sharesafe: add functionality to automatically downgrade shares

Reasoning is same as previous patch which adds automatic upgrade support.

Downgrade is required as if automatic upgrade is enabled, all shares upgrade and
then source repository downgrades, shares won't work. We need to downgrade them.

Differential Revision: https://phab.mercurial-scm.org/D9680

mercurial/configitems.py

@@ -1074,6 +1074,11 b' coreconfigitem('
 )
 coreconfigitem(
     b'experimental',
+    b'sharesafe-auto-downgrade-shares',
+    default=False,
+)
+coreconfigitem(
+    b'experimental',
     b'sharesafe-auto-upgrade-shares',
     default=False,
 )

mercurial/localrepo.py

@@ -574,11 +574,26 b' def makelocalrepository(baseui, path, in'
             and requirementsmod.SHARESAFE_REQUIREMENT
             not in _readrequires(sharedvfs, True)
         ):
-            raise error.Abort(
-                _(b"share source does not support exp-sharesafe requirement")
-            )
-
-        requirements |= _readrequires(storevfs, False)
+            if ui.configbool(
+                b'experimental', b'sharesafe-auto-downgrade-shares'
+            ):
+                # prevent cyclic import localrepo -> upgrade -> localrepo
+                from . import upgrade
+
+                upgrade.downgrade_share_to_non_safe(
+                    ui,
+                    hgvfs,
+                    sharedvfs,
+                    requirements,
+                )
+            else:
+                raise error.Abort(
+                    _(
+                        b"share source does not support exp-sharesafe requirement"
+                    )
+                )
+        else:
+            requirements |= _readrequires(storevfs, False)
     elif shared:
         sourcerequires = _readrequires(sharedvfs, False)
         if requirementsmod.SHARESAFE_REQUIREMENT in sourcerequires:

mercurial/upgrade.py

@@ -264,3 +264,34 b' def upgrade_share_to_safe(ui, hgvfs, sto'
     finally:
         if wlock:
             wlock.release()
+
+
+def downgrade_share_to_non_safe(
+    ui,
+    hgvfs,
+    sharedvfs,
+    current_requirements,
+):
+    """Downgrades a share which use share-safe to not use it"""
+    wlock = None
+    try:
+        wlock = lockmod.trylock(ui, hgvfs, b'wlock', 0, 0)
+        source_requirements = localrepo._readrequires(sharedvfs, True)
+        # we cannot be 100% sure on which requirements were present in store when
+        # the source supported share-safe. However, we do know that working
+        # directory requirements were not there. Hence we remove them
+        source_requirements -= requirementsmod.WORKING_DIR_REQUIREMENTS
+        current_requirements |= source_requirements
+        current_requirements.remove(requirementsmod.SHARESAFE_REQUIREMENT)
+        scmutil.writerequires(hgvfs, current_requirements)
+        ui.warn(_(b'repository downgraded to not use share-safe mode\n'))
+    except error.LockError as e:
+        # raise error right away because if downgrade failed, we cannot load
+        # the repository because it does not have complete set of requirements
+        raise error.Abort(
+            _(b'failed to downgrade share, got error: %s')
+            % stringutil.forcebytestr(e.strerror)
+        )
+    finally:
+        if wlock:
+            wlock.release()

tests/test-share-safe.t

@@ -484,6 +484,27 b' Make sure existing shares still works'
   abort: share source does not support exp-sharesafe requirement
   [255]
 
+Testing automatic downgrade of shares when config is set
+
+  $ touch ../ss-share/.hg/wlock
+  $ hg log -GT "{node}: {desc}\n" -R ../ss-share --config experimental.sharesafe-auto-downgrade-shares=true
+  abort: failed to downgrade share, got error: Lock held
+  [255]
+  $ rm ../ss-share/.hg/wlock
+
+  $ hg log -GT "{node}: {desc}\n" -R ../ss-share --config experimental.sharesafe-auto-downgrade-shares=true
+  repository downgraded to not use share-safe mode
+  @  f63db81e6dde1d9c78814167f77fb1fb49283f4f: added bar
+  |
+  o  f3ba8b99bb6f897c87bbc1c07b75c6ddf43a4f77: added foo
+  
+
+  $ hg log -GT "{node}: {desc}\n" -R ../ss-share
+  @  f63db81e6dde1d9c78814167f77fb1fb49283f4f: added bar
+  |
+  o  f3ba8b99bb6f897c87bbc1c07b75c6ddf43a4f77: added foo
+  
+
 
 Testing automatic upgrade of shares when config is set