gh-34995: Support for tachyon >= 0.99.2

    
Taken from #23712.

This is necessary to support tachyon >= 0.99.2, without losing support
for older versions of tachyon.

In case #23712 gets delayed, it'd be nice to include this so nothing
breaks if system tachyon is updated. This is the first commit from the
branch there which already had positive review (the actual update of
tachyon has an issue mentioned in
#23712 (comment).)

_From the commit log:_

In tachyon 0.99.2 the keyword `focallength` was changed to `focaldist`.
To support it, when running on version >= 0.99.2 we "patch" the model as
constructed by class `sage.plot.plot3d.tachyon.Tachyon`.

In the future (possibly when tachyon in sage gets upgraded), all the
focallength occurences in sage.plot.plot3d.tachyon can be replaced by
focaldist for consistency with new tachyon, and the logic here can be
reversed (i.e. patch the model when self.version() < '0.99.2') or just
drop support for old versions.
    
URL: #34995
Reported by: Gonzalo Tornaría
Reviewer(s): Matthias Köppe, Mauricio Collares

src/sage/interfaces/tachyon.py

@@ -683,12 +683,14 @@
 #*****************************************************************************
 
 import os
+import re
 
 from sage.cpython.string import bytes_to_str
 from sage.misc.pager import pager
 from sage.misc.superseded import deprecation
 from sage.misc.temporary_file import tmp_filename
 from sage.structure.sage_object import SageObject
+from sage.misc.cachefunc import cached_method
 
 
 class TachyonRT(SageObject):
@@ -799,6 +801,11 @@ def __call__(self, model, outfile='sage.png', verbose=1, extra_opts=''):
             Parser failed due to an input file syntax error.
             Aborting render.
         """
+        if self.version() >= '0.99.2':
+            # this keyword was changed in 0.99.2
+            model = model.replace(
+                    "              focallength ",
+                    "              focaldist ")
         modelfile = tmp_filename(ext='.dat')
         with open(modelfile, 'w') as file:
             file.write(model)
@@ -851,6 +858,25 @@ def usage(self, use_pager=True):
         else:
             print(r)
 
+    @cached_method
+    def version(self):
+        """
+        Returns the version of the Tachyon raytracer being used.
+
+        TESTS::
+
+            sage: tachyon_rt.version()  # random
+            0.98.9
+            sage: tachyon_rt.version() >= '0.98.9'
+            True
+        """
+        with os.popen('tachyon') as f:
+            r = f.readline()
+        res = re.search(r"Version ([\d.]*)", r)
+        # debian patches tachyon so it won't report the version
+        # we hardcode '0.99' since that's indeed the version they ship
+        return res[1] if res else '0.99'
+
     def help(self, use_pager=True):
         """
         Deprecated: type 'sage.interfaces.tachyon?' for help