[PATCH v2 2/3] docs/conf.py: Respect env variable SPHINX_IMGMATH

[Akira Yokosawa <akiyks@gmail.com>]

On some distros with coarse-grained packaging policy, dvipng is
installed along with latex.  In such cases, math rendering will
use imgmath by default.  It is possible to override the choice by
specifying the option string of "-D html_math_renderer='mathjax'"
to sphinx-build (Sphinx >= 1.8).

To provide developers an easier-to-use knob, add code for an env
variable "SPHINX_IMGMATH" which overrides the automatic choice
of math renderer for html docs.

    SPHINX_IMGMATH=yes : Load imgmath even if dvipng is not found
    SPHINX_IMGMATH=no  : Don't load imgmath (fall back to mathjax)

Signed-off-by: Akira Yokosawa <akiyks@gmail.com>
Acked-by: Mauro Carvalho Chehab <mchehab@kernel.org>
---
Changes since v1:
 - No logical changes.
 - Renames:
     LOAD_IMGMATH -> SPHINX_IMGMATH (Mauro),
     opt_load_imgmath -> env_sphinx_imgmath.
 - Acked-by from Mauro.

--
 Documentation/conf.py | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/Documentation/conf.py b/Documentation/conf.py
index 3ec1f845c839..0b8f20e8e22c 100644
--- a/Documentation/conf.py
+++ b/Documentation/conf.py
@@ -128,8 +128,20 @@ autosectionlabel_maxdepth = 2
 # mathjax is the default math renderer since Sphinx 1.8.
 have_latex =  have_command('latex', '--version', 'pdfTeX')
 have_dvipng = have_command('dvipng', '--version', 'dvipng')
-load_imgmath = ((have_latex and have_dvipng)
-                or (major == 1 and minor < 8)
+load_imgmath = have_latex and have_dvipng
+
+# Respect SPHINX_IMGMATH (for html docs only)
+if 'SPHINX_IMGMATH' in os.environ:
+    env_sphinx_imgmath = os.environ['SPHINX_IMGMATH']
+    if 'yes' in env_sphinx_imgmath:
+        load_imgmath = True
+    elif 'no' in env_sphinx_imgmath:
+        load_imgmath = False
+    else: # otherwide, auto selection
+        pass
+
+# Always load imgmath for Sphinx <1.8 or for epub docs
+load_imgmath = (load_imgmath or (major == 1 and minor < 8)
                 or 'epub' in sys.argv)
 
 if load_imgmath:
-- 
2.25.1