Remove the use_cmex font fallback mechanism.

anntzer · anntzer · commit b1691d986ddf · 2020-10-13T22:02:49.000+02:00
The `use_cmex` flag and `latex_to_cmex` table is a
fallback-to-computermodern mathtext system that is strictly less
powerful than the `mathtext.fallback_to_cm` (now `mathtext.fallback`)
system.  Also, the `latex_to_cmex` table was incomplete.

Previously, with something like
```
rcParams["mathtext.fontset"] = "custom"; figtext(.5, .5, r"$\leftangle\langle$")
```
`\leftangle` would get unconditionally replaced by a Computer Modern
glyph, whereas `\langle` would stay as DejaVu Sans (as DejaVu provides
that glyph).  With this patch, both glyphs now use DejaVu.

Conversely, if one forces the use of a font which does not contain the
`\langle` glyph (e.g. adding `rcParams["mathtext.rm"] = "Comic Sans
MS"`), then both `\leftangle` and `\langle` get substituted to use
Computer Modern; this is not changed by this PR (except that now *both*
fallbacks can be controlled by `rcParams["mathtext.fallback"]`.

`latex_to_cmex` and `use_cmex` were marked as deprecated, but with no
actual deprecation machinery as they can all go away once `mathtext`
fully goes private anyways.
diff --git a/lib/matplotlib/_mathtext.py b/lib/matplotlib/_mathtext.py
@@ -20,8 +20,7 @@
 import matplotlib as mpl
 from . import cbook
 from ._mathtext_data import (
-    latex_to_bakoma, latex_to_cmex, latex_to_standard, stix_virtual_fonts,
-    tex2uni)
+    latex_to_bakoma, latex_to_standard, stix_virtual_fonts, tex2uni)
 from .afm import AFM
 from .font_manager import FontProperties, findfont, get_font
 from .ft2font import KERNING_DEFAULT
@@ -452,7 +451,7 @@ class UnicodeFonts(TruetypeFonts):
     This class will "fallback" on the Bakoma fonts when a required
     symbol can not be found in the font.
     """
-    use_cmex = True
+    use_cmex = True  # Unused; delete once mathtext becomes private.
 
     def __init__(self, *args, **kwargs):
         # This must come first so the backend's owner is set correctly
@@ -497,22 +496,13 @@ def _map_virtual_font(self, fontname, font_class, uniindex):
         return fontname, uniindex
 
     def _get_glyph(self, fontname, font_class, sym, fontsize, math=True):
-        found_symbol = False
-
-        if self.use_cmex:
-            uniindex = latex_to_cmex.get(sym)
-            if uniindex is not None:
-                fontname = 'ex'
-                found_symbol = True
-
-        if not found_symbol:
-            try:
-                uniindex = get_unicode_index(sym, math)
-                found_symbol = True
-            except ValueError:
-                uniindex = ord('?')
-                _log.warning(
-                    "No TeX to unicode mapping for {!a}.".format(sym))
+        try:
+            uniindex = get_unicode_index(sym, math)
+            found_symbol = True
+        except ValueError:
+            uniindex = ord('?')
+            found_symbol = False
+            _log.warning("No TeX to unicode mapping for {!a}.".format(sym))
 
         fontname, uniindex = self._map_virtual_font(
             fontname, font_class, uniindex)
@@ -574,7 +564,7 @@ def get_sized_alternatives_for_symbol(self, fontname, sym):
 
 
 class DejaVuFonts(UnicodeFonts):
-    use_cmex = False
+    use_cmex = False  # Unused; delete once mathtext becomes private.
 
     def __init__(self, *args, **kwargs):
         # This must come first so the backend's owner is set correctly
@@ -677,7 +667,7 @@ class StixFonts(UnicodeFonts):
         4: 'STIXSizeFourSym',
         5: 'STIXSizeFiveSym',
     }
-    use_cmex = False
+    use_cmex = False  # Unused; delete once mathtext becomes private.
     cm_fallback = False
     _sans = False
 
diff --git a/lib/matplotlib/_mathtext_data.py b/lib/matplotlib/_mathtext_data.py
@@ -236,7 +236,7 @@
     '\\_'                        : ('cmtt10', 0x5f)
 }
 
-latex_to_cmex = {
+latex_to_cmex = {  # Unused; delete once mathtext becomes private.
     r'\__sqrt__'   : 112,
     r'\bigcap'     : 92,
     r'\bigcup'     : 91,

Original file line number	Diff line number	Diff line change
`@@ -236,7 +236,7 @@`
`236`	`236`	`'\\_' : ('cmtt10', 0x5f)`
`237`	`237`	`}`
`238`	`238`
`239`		`-latex_to_cmex = {`
	`239`	`+latex_to_cmex = { # Unused; delete once mathtext becomes private.`
`240`	`240`	`r'\__sqrt__' : 112,`
`241`	`241`	`r'\bigcap' : 92,`
`242`	`242`	`r'\bigcup' : 91,`