Revert datetime usetex ticklabels to use default tex font.

anntzer · anntzer · commit 473f2095f1fd · 2022-01-31T08:04:04.000+01:00
with `{\fontfamily{\familydefault}\selectfont ...}`, instead of using
math and selectively escaping parts of the string.

Note that this is only possible now that tex strings are passed "all at
once" to the tex process rather than "one line at a time", because if
breaking at `"\n"` as previously done, then the braces of the tex
command above would become unbalanced (and lines other than the first
would not see the `\selectfont`).

The main difference in rendering is that hyphens (e.g. in YY-MM-DD) are
now rendered as plain hyphens rather than minus signs, but some googling
suggests that this is in fact correct (see e.g. ctan datetime2 or
isodate packages).  Also, month names are now rendered with serif, but
that seems more consistent with day and years which are also serifed
(and which were the original source of all these issues).

See also the script below, which reproduces the various issues raised
over the years:
```python
from datetime import datetime, timedelta
from matplotlib.dates import ConciseDateFormatter, DateFormatter
import matplotlib.pyplot as plt
import numpy as np

plt.rcdefaults(); plt.rcParams['text.usetex'] = True
fig, axs = plt.subplots(4, constrained_layout=True, figsize=(12, 4))
t0 = datetime.now()
ts = [t0 + i * timedelta(days=1) for i in range(10)]
axs[0].plot(ts, range(10))
axs[1].plot(ts, range(10))
axs[1].xaxis.set_major_formatter(ConciseDateFormatter(axs[1].xaxis.get_major_locator()))
ts = [t0 + i * timedelta(seconds=6) for i in range(100)]
axs[2].plot(ts, range(100))
axs[3].xaxis.set_major_formatter(DateFormatter('%d/%m\n%Y'))

plt.show()
```
diff --git a/lib/matplotlib/dates.py b/lib/matplotlib/dates.py
@@ -173,7 +173,6 @@
 import functools
 import logging
 import math
-import re
 
 from dateutil.rrule import (rrule, MO, TU, WE, TH, FR, SA, SU, YEARLY,
                             MONTHLY, WEEKLY, DAILY, HOURLY, MINUTELY,
@@ -605,16 +604,7 @@ def drange(dstart, dend, delta):
 
 
 def _wrap_in_tex(text):
-    p = r'([a-zA-Z]+)'
-    ret_text = re.sub(p, r'}$\1$\\mathdefault{', text)
-
-    # Braces ensure symbols are not spaced like binary operators.
-    ret_text = ret_text.replace('-', '{-}').replace(':', '{:}')
-    # To not concatenate space between numbers.
-    ret_text = ret_text.replace(' ', r'\;')
-    ret_text = '$\\mathdefault{' + ret_text + '}$'
-    ret_text = ret_text.replace('$\\mathdefault{}$', '')
-    return ret_text
+    return r"{\fontfamily{\familydefault}\selectfont " + text + "}"
 
 
 ## date tickers and formatters ###
diff --git a/lib/matplotlib/tests/test_dates.py b/lib/matplotlib/tests/test_dates.py
@@ -323,13 +323,13 @@ def callable_formatting_function(dates, _):
 
 @pytest.mark.parametrize('delta, expected', [
     (datetime.timedelta(weeks=52 * 200),
-     [r'$\mathdefault{%d}$' % year for year in range(1990, 2171, 20)]),
+     range(1990, 2171, 20)),
     (datetime.timedelta(days=30),
-     [r'$\mathdefault{1990{-}01{-}%02d}$' % day for day in range(1, 32, 3)]),
+     ['1990-01-%02d' % day for day in range(1, 32, 3)]),
     (datetime.timedelta(hours=20),
-     [r'$\mathdefault{01{-}01\;%02d}$' % hour for hour in range(0, 21, 2)]),
+     ['01-01 %02d' % hour for hour in range(0, 21, 2)]),
     (datetime.timedelta(minutes=10),
-     [r'$\mathdefault{01\;00{:}%02d}$' % minu for minu in range(0, 11)]),
+     ['01 00:%02d' % minu for minu in range(0, 11)]),
 ])
 def test_date_formatter_usetex(delta, expected):
     style.use("default")
@@ -342,7 +342,8 @@ def test_date_formatter_usetex(delta, expected):
     locator.axis.set_view_interval(mdates.date2num(d1), mdates.date2num(d2))
 
     formatter = mdates.AutoDateFormatter(locator, usetex=True)
-    assert [formatter(loc) for loc in locator()] == expected
+    assert [formatter(loc) for loc in locator()] == [
+        r'{\fontfamily{\familydefault}\selectfont %s}' % s for s in expected]
 
 
 def test_drange():
@@ -637,24 +638,14 @@ def test_offset_changes():
 
 @pytest.mark.parametrize('t_delta, expected', [
     (datetime.timedelta(weeks=52 * 200),
-     ['$\\mathdefault{%d}$' % (t, ) for t in range(1980, 2201, 20)]),
+     range(1980, 2201, 20)),
     (datetime.timedelta(days=40),
-     ['Jan', '$\\mathdefault{05}$', '$\\mathdefault{09}$',
-      '$\\mathdefault{13}$', '$\\mathdefault{17}$', '$\\mathdefault{21}$',
-      '$\\mathdefault{25}$', '$\\mathdefault{29}$', 'Feb',
-      '$\\mathdefault{05}$', '$\\mathdefault{09}$']),
+     ['Jan', '05', '09', '13', '17', '21', '25', '29', 'Feb', '05', '09']),
     (datetime.timedelta(hours=40),
-     ['Jan$\\mathdefault{{-}01}$', '$\\mathdefault{04{:}00}$',
-      '$\\mathdefault{08{:}00}$', '$\\mathdefault{12{:}00}$',
-      '$\\mathdefault{16{:}00}$', '$\\mathdefault{20{:}00}$',
-      'Jan$\\mathdefault{{-}02}$', '$\\mathdefault{04{:}00}$',
-      '$\\mathdefault{08{:}00}$', '$\\mathdefault{12{:}00}$',
-      '$\\mathdefault{16{:}00}$']),
+     ['Jan-01', '04:00', '08:00', '12:00', '16:00', '20:00',
+      'Jan-02', '04:00', '08:00', '12:00', '16:00']),
     (datetime.timedelta(seconds=2),
-     ['$\\mathdefault{59.5}$', '$\\mathdefault{00{:}00}$',
-      '$\\mathdefault{00.5}$', '$\\mathdefault{01.0}$',
-      '$\\mathdefault{01.5}$', '$\\mathdefault{02.0}$',
-      '$\\mathdefault{02.5}$']),
+     ['59.5', '00:00', '00.5', '01.0', '01.5', '02.0', '02.5']),
 ])
 def test_concise_formatter_usetex(t_delta, expected):
     d1 = datetime.datetime(1997, 1, 1)
@@ -665,7 +656,8 @@ def test_concise_formatter_usetex(t_delta, expected):
     locator.axis.set_view_interval(mdates.date2num(d1), mdates.date2num(d2))
 
     formatter = mdates.ConciseDateFormatter(locator, usetex=True)
-    assert formatter.format_ticks(locator()) == expected
+    assert formatter.format_ticks(locator()) == [
+        r'{\fontfamily{\familydefault}\selectfont %s}' % s for s in expected]
 
 
 def test_concise_formatter_formats():
@@ -1326,3 +1318,9 @@ def test_concise_formatter_call():
 def test_date_ticker_factory(span, expected_locator):
     locator, _ = mdates.date_ticker_factory(span)
     assert isinstance(locator, expected_locator)
+
+
+def test_usetex_newline():
+    fig, ax = plt.subplots()
+    ax.xaxis.set_major_formatter(mdates.DateFormatter('%d/%m\n%Y'))
+    fig.canvas.draw()
