Add implicit Env to Collection if needed

CHANGES.txt

@@ -3,6 +3,15 @@ Changes
 
 All issue numbers are relative to https://github.com/Toblerity/Fiona/issues.
 
+1.8.5 (TBD)
+-----------
+
+- On entering a collection context (Collection.__enter__) a new anonymous GDAL
+  environment is created if needed and entered. This makes `with
+  fiona.open(...) as collection:` roughly equivalent to `with fiona.open(...)
+  as collection, Env():`. This helps prevent bugs when Collections are created
+  and then used later or in different scopes.
+
 1.8.4 (2018-12-10)
 ------------------
 

fiona/collection.py

@@ -11,11 +11,11 @@
 from fiona.ogrext import buffer_to_virtual_file, remove_virtual_file, GEOMETRY_TYPES
 from fiona.errors import (DriverError, SchemaError, CRSError, UnsupportedGeometryTypeError, DriverSupportError)
 from fiona.logutils import FieldSkipLogFilter
-from fiona._env import driver_count, get_gdal_release_name, get_gdal_version_tuple
-from fiona.env import Env
+from fiona._env import get_gdal_release_name, get_gdal_version_tuple
+from fiona.env import env_ctx_if_needed
 from fiona.errors import FionaDeprecationWarning
 from fiona.drvsupport import supported_drivers
-from fiona.path import Path, UnparsedPath, vsi_path, parse_path
+from fiona.path import Path, vsi_path, parse_path
 from six import string_types, binary_type
 
 
@@ -459,10 +459,13 @@ def closed(self):
 
     def __enter__(self):
         logging.getLogger('fiona.ogrext').addFilter(self.field_skip_log_filter)
+        self._env = env_ctx_if_needed()
+        self._env.__enter__()
         return self
 
     def __exit__(self, type, value, traceback):
         logging.getLogger('fiona.ogrext').removeFilter(self.field_skip_log_filter)
+        self._env.__exit__()
         self.close()
 
     def __del__(self):

tests/test_collection.py

@@ -1,14 +1,14 @@
 # Testing collections and workspaces
 
 import datetime
-import logging
 import sys
 import re
 
 import pytest
 
 import fiona
 from fiona.collection import Collection, supported_drivers
+from fiona.env import getenv
 from fiona.errors import FionaValueError, DriverError
 
 from .conftest import WGS84PATTERN
@@ -872,7 +872,7 @@ def test_collection_zip_http():
 
 def test_encoding_option_warning(tmpdir, caplog):
     """There is no ENCODING creation option log warning for GeoJSON"""
-    ds = fiona.Collection(str(tmpdir.join("test.geojson")), "w", driver="GeoJSON", crs="epsg:4326",
+    fiona.Collection(str(tmpdir.join("test.geojson")), "w", driver="GeoJSON", crs="epsg:4326",
             schema={"geometry": "Point", "properties": {"foo": "int"}})
     assert not caplog.text
 
@@ -881,7 +881,21 @@ def test_closed_session_next(path_coutwildrnp_shp):
     """Confirm fix for  issue #687"""
     src = fiona.open(path_coutwildrnp_shp)
     itr = iter(src)
-    feats = list(itr)
+    list(itr)
     src.close()
     with pytest.raises(FionaValueError):
         next(itr)
+
+
+def test_collection_no_env(path_coutwildrnp_shp):
+    """We have no GDAL env left over from open"""
+    collection = fiona.open(path_coutwildrnp_shp)
+    assert collection
+    with pytest.raises(Exception):
+        getenv()
+
+
+def test_collection_env(path_coutwildrnp_shp):
+    """We have a GDAL env within collection context"""
+    with fiona.open(path_coutwildrnp_shp):
+        assert 'FIONA_ENV' in getenv()