[__main__] add support for head and tail in fdiff executable

adds new --head and --tail options that take integer argument for number of lines

Author: chrissimpkins

lib/fdiff/__main__.py

@@ -8,6 +8,7 @@
 from fdiff import __version__
 from fdiff.color import color_unified_diff_line
 from fdiff.diff import u_diff
+from fdiff.textiter import head, tail
 from fdiff.utils import file_exists, get_tables_argument_list
 
 
@@ -59,6 +60,16 @@ def run(argv):
         default=None,
         help="Comma separated list of tables to exclude",
     )
+    parser.add_argument(
+        "--head",
+        type=int,
+        help="Display first n lines of output"
+    )
+    parser.add_argument(
+        "--tail",
+        type=int,
+        help="Display last n lines of output"
+    )
     parser.add_argument("PREFILE", help="Font file path 1")
     parser.add_argument("POSTFILE", help="Font file path 2")
 
@@ -129,9 +140,18 @@ def run(argv):
         )
         sys.exit(1)
 
+    # re-define the line contents of the diff iterable
+    # if head or tail is requested
+    if args.head:
+        iterable = head(diff, args.head)
+    elif args.tail:
+        iterable = tail(diff, args.tail)
+    else:
+        iterable = diff
+
     # print unified diff results to standard output stream
     if args.color:
-        for line in diff:
+        for line in iterable:
             sys.stdout.write(color_unified_diff_line(line))
     else:
-        sys.stdout.writelines(diff)
+        sys.stdout.writelines(iterable)

tests/test_main.py

@@ -251,3 +251,55 @@ def test_main_exclude_with_bad_table_definition_in_multi_table_request(capsys):
         captured = capsys.readouterr()
         assert captured.error.startswith("[*] ERROR:")
         assert exit_info.value.code == 1
+
+
+def test_main_head_request(capsys):
+    args = ["--head", "4", ROBOTO_BEFORE_PATH, ROBOTO_AFTER_PATH]
+
+    run(args)
+    captured = capsys.readouterr()
+    res_string_list = captured.out.split("\n")
+
+    # includes a newline at the end of the last line of output
+    # which makes the total # of lines in the list == n + 1
+    assert len(res_string_list) == 5
+
+    # have to handle the tests for the top two file path lines
+    # differently than the rest of the comparisons because
+    # the time is defined using local platform settings
+    # which makes tests fail on different remote CI testing services
+    for x, line in enumerate(res_string_list):
+        # treat top two lines of the diff as comparison of first 10 chars only
+        if x in (0, 1):
+            assert "tests/testfiles/Roboto-Regular.subset" in line
+        elif x == 2:
+            assert line == "@@ -4,34 +4,34 @@"
+        elif x == 3:
+            assert line == "   <GlyphOrder>"
+        else:
+            assert line == ""
+
+
+def test_main_tail_request(capsys):
+    args = ["--tail", "2", ROBOTO_BEFORE_PATH, ROBOTO_AFTER_PATH]
+
+    run(args)
+    captured = capsys.readouterr()
+    res_string_list = captured.out.split("\n")
+
+    # includes a newline at the end of the last line of output
+    # which makes the total # of lines in the list == n + 1
+    assert len(res_string_list) == 3
+
+    # have to handle the tests for the top two file path lines
+    # differently than the rest of the comparisons because
+    # the time is defined using local platform settings
+    # which makes tests fail on different remote CI testing services
+    for x, line in enumerate(res_string_list):
+        # treat top two lines of the diff as comparison of first 10 chars only
+        if x == 0:
+            assert line == "       </Lookup>"
+        elif x == 1:
+            assert line == "     </LookupList>"
+        else:
+            assert line == ""