Don't print a traceback if we pass a single, missing argument to diffoscope...

Don't print a traceback if we pass a single, missing argument to diffoscope (eg. a JSON diff to re-load).

diffoscope/comparators/utils/compare.py

@@ -19,7 +19,6 @@
 
 import io
 import os
-import sys
 import shlex
 import logging
 import binascii
@@ -27,6 +26,7 @@ import subprocess
 
 from diffoscope.tools import tool_required
 from diffoscope.exc import RequiredToolNotFound
+from diffoscope.utils import bail_if_non_existing
 from diffoscope.config import Config
 from diffoscope.excludes import any_excluded
 from diffoscope.profiling import profile
@@ -147,16 +147,6 @@ def call_difftool(file1, file2):
     subprocess.call(cmd, shell=True)
 
 
-def bail_if_non_existing(*paths):
-    if not all(map(os.path.lexists, paths)):
-        for path in paths:
-            if not os.path.lexists(path):
-                sys.stderr.write(
-                    '%s: %s: No such file or directory\n' % (sys.argv[0], path)
-                )
-        sys.exit(2)
-
-
 def compare_binary_files(file1, file2, source=None):
     try:
         if source is None:

diffoscope/readers/__init__.py

@@ -3,7 +3,7 @@
 # diffoscope: in-depth comparison of files, archives, and directories
 #
 # Copyright © 2017 Ximin Luo <infinity0@debian.org>
-# Copyright © 2017 Chris Lamb <lamby@debian.org>
+# Copyright © 2017, 2020 Chris Lamb <lamby@debian.org>
 #
 # diffoscope is free software: you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by
@@ -20,10 +20,13 @@
 
 import codecs
 
+from diffoscope.utils import bail_if_non_existing
+
 from .json import JSONReaderV1
 
 
 def load_diff_from_path(path):
+    bail_if_non_existing(path)
     with open(path, 'rb') as fp:
         return load_diff(codecs.getreader('utf-8')(fp), path)
 

diffoscope/utils.py

@@ -17,6 +17,9 @@
 # You should have received a copy of the GNU General Public License
 # along with diffoscope.  If not, see <https://www.gnu.org/licenses/>.
 
+import os
+import sys
+
 
 def format_cmdline(cmd, replace=(), truncate=None):
     def fn(x):
@@ -44,3 +47,13 @@ def format_bytes(size, decimal_places=2):
         size /= 1024.0
 
     return f"{size:.{decimal_places}f} {unit}"
+
+
+def bail_if_non_existing(*paths):
+    if not all(map(os.path.lexists, paths)):
+        for path in paths:
+            if not os.path.lexists(path):
+                sys.stderr.write(
+                    '%s: %s: No such file or directory\n' % (sys.argv[0], path)
+                )
+        sys.exit(2)