D6722: fncache: make debugrebuildfncache not fail on broken fncache

valentin.gatienbaron (Valentin Gatien-Baron) phabricator at mercurial-scm.org
Mon Aug 12 14:13:33 EDT 2019

valentin.gatienbaron created this revision.
Herald added subscribers: mercurial-devel, mjpieters.
Herald added a reviewer: hg-reviewers.

  The code reading the fncache changed in 5.0, to complain if the file
  is not \n terminated. This makes apparent the fact that the fncache
  gets corrupted.
  Make it possible to recover, instead of having `hg
  debugrebuildfncache` failing by saying `(run hg debugrebuildfncache)`.
  The corruption itself is most likely due to hg not using fsync in
  general, and so various bad things can happen. Here, the reported
  problems happened when running out of disk space. So I suspect that
  because the fncache is much bigger than the average commit/pull, when
  running out of disk space, the bulk of the pull may succeed, but the
  new fncache may get half-written and still renamed into place.

  rHG Mercurial




diff --git a/tests/test-fncache.t b/tests/test-fncache.t
--- a/tests/test-fncache.t
+++ b/tests/test-fncache.t
@@ -435,16 +435,18 @@
-debugrebuildfncache fails to recover from truncated line in fncache
+debugrebuildfncache recovers from truncated line in fncache
   $ printf a > .hg/store/fncache
   $ hg debugrebuildfncache
-  abort: fncache does not ends with a newline
-  (use 'hg debugrebuildfncache' to rebuild the fncache)
-  [255]
+  fncache does not ends with a newline
+  adding data/.bar.i
+  adding data/foo.i
+  2 items added, 0 removed from fncache
   $ cat .hg/store/fncache | sort
-  a
+  data/.bar.i
+  data/foo.i
   $ cd ..
diff --git a/mercurial/store.py b/mercurial/store.py
--- a/mercurial/store.py
+++ b/mercurial/store.py
@@ -458,7 +458,15 @@
         # set of new additions to fncache
         self.addls = set()
-    def _load(self):
+    def ensureloaded(self, warn=None):
+        '''read the fncache file if not already read.
+        If the file on disk is corrupted, raise. If warn is provided,
+        warn and keep going instead.'''
+        if self.entries is None:
+            self._load(warn)
+    def _load(self, warn=None):
         '''fill the entries from the fncache file'''
         self._dirty = False
@@ -482,20 +490,27 @@
         if chunk:
-            raise error.Abort(_("fncache does not ends with a newline"),
-                              hint=_("use 'hg debugrebuildfncache' to rebuild"
-                                     " the fncache"))
-        self._checkentries(fp)
+            msg = _("fncache does not ends with a newline")
+            if warn:
+                warn(msg + '\n')
+            else:
+                raise error.Abort(msg,
+                                  hint=_("use 'hg debugrebuildfncache' to "
+                                         "rebuild the fncache"))
+        self._checkentries(fp, warn)
-    def _checkentries(self, fp):
+    def _checkentries(self, fp, warn):
         """ make sure there is no empty string in entries """
         if '' in self.entries:
             for n, line in enumerate(util.iterfile(fp)):
                 if not line.rstrip('\n'):
                     t = _('invalid entry in fncache, line %d') % (n + 1)
-                    raise error.Abort(t)
+                    if warn:
+                        warn(t + '\n')
+                    else:
+                        raise error.Abort(t)
     def write(self, tr):
         if self._dirty:
diff --git a/mercurial/repair.py b/mercurial/repair.py
--- a/mercurial/repair.py
+++ b/mercurial/repair.py
@@ -392,9 +392,7 @@
     with repo.lock():
         fnc = repo.store.fncache
-        # Trigger load of fncache.
-        if 'irrelevant' in fnc:
-            pass
+        fnc.ensureloaded(warn=ui.warn)
         oldentries = set(fnc.entries)
         newentries = set()

To: valentin.gatienbaron, #hg-reviewers
Cc: mjpieters, mercurial-devel

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