add support for os.path.exists when new --git flag is used

We need to be able to accept args such as /dev/null and /dev/stdin and these do not meet truth test with os.path.isfile.  See source-foundry#48 (comment) for discussion

Author: chrissimpkins

lib/fdiff/__main__.py

@@ -8,7 +8,7 @@
 from fdiff.color import color_unified_diff_line
 from fdiff.diff import external_diff, u_diff
 from fdiff.textiter import head, tail
-from fdiff.utils import file_exists, get_tables_argument_list
+from fdiff.utils import path_exists, get_tables_argument_list
 
 
 def main():  # pragma: no cover
@@ -86,9 +86,16 @@ def run(argv):
     args, positionals = parser.parse_known_args(argv)
 
     inputs = argparse.Namespace()
+    include_dir_paths = False
     if args.git:
         inputs.PREFILE = args.git[1]
         inputs.POSTFILE = args.git[4]
+        # If the --git flag is used, we need to accept arguments
+        # that do not meet the definition of a file path using
+        # os.path.exists instead of os.path.isfile
+        # See https://github.com/source-foundry/fdiff/pull/48#discussion_r410424497
+        # for additional details
+        include_dir_paths = True
     else:
         inputparser = argparse.ArgumentParser()
         inputparser.add_argument("PREFILE", help="Font file path/URL 1")
@@ -105,12 +112,16 @@ def run(argv):
     #  File path argument validations
     # -------------------------------
 
-    if not inputs.PREFILE.startswith("http") and not file_exists(inputs.PREFILE):
+    if not inputs.PREFILE.startswith("http") and not path_exists(
+        inputs.PREFILE, include_dir_paths=include_dir_paths
+    ):
         sys.stderr.write(
             f"[*] ERROR: The file path '{inputs.PREFILE}' can not be found.{os.linesep}"
         )
         sys.exit(1)
-    if not inputs.POSTFILE.startswith("http") and not file_exists(inputs.POSTFILE):
+    if not inputs.POSTFILE.startswith("http") and not path_exists(
+        inputs.POSTFILE, include_dir_paths=include_dir_paths
+    ):
         sys.stderr.write(
             f"[*] ERROR: The file path '{inputs.POSTFILE}' can not be found.{os.linesep}"
         )

lib/fdiff/utils.py

@@ -5,9 +5,13 @@
 from datetime import datetime, timezone
 
 
-def file_exists(path):
-    """Validates file path as existing local file"""
-    return os.path.exists(path)
+def path_exists(path, include_dir_paths=False):
+    """Validates existing paths.  The include_dir_paths parameter
+    toggles acceptance of dir paths in addition to file paths."""
+    if include_dir_paths:
+        return os.path.exists(path)
+    else:
+        return os.path.isfile(path)
 
 
 def get_file_modtime(path):

tests/test_utils.py

@@ -1,17 +1,40 @@
 import os
 import re
 
-from fdiff.utils import get_file_modtime, get_tables_argument_list, file_exists
+from fdiff.utils import get_file_modtime, get_tables_argument_list, path_exists
 
 import pytest
 
 
-def test_file_exists_true():
-    assert file_exists(os.path.join("tests", "testfiles", "test.txt")) is True
+def test_path_exists_default_true():
+    assert (
+        path_exists(
+            os.path.join("tests", "testfiles", "test.txt"), include_dir_paths=False
+        )
+        is True
+    )
 
 
-def test_file_exists_false():
-    assert file_exists(os.path.join("tests", "testfiles", "bogus.jpg")) is False
+def test_path_exists_default_false():
+    assert (
+        path_exists(
+            os.path.join("tests", "testfiles", "bogus.jpg"), include_dir_paths=False
+        )
+        is False
+    )
+
+
+def test_path_exists_default_dirpath_fails():
+    assert (
+        path_exists(os.path.join("tests", "testfiles"), include_dir_paths=False)
+        is False
+    )
+
+
+def test_path_exists_default_dirpath_toggle_succeeds():
+    assert (
+        path_exists(os.path.join("tests", "testfiles"), include_dir_paths=True) is True
+    )
 
 
 def test_get_file_modtime():

tests/test_utils_unix_only.py

@@ -0,0 +1,13 @@
+import os
+import sys
+
+import pytest
+
+from fdiff.utils import path_exists
+
+if sys.platform.startswith("win"):
+    pytest.skip("skipping Unix only tests", allow_module_level=True)
+
+
+def test_path_exists_default_dirpath_toggle_succeeds():
+    assert path_exists("/dev/null", include_dir_paths=True) is True