Intermediate changes

commit_hash:5e2a2254279501ad2bde571fbd53c1a27a00e898

5 files changed, 813 insertions, 0 deletions

diff --git a/contrib/python/fonttools/fontTools/diff/__init__.py b/contrib/python/fonttools/fontTools/diff/__init__.py
new file mode 100644
index 00000000000..b876520b2a6
--- /dev/null
+++ b/contrib/python/fonttools/fontTools/diff/__init__.py
@@ -0,0 +1,441 @@
+import argparse
+import os
+import sys
+import shutil
+import subprocess
+from typing import Iterable, Iterator, List, Optional, Text, Tuple
+
+from .color import color_unified_diff_line
+from .diff import run_external_diff, u_diff
+from .utils import file_exists, get_tables_argument_list
+
+
+def pipe_output(output: str) -> None:
+    """Pipes output to a pager if stdout is a TTY and a pager is available."""
+
+    if not output:
+        return
+
+    if not sys.stdout.isatty():
+        sys.stdout.write(output)
+        return
+
+    pager = os.getenv("PAGER") or shutil.which("less")
+
+    if not pager:
+        sys.stdout.write(output)
+        return
+
+    pager_cmd = [pager]
+    if "less" in os.path.basename(pager):
+        pager_cmd.append("-R")
+
+    proc = subprocess.Popen(pager_cmd, stdin=subprocess.PIPE, text=True)
+    try:
+        proc.stdin.write(output)
+        proc.stdin.close()
+        proc.wait()
+    except (BrokenPipeError, KeyboardInterrupt):
+        # Pager process was terminated before all output was written.
+        # This is not an error. The main exception handler will deal with it.
+        if proc.stdin:
+            proc.stdin.close()
+        # The process might still be running, but we have closed our side of the
+        # pipe. The Popen destructor will send a SIGKILL to the child.
+    except Exception:
+        if proc.stdin:
+            proc.stdin.close()
+        raise
+
+
+def _is_gnu_diff(diff_tool: str) -> bool:
+    """Returns True if the provided diff executable is GNU diff."""
+    try:
+        proc = subprocess.run(
+            [diff_tool, "--version"],
+            stdout=subprocess.PIPE,
+            stderr=subprocess.PIPE,
+            text=True,
+        )
+    except OSError:
+        return False
+
+    version_output = (proc.stdout or "") + (proc.stderr or "")
+    return "GNU diffutils" in version_output
+
+
+def _iter_filtered_table_tags(
+    tags: Iterable[str],
+    include_tables: Optional[List[str]] = None,
+    exclude_tables: Optional[List[str]] = None,
+) -> Iterator[str]:
+    for tag in tags:
+        if exclude_tables and tag in exclude_tables:
+            continue
+        if include_tables and tag not in include_tables:
+            continue
+        yield tag
+
+
+def summarize(
+    file1: str,
+    file2: str,
+    include_tables: Optional[List[str]] = None,
+    exclude_tables: Optional[List[str]] = None,
+    font_number_1: int = -1,
+    font_number_2: int = -1,
+) -> Tuple[bool, str]:
+    from fontTools.ttLib import TTFont
+
+    with (
+        TTFont(file1, lazy=True, fontNumber=font_number_1) as font1,
+        TTFont(file2, lazy=True, fontNumber=font_number_2) as font2,
+    ):
+        tags1 = {str(tag) for tag in font1.reader.keys()}
+        tags2 = {str(tag) for tag in font2.reader.keys()}
+
+        all_tags = sorted(
+            set(
+                _iter_filtered_table_tags(
+                    tags1 | tags2,
+                    include_tables=include_tables,
+                    exclude_tables=exclude_tables,
+                )
+            )
+        )
+
+        only1 = [tag for tag in all_tags if tag in tags1 and tag not in tags2]
+        only2 = [tag for tag in all_tags if tag in tags2 and tag not in tags1]
+        both = [tag for tag in all_tags if tag in tags1 and tag in tags2]
+
+        identical = True
+        lines: List[str] = []
+
+        lines.append(f"Binary table summary:\n")
+        lines.append(f"  file1: {file1}\n")
+        lines.append(f"  file2: {file2}\n")
+
+        if only1:
+            identical = False
+            lines.append(f"\nTables only in file1 ({len(only1)}):\n")
+            for tag in only1:
+                lines.append(f"- {tag} ({len(font1.reader[tag])} bytes)\n")
+        if only2:
+            identical = False
+            lines.append(f"\nTables only in file2 ({len(only2)}):\n")
+            for tag in only2:
+                lines.append(f"+ {tag} ({len(font2.reader[tag])} bytes)\n")
+
+        lines.append(f"\nTables in both ({len(both)}):\n")
+        for tag in both:
+            data1 = font1.reader[tag]
+            data2 = font2.reader[tag]
+            if data1 == data2:
+                lines.append(f"  {tag}: SAME ({len(data1)} bytes)\n")
+            else:
+                identical = False
+                lines.append(f"* {tag}: DIFF ({len(data1)} vs {len(data2)} bytes)\n")
+
+        if identical:
+            lines.append("\nResult: SAME\n")
+        else:
+            lines.append("\nResult: DIFFERENT\n")
+
+        return identical, "".join(lines)
+
+
+def get_binary_exclude_tables(
+    file1: str,
+    file2: str,
+    include_tables: Optional[List[str]] = None,
+    exclude_tables: Optional[List[str]] = None,
+    font_number_1: int = -1,
+    font_number_2: int = -1,
+) -> Tuple[bool, str]:
+    from fontTools.ttLib import TTFont
+
+    with (
+        TTFont(file1, lazy=True, fontNumber=font_number_1) as font1,
+        TTFont(file2, lazy=True, fontNumber=font_number_2) as font2,
+    ):
+        tags1 = {str(tag) for tag in font1.reader.keys()}
+        tags2 = {str(tag) for tag in font2.reader.keys()}
+
+        all_tags = sorted(
+            set(
+                _iter_filtered_table_tags(
+                    tags1 | tags2,
+                    include_tables=include_tables,
+                    exclude_tables=exclude_tables,
+                )
+            )
+        )
+
+        both = [tag for tag in all_tags if tag in tags1 and tag in tags2]
+        out = set()
+
+        for tag in both:
+            data1 = font1.reader[tag]
+            data2 = font2.reader[tag]
+            if data1 == data2:
+                out.add(tag)
+
+        return out
+
+
+def main():
+    """Compare two fonts for differences"""
+    # try/except block rationale:
+    # handles "premature" socket closure exception that is
+    # raised by Python when stdout is piped to tools like
+    # the `head` executable and socket is closed early
+    # see: https://docs.python.org/3/library/signal.html#note-on-sigpipe
+    ret = 0
+    try:
+        ret = run(sys.argv[1:])
+    except KeyboardInterrupt:
+        pass
+    except BrokenPipeError:
+        # Python flushes standard streams on exit; redirect remaining output
+        # to devnull to avoid another BrokenPipeError at shutdown
+        devnull = os.open(os.devnull, os.O_WRONLY)
+        os.dup2(devnull, sys.stdout.fileno())
+    return ret
+
+
+def run(argv: List[Text]):
+    # ------------------------------------------
+    # argparse command line argument definitions
+    # ------------------------------------------
+    parser = argparse.ArgumentParser(
+        description="An OpenType table diff tool for fonts."
+    )
+    parser.add_argument(
+        "-l",
+        "--summary",
+        action="store_true",
+        help="Report table presence and binary equality only",
+    )
+    parser.add_argument(
+        "-U",
+        "--lines",
+        type=int,
+        default=3,
+        help="Number of context lines for unified diff (default: 3)",
+    )
+    parser.add_argument(
+        "-t",
+        "--include",
+        type=str,
+        nargs="+",
+        default=None,
+        help="Font tables to include. Multiple options are allowed.",
+    )
+    parser.add_argument(
+        "-x",
+        "--exclude",
+        type=str,
+        nargs="+",
+        default=None,
+        help="Font tables to exclude. Multiple options are allowed.",
+    )
+    parser.add_argument(
+        "--diff", type=str, help="Run external diff tool command (default: diff)"
+    )
+    parser.add_argument(
+        "--diff-arg",
+        type=str,
+        default=None,
+        help="External diff tool arguments (default: -u)",
+    )
+    parser.add_argument(
+        "--color",
+        choices=["auto", "never", "always"],
+        default="auto",
+        help="Whether to colorize output (default: auto)",
+    )
+    parser.add_argument(
+        "--y1",
+        type=int,
+        default=-1,
+        metavar="NUMBER",
+        help="Select font number for TrueType Collection (.ttc/.otc) FILE1, starting from 0",
+    )
+    parser.add_argument(
+        "--y2",
+        type=int,
+        default=-1,
+        metavar="NUMBER",
+        help="Select font number for TrueType Collection (.ttc/.otc) FILE2, starting from 0",
+    )
+    parser.add_argument(
+        "-a",
+        "--always",
+        action="store_true",
+        help="Compare tables even if binary identical",
+    )
+    parser.add_argument(
+        "-b",
+        "--binary",
+        action="store_true",
+        help="Compare tables only if binaries differ (default)",
+    )
+    parser.add_argument(
+        "-q", "--quiet", action="store_true", help="Suppress all output"
+    )
+    parser.add_argument("FILE1", help="Font file path 1")
+    parser.add_argument("FILE2", help="Font file path 2")
+
+    args: argparse.Namespace = parser.parse_args(argv)
+
+    # /////////////////////////////////////////////////////////
+    #
+    #  Validations
+    #
+    # /////////////////////////////////////////////////////////
+
+    # ----------------------------------
+    #  Incompatible argument validations
+    # ----------------------------------
+
+    if args.always and args.binary:
+        if not args.quiet:
+            sys.stderr.write(
+                f"[*] Error: --always and --binary are mutually exclusive options. "
+                f"Please use ONLY one of these options in your command.{os.linesep}"
+            )
+        return 2
+    if not args.always:
+        args.binary = True
+
+    # -------------------------------
+    #  File path argument validations
+    # -------------------------------
+
+    if not file_exists(args.FILE1):
+        if not args.quiet:
+            sys.stderr.write(
+                f"[*] ERROR: The file path '{args.FILE1}' can not be found.{os.linesep}"
+            )
+        return 2
+    if not file_exists(args.FILE2):
+        if not args.quiet:
+            sys.stderr.write(
+                f"[*] ERROR: The file path '{args.FILE2}' can not be found.{os.linesep}"
+            )
+        return 2
+
+    # /////////////////////////////////////////////////////////
+    #
+    #  Command line logic
+    #
+    # /////////////////////////////////////////////////////////
+
+    # parse explicitly included or excluded tables in
+    # the command line arguments
+    # set as a Python list if it was defined on the command line
+    # or as None if it was not set on the command line
+    include_list: Optional[List[Text]] = get_tables_argument_list(args.include)
+    exclude_list: Optional[List[Text]] = get_tables_argument_list(args.exclude)
+
+    if args.summary:
+        try:
+            identical, output = summarize(
+                args.FILE1,
+                args.FILE2,
+                include_tables=include_list,
+                exclude_tables=exclude_list,
+                font_number_1=args.y1,
+                font_number_2=args.y2,
+            )
+            if not args.quiet:
+                sys.stdout.write(output)
+            return 0 if identical else 1
+        except Exception as e:
+            if not args.quiet:
+                sys.stderr.write(f"[*] ERROR: {e}{os.linesep}")
+            return 2
+
+    if args.binary:
+        excluded_binary_tables = get_binary_exclude_tables(
+            args.FILE1,
+            args.FILE2,
+            include_tables=include_list,
+            exclude_tables=exclude_list,
+            font_number_1=args.y1,
+            font_number_2=args.y2,
+        )
+        if include_list is not None:
+            include_list = [
+                tag for tag in include_list if tag not in excluded_binary_tables
+            ]
+        else:
+            if exclude_list is None:
+                exclude_list = []
+            exclude_list.extend(sorted(excluded_binary_tables))
+
+    diff_tool = args.diff
+    color_output = args.color == "always" or (
+        args.color == "auto" and sys.stdout.isatty
+    )
+
+    if diff_tool is None:
+        diff_tool = shutil.which("diff")
+    elif diff_tool:
+        diff_tool = shutil.which(diff_tool)
+        if diff_tool is None:
+            if not args.quiet:
+                sys.stderr.write(
+                    f"[*] ERROR: The external diff tool executable "
+                    f"'{args.diff}' was not found.{os.linesep}"
+                )
+            return 2
+
+    try:
+        if diff_tool:
+            diff_arg = args.diff_arg
+            if diff_arg is None:
+                if args.lines == 3:
+                    diff_arg = ["-u"]
+                else:
+                    diff_arg = ["-u{}".format(args.lines)]
+                if _is_gnu_diff(diff_tool):
+                    diff_arg.append(r"-F^\s\s<")
+            else:
+                diff_arg = diff_arg.split()
+
+            output = run_external_diff(
+                diff_tool,
+                diff_arg,
+                args.FILE1,
+                args.FILE2,
+                include_tables=include_list,
+                exclude_tables=exclude_list,
+                font_number_a=args.y1,
+                font_number_b=args.y2,
+                use_multiprocess=True,
+            )
+        else:
+            output = u_diff(
+                args.FILE1,
+                args.FILE2,
+                context_lines=args.lines,
+                include_tables=include_list,
+                exclude_tables=exclude_list,
+                font_number_a=args.y1,
+                font_number_b=args.y2,
+                use_multiprocess=True,
+            )
+
+        if color_output:
+            output = [color_unified_diff_line(line) for line in output]
+
+        output = "".join(output)
+        if not args.quiet:
+            pipe_output(output)
+        return 1 if output else 0
+
+    except Exception as e:
+        if not args.quiet:
+            sys.stderr.write(f"[*] ERROR: {e}{os.linesep}")
+        return 2
diff --git a/contrib/python/fonttools/fontTools/diff/__main__.py b/contrib/python/fonttools/fontTools/diff/__main__.py
new file mode 100644
index 00000000000..8dbef1dfc5d
--- /dev/null
+++ b/contrib/python/fonttools/fontTools/diff/__main__.py
@@ -0,0 +1,6 @@
+import sys
+from fontTools.diff import main
+
+
+if __name__ == "__main__":
+    sys.exit(main())
diff --git a/contrib/python/fonttools/fontTools/diff/color.py b/contrib/python/fonttools/fontTools/diff/color.py
new file mode 100644
index 00000000000..e6ef489d67e
--- /dev/null
+++ b/contrib/python/fonttools/fontTools/diff/color.py
@@ -0,0 +1,44 @@
+from typing import Dict, Text
+
+ansicolors: Dict[Text, Text] = {
+    "BLACK": "\033[30m",
+    "RED": "\033[31m",
+    "GREEN": "\033[32m",
+    "YELLOW": "\033[33m",
+    "BLUE": "\033[34m",
+    "MAGENTA": "\033[35m",
+    "CYAN": "\033[36m",
+    "WHITE": "\033[37m",
+    "BOLD": "\033[1m",
+    "RESET": "\033[0m",
+}
+
+green_start: Text = ansicolors["GREEN"]
+red_start: Text = ansicolors["RED"]
+cyan_start: Text = ansicolors["CYAN"]
+reset: Text = ansicolors["RESET"]
+
+
+def color_unified_diff_line(line: Text) -> Text:
+    """Returns an ANSI escape code colored string with color based
+    on the unified diff line type."""
+    if line[0:2] == "+ ":
+        return f"{green_start}{line}{reset}"
+    elif line == "+\n":
+        # some lines are formatted as hyphen only with no other characters
+        # this indicates an added empty line
+        return f"{green_start}{line}{reset}"
+    elif line[0:2] == "- ":
+        return f"{red_start}{line}{reset}"
+    elif line == "-\n":
+        # some lines are formatted as hyphen only with no other characters
+        # this indicates a deleted empty line
+        return f"{red_start}{line}{reset}"
+    elif line[0:3] == "@@ ":
+        return f"{cyan_start}{line}{reset}"
+    elif line[0:4] == "--- ":
+        return f"{red_start}{line}{reset}"
+    elif line[0:4] == "+++ ":
+        return f"{green_start}{line}{reset}"
+    else:
+        return line
diff --git a/contrib/python/fonttools/fontTools/diff/diff.py b/contrib/python/fonttools/fontTools/diff/diff.py
new file mode 100644
index 00000000000..302f2e677ae
--- /dev/null
+++ b/contrib/python/fonttools/fontTools/diff/diff.py
@@ -0,0 +1,294 @@
+import os
+import subprocess
+import tempfile
+from contextlib import contextmanager
+from difflib import unified_diff
+from multiprocessing import Pool, cpu_count
+from typing import Any, Callable, Iterable, Iterator, List, Optional, Text, Tuple
+
+from fontTools.ttLib import TTFont  # type: ignore
+
+from .utils import get_file_modtime
+
+#
+#
+#  Private functions
+#
+#
+
+
+def _get_fonts_and_save_xml(
+    filepath_a: Text,
+    filepath_b: Text,
+    tmpdirpath: Text,
+    include_tables: Optional[List[Text]],
+    exclude_tables: Optional[List[Text]],
+    font_number_a: int,
+    font_number_b: int,
+    use_multiprocess: bool,
+) -> Tuple[Text, Text, Text, Text, Text, Text]:
+    post_pathname, postpath, pre_pathname, prepath = _get_pre_post_paths(
+        filepath_a, filepath_b
+    )
+    # instantiate left and right fontTools.ttLib.TTFont objects
+    tt_left = TTFont(prepath, fontNumber=font_number_a)
+    tt_right = TTFont(postpath, fontNumber=font_number_b)
+    left_ttxpath = os.path.join(tmpdirpath, "left.ttx")
+    right_ttxpath = os.path.join(tmpdirpath, "right.ttx")
+    _mp_save_ttx_xml(
+        tt_left,
+        tt_right,
+        left_ttxpath,
+        right_ttxpath,
+        exclude_tables,
+        include_tables,
+        use_multiprocess,
+    )
+    return left_ttxpath, right_ttxpath, pre_pathname, prepath, post_pathname, postpath
+
+
+def _get_pre_post_paths(
+    filepath_a: Text,
+    filepath_b: Text,
+) -> Tuple[Text, Text, Text, Text]:
+    prepath = filepath_a
+    postpath = filepath_b
+    pre_pathname = filepath_a
+    post_pathname = filepath_b
+    return post_pathname, postpath, pre_pathname, prepath
+
+
+def _mp_save_ttx_xml(
+    tt_left: Any,
+    tt_right: Any,
+    left_ttxpath: Text,
+    right_ttxpath: Text,
+    exclude_tables: Optional[List[Text]],
+    include_tables: Optional[List[Text]],
+    use_multiprocess: bool,
+) -> None:
+    if use_multiprocess and cpu_count() > 1:
+        # Use parallel fontTools.ttLib.TTFont.saveXML dump
+        # by default on multi CPU systems.  This is a performance
+        # optimization. Profiling demonstrates that this can reduce
+        # execution time by up to 30% for some fonts
+        mp_args_list = [
+            (tt_left, left_ttxpath, include_tables, exclude_tables),
+            (tt_right, right_ttxpath, include_tables, exclude_tables),
+        ]
+        with Pool(processes=2) as pool:
+            pool.starmap(_ttfont_save_xml, mp_args_list)
+    else:
+        # use sequential fontTools.ttLib.TTFont.saveXML dumps
+        # when use_multiprocess is False or single CPU system
+        # detected
+        _ttfont_save_xml(tt_left, left_ttxpath, include_tables, exclude_tables)
+        _ttfont_save_xml(tt_right, right_ttxpath, include_tables, exclude_tables)
+
+
+def _ttfont_save_xml(
+    ttf: Any,
+    filepath: Text,
+    include_tables: Optional[List[Text]],
+    exclude_tables: Optional[List[Text]],
+) -> bool:
+    """Writes TTX specification formatted XML to disk on filepath."""
+    ttf.saveXML(filepath, tables=include_tables, skipTables=exclude_tables)
+    return True
+
+
+@contextmanager
+def _saved_ttx_files(
+    filepath_a: Text,
+    filepath_b: Text,
+    include_tables: Optional[List[Text]],
+    exclude_tables: Optional[List[Text]],
+    font_number_a: int,
+    font_number_b: int,
+    use_multiprocess: bool,
+) -> Iterator[Tuple[Text, Text, Text, Text, Text, Text]]:
+    with tempfile.TemporaryDirectory() as tmpdirpath:
+        yield _get_fonts_and_save_xml(
+            filepath_a,
+            filepath_b,
+            tmpdirpath,
+            include_tables,
+            exclude_tables,
+            font_number_a,
+            font_number_b,
+            use_multiprocess,
+        )
+
+
+def _diff_with_saved_ttx_files(
+    filepath_a: Text,
+    filepath_b: Text,
+    include_tables: Optional[List[Text]],
+    exclude_tables: Optional[List[Text]],
+    font_number_a: int,
+    font_number_b: int,
+    use_multiprocess: bool,
+    create_differ: Callable[[Text, Text, Text, Text, Text, Text], Iterable[Text]],
+) -> Iterator[Text]:
+    with _saved_ttx_files(
+        filepath_a,
+        filepath_b,
+        include_tables,
+        exclude_tables,
+        font_number_a,
+        font_number_b,
+        use_multiprocess,
+    ) as (
+        left_ttxpath,
+        right_ttxpath,
+        pre_pathname,
+        prepath,
+        post_pathname,
+        postpath,
+    ):
+        yield from create_differ(
+            left_ttxpath,
+            right_ttxpath,
+            pre_pathname,
+            prepath,
+            post_pathname,
+            postpath,
+        )
+
+
+#
+#
+#  Public functions
+#
+#
+
+
+def u_diff(
+    filepath_a: Text,
+    filepath_b: Text,
+    context_lines: int = 3,
+    include_tables: Optional[List[Text]] = None,
+    exclude_tables: Optional[List[Text]] = None,
+    font_number_a: int = -1,
+    font_number_b: int = -1,
+    use_multiprocess: bool = True,
+) -> Iterator[Text]:
+    """Performs a unified diff on a TTX serialized data format dump of font binary data using
+    a modified version of the Python standard libary difflib module.
+
+    filepath_a: (string) pre-file local file path
+    filepath_b: (string) post-file local file path
+    context_lines: (int) number of context lines to include in the diff (default=3)
+    include_tables: (list of str) Python list of OpenType tables to include in the diff
+    exclude_tables: (list of str) Python list of OpentType tables to exclude from the diff
+    use_multiprocess: (bool) use multi-processor optimizations (default=True)
+
+    include_tables and exclude_tables are mutually exclusive arguments.  Only one should
+    be defined
+
+    :returns: Generator of ordered diff line strings that include newline line endings
+    :raises: KeyError if include_tables or exclude_tables includes a mis-specified table
+    that is not included in filepath_a OR filepath_b
+    """
+
+    def _create_unified_diff(
+        left_ttxpath: Text,
+        right_ttxpath: Text,
+        pre_pathname: Text,
+        prepath: Text,
+        post_pathname: Text,
+        postpath: Text,
+    ) -> Iterable[Text]:
+        with open(left_ttxpath) as ff:
+            fromlines = ff.readlines()
+        with open(right_ttxpath) as tf:
+            tolines = tf.readlines()
+
+        fromdate = get_file_modtime(prepath)
+        todate = get_file_modtime(postpath)
+
+        yield from unified_diff(
+            fromlines,
+            tolines,
+            pre_pathname,
+            post_pathname,
+            fromdate,
+            todate,
+            n=context_lines,
+        )
+
+    yield from _diff_with_saved_ttx_files(
+        filepath_a,
+        filepath_b,
+        include_tables,
+        exclude_tables,
+        font_number_a,
+        font_number_b,
+        use_multiprocess,
+        _create_unified_diff,
+    )
+
+
+def run_external_diff(
+    diff_tool: Text,
+    diff_args: List[Text],
+    filepath_a: Text,
+    filepath_b: Text,
+    include_tables: Optional[List[Text]] = None,
+    exclude_tables: Optional[List[Text]] = None,
+    font_number_a: int = -1,
+    font_number_b: int = -1,
+    use_multiprocess: bool = True,
+) -> Iterator[Text]:
+    """Performs a unified diff on a TTX serialized data format dump of font binary data using
+    an external diff executable that is requested by the caller via `command`
+
+    diff_tool: (string) command line executable string
+    diff_args: (list of strings) arguments for the diff tool
+    filepath_a: (string) pre-file local file path
+    filepath_b: (string) post-file local file path
+    include_tables: (list of str) Python list of OpenType tables to include in the diff
+    exclude_tables: (list of str) Python list of OpentType tables to exclude from the diff
+    use_multiprocess: (bool) use multi-processor optimizations (default=True)
+
+    include_tables and exclude_tables are mutually exclusive arguments.  Only one should
+    be defined
+
+    :returns: Generator of ordered diff line strings that include newline line endings
+    :raises: KeyError if include_tables or exclude_tables includes a mis-specified table
+    that is not included in filepath_a OR filepath_b
+    :raises: IOError if exception raised during execution of `command` on TTX files
+    """
+
+    def _create_external_diff(
+        left_ttxpath: Text,
+        right_ttxpath: Text,
+        _pre_pathname: Text,
+        _prepath: Text,
+        _post_pathname: Text,
+        _postpath: Text,
+    ) -> Iterable[Text]:
+        command = [diff_tool] + diff_args + [left_ttxpath, right_ttxpath]
+        process = subprocess.Popen(
+            command,
+            stdout=subprocess.PIPE,
+            stderr=subprocess.PIPE,
+            encoding="utf8",
+        )
+
+        for line in process.stdout:
+            yield line
+        err = process.stderr.read()
+        if err:
+            raise IOError(err)
+
+    yield from _diff_with_saved_ttx_files(
+        filepath_a,
+        filepath_b,
+        include_tables,
+        exclude_tables,
+        font_number_a,
+        font_number_b,
+        use_multiprocess,
+        _create_external_diff,
+    )
diff --git a/contrib/python/fonttools/fontTools/diff/utils.py b/contrib/python/fonttools/fontTools/diff/utils.py
new file mode 100644
index 00000000000..aed97063636
--- /dev/null
+++ b/contrib/python/fonttools/fontTools/diff/utils.py
@@ -0,0 +1,28 @@
+import os
+from datetime import datetime, timezone
+from typing import List, Optional, Text, Union
+
+
+def file_exists(path: Union[bytes, str, "os.PathLike[Text]"]) -> bool:
+    """Validates file path as existing local file"""
+    return os.path.isfile(path)
+
+
+def get_file_modtime(path: Union[bytes, str, "os.PathLike[Text]"]) -> Text:
+    """Returns ISO formatted file modification time in local system timezone"""
+    return (
+        datetime.fromtimestamp(os.stat(path).st_mtime, timezone.utc)
+        .astimezone()
+        .isoformat()
+    )
+
+
+def get_tables_argument_list(table_list: Optional[List[Text]]) -> Optional[List[Text]]:
+    """Converts a list of OpenType table string into a Python list or
+    return None if the table_list was not defined (i.e., it was not included
+    in an option on the command line). Tables that are composed of three
+    characters must be right padded with a space."""
+    if table_list is None:
+        return None
+    else:
+        return [table.ljust(4) for table in table_list]