.TH REPO "1" "April 2024" "repo manifest" "Repo Manual"
+.TH REPO "1" "December 2024" "repo manifest" "Repo Manual"
 .SH NAME
 repo \- repo manifest - manual page for repo manifest
 .SH SYNOPSIS
@@ -192,11 +192,13 @@ CDATA #IMPLIED>
 <!ATTLIST extend\-project remote CDATA #IMPLIED>
 <!ATTLIST extend\-project dest\-branch CDATA #IMPLIED>
 <!ATTLIST extend\-project upstream CDATA #IMPLIED>
+<!ATTLIST extend\-project base\-rev CDATA #IMPLIED>
 .IP
 <!ELEMENT remove\-project EMPTY>
 <!ATTLIST remove\-project name     CDATA #IMPLIED>
 <!ATTLIST remove\-project path     CDATA #IMPLIED>
 <!ATTLIST remove\-project optional CDATA #IMPLIED>
+<!ATTLIST remove\-project base\-rev CDATA #IMPLIED>
 .IP
 <!ELEMENT repo\-hooks EMPTY>
 <!ATTLIST repo\-hooks in\-project CDATA #REQUIRED>
@@ -495,6 +497,14 @@ project. Same syntax as the corresponding element of `project`.
 Attribute `upstream`: If specified, overrides the upstream of the original
 project. Same syntax as the corresponding element of `project`.
 .PP
+Attribute `base\-rev`: If specified, adds a check against the revision to be
+extended. Manifest parse will fail and give a list of mismatch extends if the
+revisions being extended have changed since base\-rev was set. Intended for use
+with layered manifests using hash revisions to prevent patch branches hiding
+newer upstream revisions. Also compares named refs like branches or tags but is
+misleading if branches are used as base\-rev. Same syntax as the corresponding
+element of `project`.
+.PP
 Element annotation
 .PP
 Zero or more annotation elements may be specified as children of a project or
@@ -556,6 +566,14 @@ Logic otherwise behaves like both are specified.
 Attribute `optional`: Set to true to ignore remove\-project elements with no
 matching `project` element.
 .PP
+Attribute `base\-rev`: If specified, adds a check against the revision to be
+removed. Manifest parse will fail and give a list of mismatch removes if the
+revisions being removed have changed since base\-rev was set. Intended for use
+with layered manifests using hash revisions to prevent patch branches hiding
+newer upstream revisions. Also compares named refs like branches or tags but is
+misleading if branches are used as base\-rev. Same syntax as the corresponding
+element of `project`.
+.PP
 Element repo\-hooks
 .PP
 NB: See the [practical documentation](./repo\-hooks.md) for using repo hooks.

man/repo.1

 .\" DO NOT MODIFY THIS FILE!  It was generated by help2man.
-.TH REPO "1" "April 2024" "repo" "Repo Manual"
+.TH REPO "1" "December 2024" "repo" "Repo Manual"
 .SH NAME
 repo \- repository management tool built on top of git
 .SH SYNOPSIS
@@ -79,6 +79,9 @@ Download and checkout a change
 forall
 Run a shell command in each project
 .TP
+gc
+Cleaning up internal repo state.
+.TP
 grep
 Print lines matching a pattern
 .TP

subcmds/gc.py

+# Copyright (C) 2024 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import os
+from typing import Set
+
+from command import Command
+import platform_utils
+from progress import Progress
+
+
+class Gc(Command):
+    COMMON = True
+    helpSummary = "Cleaning up internal repo state."
+    helpUsage = """
+%prog
+"""
+
+    def _Options(self, p):
+        p.add_option(
+            "-n",
+            "--dry-run",
+            dest="dryrun",
+            default=False,
+            action="store_true",
+            help="do everything except actually delete",
+        )
+        p.add_option(
+            "-y",
+            "--yes",
+            default=False,
+            action="store_true",
+            help="answer yes to all safe prompts",
+        )
+
+    def _find_git_to_delete(
+        self, to_keep: Set[str], start_dir: str
+    ) -> Set[str]:
+        """Searches no longer needed ".git" directories.
+
+        Scans the file system starting from `start_dir` and removes all
+        directories that end with ".git" that are not in the `to_keep` set.
+        """
+        to_delete = set()
+        for root, dirs, _ in platform_utils.walk(start_dir):
+            for directory in dirs:
+                if not directory.endswith(".git"):
+                    continue
+
+                path = os.path.join(root, directory)
+                if path not in to_keep:
+                    to_delete.add(path)
+
+        return to_delete
+
+    def Execute(self, opt, args):
+        projects = self.GetProjects(
+            args, all_manifests=not opt.this_manifest_only
+        )
+        print(f"Scanning filesystem under {self.repodir}...")
+
+        project_paths = set()
+        project_object_paths = set()
+
+        for project in projects:
+            project_paths.add(project.gitdir)
+            project_object_paths.add(project.objdir)
+
+        to_delete = self._find_git_to_delete(
+            project_paths, os.path.join(self.repodir, "projects")
+        )
+
+        to_delete.update(
+            self._find_git_to_delete(
+                project_object_paths,
+                os.path.join(self.repodir, "project-objects"),
+            )
+        )
+
+        if not to_delete:
+            print("Nothing to clean up.")
+            return
+
+        print("Identified the following projects are no longer used:")
+        print("\n".join(to_delete))
+        print("\n")
+        if not opt.yes:
+            print(
+                "If you proceed, any local commits in those projects will be "
+                "destroyed!"
+            )
+            ask = input("Proceed? [y/N] ")
+            if ask.lower() != "y":
+                return 1
+
+        pm = Progress(
+            "Deleting",
+            len(to_delete),
+            delay=False,
+            quiet=opt.quiet,
+            show_elapsed=True,
+            elide=True,
+        )
+
+        for path in to_delete:
+            if opt.dryrun:
+                print(f"\nWould have deleted ${path}")
+            else:
+                tmp_path = os.path.join(
+                    os.path.dirname(path),
+                    f"to_be_deleted_{os.path.basename(path)}",
+                )
+                platform_utils.rename(path, tmp_path)
+                platform_utils.rmtree(tmp_path)
+            pm.update(msg=path)
+        pm.end()