[gobject-introspection] cachestore: handle cache getting deleted while loading it. Fixes #278

[Christoph Reiter <creiter src gnome org>]

commit 2e9554ec13e362dc1d289e2f4ba4ad79e1c1ef1a
Author: Christoph Reiter <reiter christoph gmail com>
Date:   Wed Apr 17 20:33:12 2019 +0200

    cachestore: handle cache getting deleted while loading it. Fixes #278
    
    In the unlucky event where the cache gets deleted after the os.path.exists()
    check but before we get its mtime things would error out.
    
    Instead of using os.path.exists() handle the exceptions of the operations
    which we expect to possibly fail.

 giscanner/cachestore.py | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)
---
diff --git a/giscanner/cachestore.py b/giscanner/cachestore.py
index e98b52f1..baaaf1ed 100644
--- a/giscanner/cachestore.py
+++ b/giscanner/cachestore.py
@@ -106,8 +106,12 @@ class CacheStore(object):
         return os.path.join(self._directory, hexdigest)
 
     def _cache_is_valid(self, store_filename, filename):
-        return (os.stat(store_filename).st_mtime >=
-                os.stat(filename).st_mtime)
+        try:
+            store_mtime = os.stat(store_filename).st_mtime
+        except FileNotFoundError:
+            return False
+
+        return store_mtime >= os.stat(filename).st_mtime
 
     def _remove_filename(self, filename):
         try:
@@ -130,7 +134,7 @@ class CacheStore(object):
         if store_filename is None:
             return
 
-        if (os.path.exists(store_filename) and self._cache_is_valid(store_filename, filename)):
+        if self._cache_is_valid(store_filename, filename):
             return None
 
         tmp_fd, tmp_filename = tempfile.mkstemp(prefix='g-ir-scanner-cache-')