new approach to the columns heuristic

Author: hjwp

pytest_icdiff.py

@@ -1,7 +1,14 @@
 # pylint: disable=inconsistent-return-statements
+import py
 from pprintpp import pformat
 import icdiff
 
+COLS = py.io.TerminalWriter().fullwidth  # pylint: disable=no-member
+MARGIN_L = 9
+GUTTER = 2
+MARGINS = MARGIN_L + GUTTER + 1
+
+
 
 def pytest_assertrepr_compare(config, op, left, right):
     if op != '==':
@@ -13,26 +20,23 @@ def pytest_assertrepr_compare(config, op, left, right):
     except TypeError:
         pass
 
-    terminal_writer = config.get_terminal_writer()
-    cols = terminal_writer.fullwidth - 12
-
-    wide_left = pformat(left, indent=2, width=cols / 2).splitlines()
-    wide_right = pformat(right, indent=2, width=cols / 2).splitlines()
-    if len(wide_left) < 3 or len(wide_right) < 3:
-        shortest_left = pformat(left, indent=2, width=1).splitlines()
-        shortest_right = pformat(right, indent=2, width=1).splitlines()
-        longest_line_length = max(len(l) for l in shortest_left + shortest_right)
-    else:
-        longest_line_length = max(len(l) for l in wide_left + wide_right)
-    cols = int(min(longest_line_length, cols))
+    half_cols = COLS / 2 - MARGINS
 
-    pretty_left = pformat(left, indent=2, width=cols / 2).splitlines()
-    pretty_right = pformat(right, indent=2, width=cols / 2).splitlines()
+    pretty_left = pformat(left, indent=2, width=half_cols).splitlines()
+    pretty_right = pformat(right, indent=2, width=half_cols).splitlines()
+    diff_cols = COLS - MARGINS
 
+    if len(pretty_left) < 3 or len(pretty_right) < 3:
+        # avoid small diffs far apart by smooshing them up to the left
+        pretty_left = pformat(left, indent=2, width=1).splitlines()
+        pretty_right = pformat(right, indent=2, width=1).splitlines()
+        diff_cols = max(len(l) + 1 for l in pretty_left + pretty_right) * 2
+        if (diff_cols + MARGINS) > COLS:
+            diff_cols = COLS - MARGINS
 
-    differ = icdiff.ConsoleDiff(cols=cols + 12, tabsize=2)
+    differ = icdiff.ConsoleDiff(cols=diff_cols, tabsize=2)
 
-    if not terminal_writer.hasmarkup:
+    if not config.get_terminal_writer().hasmarkup:
         # colorization is disabled in Pytest - either due to the terminal not
         # supporting it or the user disabling it. We should obey, but there is
         # no option in icdiff to disable it, so we replace its colorization
@@ -44,4 +48,4 @@ def pytest_assertrepr_compare(config, op, left, right):
 
     icdiff_lines = list(differ.make_table(pretty_left, pretty_right))
 
-    return ['equals failed'] + [color_off + l for l in icdiff_lines]
+    return [f'equals failed'] + [color_off + l for l in icdiff_lines]

tests/test_pytest_icdiff.py

@@ -24,7 +24,7 @@ def test_one():
             assert {one!r} == {two!r}
         """
     )
-    output = testdir.runpytest().stdout.str()
+    output = testdir.runpytest('-vv').stdout.str()
     print(repr(output))
     two_left = "'the number two'"
     two_right = "'the number three'"
@@ -173,7 +173,7 @@ def test_one():
             assert {one!r} == {two!r}
         """
     )
-    output = testdir.runpytest().stdout.str()
+    output = testdir.runpytest('-vv').stdout.str()
     print(repr(output))
     assert re.search(r"1: '1',\s+$", output, flags=re.MULTILINE)
 
@@ -218,4 +218,35 @@ def test_one():
         if "hell" in l
         and "assert" not in l
     )
-    assert comparison_line.count('hell') < 13
+    assert comparison_line.count('hell') < 15
+
+
+def test_columns_are_calculated_outside_hook(testdir):
+    """
+    ok for some reason if you get the TerminalWriter width
+    inside of the hook it just always returns 80.
+    but (bear with me here) if you monkeypatch.setenv(COLUMNS)
+    then it _does_ affect the width inside the hook
+    (which is where we don't want to measure it)
+    but it does _not_ affect the one outside the hook
+    (which is the one we want to use).
+    """
+    left = "hello " * 10
+    right = "hella " * 10
+    testdir.makepyfile(
+        f"""
+        def test_one():
+            assert {left!r} == {right!r}
+        """
+    )
+    testdir.monkeypatch.setenv('COLUMNS', '50')
+    # testdir._method = 'subprocess'
+    output = testdir.runpytest(
+        '-vv', '--color=yes',
+    ).stdout.str()
+    comparison_line = next(
+        l for l in output.splitlines()
+        if 'hell' in l and "assert" not in l
+    )
+    assert comparison_line.count('hell') > 5
+