Ticket #8625: sqlite-get_supported_schemes.2

Better reporting of installation issues related to PySqlite.

Use the same mechanism as for errors on VCS connectors (r7435).

Related to #8265.

diff --git a/trac/db/api.py b/trac/db/api.py
--- a/trac/db/api.py
+++ b/trac/db/api.py
@@ -37,6 +37,10 @@
     def get_supported_schemes():
         """Return the connection URL schemes supported by the connector, and
         their relative priorities as an iterable of `(scheme, priority)` tuples.
+        
+        If `priority` is a negative number, this is indicative of an
+        error  condition with the connector. An error message should be 
+        attached to the `error` attribute of the connector.
         """
 
     def get_connection(path, log=None, **kwargs):
@@ -116,18 +120,17 @@
 
     def _get_connector(self): ### FIXME: Make it public?
         scheme, args = _parse_db_str(self.connection_uri)
-        candidates = {}
+        candidates = []
         for connector in self.connectors:
             for scheme_, priority in connector.get_supported_schemes():
                 if scheme_ != scheme:
                     continue
-                highest = candidates.get(scheme_, (None, 0))[1]
-                if priority > highest:
-                    candidates[scheme] = (connector, priority)
-
-        connector = candidates.get(scheme, [None])[0]
-        if not connector:
+                candidates.append((priority, connector))
+        if not candidates:
             raise TracError('Unsupported database type "%s"' % scheme)
+        priority, connector = max(candidates)
+        if priority < 0:
+            raise TracError(connector.error)
 
         if scheme == 'sqlite':
             # Special case for SQLite to support a path relative to the
diff --git a/trac/db/sqlite_backend.py b/trac/db/sqlite_backend.py
--- a/trac/db/sqlite_backend.py
+++ b/trac/db/sqlite_backend.py
@@ -22,6 +22,7 @@
 from trac.db.api import IDatabaseConnector
 from trac.db.util import ConnectionWrapper
 from trac.util import get_pkginfo, getuser
+from trac.util.translation import _
 
 _like_escape_re = re.compile(r'([/_%])')
 
@@ -112,9 +113,18 @@
 
     def __init__(self):
         self._version = None
+        self.error = None
 
     def get_supported_schemes(self):
-        return [('sqlite', 1)]
+        if not have_pysqlite:
+            self.error = _("Coudn't load Python bindings for SQLite")
+        elif sqlite.sqlite_version_info >= (3, 3, 3):
+            if sqlite.version_info < (1, 0, 7):
+                self.error = _("Need at least PySQlite 1.0.7 or higher")
+            elif sqlite.version_info[0] == 2 and \
+                    sqlite.version_info < (2, 0, 7):
+                self.error = _("Need at least PySqlite 2.0.7 or higher")
+        yield ('sqlite', self.error and -1 or 1)
 
     def get_connection(self, path, log=None, params={}):
         if not self._version: