Fixup log_file commit

pre_commit/clientlib.py

@@ -53,7 +53,7 @@ MANIFEST_HOOK_DICT = schema.Map(
         '^$',
     ),
     schema.Optional('language_version', schema.check_string, 'default'),
-    schema.OptionalNoDefault('log_file', schema.check_string),
+    schema.Optional('log_file', schema.check_string, ''),
     schema.Optional('minimum_pre_commit_version', schema.check_string, '0'),
     schema.Optional('stages', schema.check_array(schema.check_string), []),
 )

pre_commit/commands/run.py

@@ -121,10 +121,7 @@ def _run_single_hook(hook, repo, args, skips, cols):
         for out in (stdout, stderr):
             assert type(out) is bytes, type(out)
             if out.strip():
-                output.write_line(
-                    out.strip(),
-                    logfile_name=hook.get('log_file'),
-                )
+                output.write_line(out.strip(), logfile_name=hook['log_file'])
         output.write_line()
 
     return retcode

pre_commit/output.py

@@ -4,6 +4,7 @@ import sys
 
 from pre_commit import color
 from pre_commit import five
+from pre_commit.util import noop_context
 
 
 def get_hook_message(
@@ -72,16 +73,16 @@ def write(s, stream=stdout_byte_stream):
 
 
 def write_line(s=None, stream=stdout_byte_stream, logfile_name=None):
-    def output_streams():
-        yield stream
-        try:
-            with open(logfile_name, 'ab') as logfile:
-                yield logfile
-        except (TypeError, IOError):
-            pass
+    output_streams = [stream]
+    if logfile_name:
+        ctx = open(logfile_name, 'ab')
+        output_streams.append(ctx)
+    else:
+        ctx = noop_context()
 
-    for output_stream in output_streams():
-        if s is not None:
-            output_stream.write(five.to_bytes(s))
-        output_stream.write(b'\n')
-        output_stream.flush()
+    with ctx:
+        for output_stream in output_streams:
+            if s is not None:
+                output_stream.write(five.to_bytes(s))
+            output_stream.write(b'\n')
+            output_stream.flush()