Wipe out the database without os.remove

jkseppan · jkseppan · commit e9834574b123 · 2018-01-12T18:07:08.000+02:00
To avoid Windows locking problems
diff --git a/lib/matplotlib/dviread.py b/lib/matplotlib/dviread.py
@@ -1055,17 +1055,26 @@ def __init__(self, filename=None):
             else:
                 _log.warn("%s created with a newer version (%d>%d), deleting",
                           filename, version, self.schema_version)
-                self.connection.close()
-                os.remove(filename)
+                self._wipeout()
 
         while version < self.schema_version:
             version += 1
             self._migrate(version)
 
-    def close(self):
-        """Close the database connection, making the database unusable.
-        Useful mainly in tests."""
-        pass
+    def _wipeout(self):
+        """Wipe out the schema."""
+        with self.connection as conn:
+            conn.executescript(
+                """
+                PRAGMA writable_schema=1;
+                DELETE FROM sqlite_master WHERE type = 'table';
+                DELETE FROM sqlite_master WHERE type = 'view';
+                DELETE FROM sqlite_master WHERE type = 'index';
+                DELETE FROM sqlite_master WHERE type = 'trigger';
+                PRAGMA writable_schema=0;
+                VACUUM;
+                PRAGMA user_version=0;
+                """)
 
     def _migrate(self, version):
         """Update the database schema to the given schema version from
diff --git a/lib/matplotlib/tests/test_dviread.py b/lib/matplotlib/tests/test_dviread.py
@@ -98,13 +98,36 @@ def test_tex_support_cache_versioning(tmpdir):
 
     conn = sqlite3.connect(dbfile, isolation_level="DEFERRED")
     with conn:
-        conn.execute("PRAGMA user_version=1000000000;")
+        conn.executescript(
+            """
+            CREATE TABLE foo (a, b);
+            CREATE TABLE bar (c, d);
+            CREATE INDEX foo_a ON foo (a);
+            CREATE VIEW foo_a0 AS SELECT a FROM foo WHERE a>0;
+            CREATE TRIGGER trig INSERT ON foo WHEN b<0
+            BEGIN INSERT INTO bar VALUES (1,2); END;
+            PRAGMA user_version=1000000000;
+            """)
     conn.close()
 
     # now reopening the cache should wipe it out
     cache2 = dr._tex_support_cache(dbfile)
     assert cache2.get_pathnames(['foo']) == {}
 
+    # there should be no extra objects in the schema
+    conn = sqlite3.connect(dbfile, isolation_level="DEFERRED")
+    with conn:
+        rows = conn.execute(
+            """SELECT name FROM sqlite_master
+            WHERE type IN ('table', 'index', 'trigger', 'view')
+            """).fetchall()
+    assert ('foo',) not in rows
+    assert ('bar',) not in rows
+    assert ('foo_a',) not in rows
+    assert ('foo_a0',) not in rows
+    assert ('trig',) not in rows
+    assert ('file_path',) in rows
+
 
 def test_find_tex_files(tmpdir):
     with mock.patch('matplotlib.dviread.subprocess.Popen') as mock_popen:
