Fix links to doc sources

Instead of figuring out a regex ourselves, just use `packaging` to
determine the version. And point to `master` branch if not on an actual
tag.

Fixes matplotlib#21230

Author: QuLogic

doc/conf.py

@@ -582,8 +582,8 @@ def setup(app):
 # You can add build old with link_github = False
 
 if link_github:
-    import re
     import inspect
+    from packaging.version import parse
 
     extensions.append('sphinx.ext.linkcode')
 
@@ -634,10 +634,9 @@ def linkcode_resolve(domain, info):
         if not fn.startswith(('matplotlib/', 'mpl_toolkits/')):
             return None
 
-        m = re.match(r'^.*post[0-9]+\+\w([a-z0-9]+).\w+$',
-                     matplotlib.__version__)
-        version = m.group(1) if m else f'v{matplotlib.__version__}'
+        version = parse(matplotlib.__version__)
+        tag = 'master' if version.is_devrelease else f'v{version.base_version}'
         return ("https://github.com/matplotlib/matplotlib/blob"
-                f"/{version}/lib/{fn}{linespec}")
+                f"/{tag}/lib/{fn}{linespec}")
 else:
     extensions.append('sphinx.ext.viewcode')

environment.yml

@@ -27,6 +27,7 @@ dependencies:
   - ipython
   - ipywidgets
   - numpydoc>=0.8
+  - packaging
   - pydata-sphinx-theme
   - scipy
   - sphinx>=1.8.1,!=2.0.0

requirements/doc/doc-requirements.txt

@@ -12,6 +12,7 @@ colorspacious
 ipython
 ipywidgets
 numpydoc>=0.8
+packaging>=20
 pydata-sphinx-theme>=0.6.0
 sphinxcontrib-svg2pdfconverter>=1.1.0
 # sphinx-gallery>=0.7