Add envar to replace shallow clones with partial

An investigation go/git-repo-shallow shows a number of problems
when doing a shallow git fetch/clone. This change introduces an
environment variable REPO_ALLOW_SHALLOW. When this environment variable
is set to 1 during a repo init or repo sync all shallow git fetch
commands are replaced with partial fetch commands. Any shallow
repository needing update is unshallowed. This behavior continues until
a subsequent repo sync command is run with REPO_ALLOW_SHALLOW set to 1.

Bug: b/274340522
Change-Id: I1c3188270629359e52449788897d9d4988ebf280
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/374754
Reviewed-by: Josip Sokcevic <sokcevic@google.com>
Tested-by: Jason Chang <jasonnc@google.com>

project.py

@@ -1186,6 +1186,7 @@ class Project(object):
         ssh_proxy=None,
         clone_filter=None,
         partial_clone_exclude=set(),
+        clone_filter_for_depth=None,
     ):
         """Perform only the network IO portion of the sync process.
         Local working directory/branch state is not affected.
@@ -1295,6 +1296,10 @@ class Project(object):
         else:
             depth = self.manifest.manifestProject.depth
 
+        if depth and clone_filter_for_depth:
+            depth = None
+            clone_filter = clone_filter_for_depth
+
         # See if we can skip the network fetch entirely.
         remote_fetched = False
         if not (
@@ -3884,6 +3889,11 @@ class ManifestProject(MetaProject):
         """Partial clone exclude string"""
         return self.config.GetString("repo.partialcloneexclude")
 
+    @property
+    def clone_filter_for_depth(self):
+        """Replace shallow clone with partial clone."""
+        return self.config.GetString("repo.clonefilterfordepth")
+
     @property
     def manifest_platform(self):
         """The --platform argument from `repo init`."""
@@ -3961,6 +3971,7 @@ class ManifestProject(MetaProject):
             manifest_name=spec.manifestName,
             this_manifest_only=True,
             outer_manifest=False,
+            clone_filter_for_depth=mp.clone_filter_for_depth,
         )
 
     def Sync(
@@ -3991,6 +4002,7 @@ class ManifestProject(MetaProject):
         tags="",
         this_manifest_only=False,
         outer_manifest=True,
+        clone_filter_for_depth=None,
     ):
         """Sync the manifest and all submanifests.
 
@@ -4035,6 +4047,8 @@ class ManifestProject(MetaProject):
                 current sub manifest.
             outer_manifest: a boolean, whether to start at the outermost
                 manifest.
+            clone_filter_for_depth: a string, when specified replaces shallow
+                clones with partial.
 
         Returns:
             a boolean, whether the sync was successful.
@@ -4297,6 +4311,9 @@ class ManifestProject(MetaProject):
                     file=sys.stderr,
                 )
 
+        if clone_filter_for_depth is not None:
+            self.ConfigureCloneFilterForDepth(clone_filter_for_depth)
+
         if use_superproject is not None:
             self.config.SetBoolean("repo.superproject", use_superproject)
 
@@ -4311,6 +4328,7 @@ class ManifestProject(MetaProject):
                 submodules=submodules,
                 clone_filter=clone_filter,
                 partial_clone_exclude=self.manifest.PartialCloneExclude,
+                clone_filter_for_depth=self.manifest.CloneFilterForDepth,
             ).success
             if not success:
                 r = self.GetRemote()
@@ -4415,6 +4433,18 @@ class ManifestProject(MetaProject):
 
         return True
 
+    def ConfigureCloneFilterForDepth(self, clone_filter_for_depth):
+        """Configure clone filter to replace shallow clones.
+
+        Args:
+            clone_filter_for_depth: a string or None, e.g. 'blob:none' will
+            disable shallow clones and replace with partial clone. None will
+            enable shallow clones.
+        """
+        self.config.SetString(
+            "repo.clonefilterfordepth", clone_filter_for_depth
+        )
+
     def _ConfigureDepth(self, depth):
         """Configure the depth we'll sync down.