From 07455790b1b1369775b86672a41594c565d3698c Mon Sep 17 00:00:00 2001
From: Cosimo Lupo <clupo@google.com>
Date: Tue, 16 Nov 2021 12:59:05 +0000
Subject: [PATCH] simplify ranges() generator

---
 Lib/fontTools/subset/svg.py | 23 ++++++++++++++---------
 Tests/subset/svg_test.py    | 18 +++++++++++++++++-
 2 files changed, 31 insertions(+), 10 deletions(-)

diff --git a/Lib/fontTools/subset/svg.py b/Lib/fontTools/subset/svg.py
index 169a92ee3..08f552f0f 100644
--- a/Lib/fontTools/subset/svg.py
+++ b/Lib/fontTools/subset/svg.py
@@ -2,7 +2,7 @@ from __future__ import annotations
 
 import re
 from functools import lru_cache
-from itertools import chain, count, groupby
+from itertools import chain, count
 from typing import Dict, Iterable, Iterator, List, Optional, Set, Tuple
 
 try:
@@ -172,14 +172,19 @@ def update_glyph_href_links(svg: etree.Element, id_map: Dict[str, str]) -> None:
 
 
 def ranges(ints: Iterable[int]) -> Iterator[Tuple[int, int]]:
-    # Yield (min, max) ranges of consecutive integers from the input set
-    sorted_ints = sorted(set(ints))
-    # to group together consecutive ints, we use as 'key' the difference
-    # between their index in the (sorted) list and themselves, which stays
-    # the same for consecutive numbers
-    for _key, group in groupby(enumerate(sorted_ints), lambda i: i[0] - i[1]):
-        consecutive_ints = [v for _i, v in group]
-        yield (consecutive_ints[0], consecutive_ints[-1])
+    # Yield sorted, non-overlapping (min, max) ranges of consecutive integers
+    sorted_ints = iter(sorted(set(ints)))
+    try:
+        start = end = next(sorted_ints)
+    except StopIteration:
+        return
+    for v in sorted_ints:
+        if v - 1 == end:
+            end = v
+        else:
+            yield (start, end)
+            start = end = v
+    yield (start, end)
 
 
 @_add_method(ttLib.getTableClass("SVG "))
diff --git a/Tests/subset/svg_test.py b/Tests/subset/svg_test.py
index bdfc4d68c..919570139 100644
--- a/Tests/subset/svg_test.py
+++ b/Tests/subset/svg_test.py
@@ -6,7 +6,7 @@ from fontTools import subset
 from fontTools.fontBuilder import FontBuilder
 from fontTools.pens.ttGlyphPen import TTGlyphPen
 from fontTools.ttLib import TTFont, newTable
-from fontTools.subset.svg import NAMESPACES
+from fontTools.subset.svg import NAMESPACES, ranges
 
 import pytest
 
@@ -453,3 +453,19 @@ def test_subset_svg_missing_glyph(empty_svg_font, tmp_path):
     subset.main([str(svg_font_path), f"--output-file={subset_path}", f"--gids=2"])
 
     assert "SVG " not in TTFont(subset_path)
+
+
+@pytest.mark.parametrize(
+    "ints, expected_ranges",
+    [
+        ((), []),
+        ((0,), [(0, 0)]),
+        ((0, 1), [(0, 1)]),
+        ((1, 1, 1, 1), [(1, 1)]),
+        ((1, 3), [(1, 1), (3, 3)]),
+        ((4, 2, 1, 3), [(1, 4)]),
+        ((1, 2, 4, 5, 6, 9, 13, 14, 15), [(1, 2), (4, 6), (9, 9), (13, 15)]),
+    ],
+)
+def test_ranges(ints, expected_ranges):
+    assert list(ranges(ints)) == expected_ranges