DOC: Skip creating redirects if docs build fails

[datapythonista]

When the doc build fails, we still try to create the redirected pages, which fails, and adds to the log a misleading error (it looks in the logs like the problem is not the original error but that something is failing in the redirects).

See for example https://travis-ci.org/pandas-dev/pandas/jobs/542714631:

Recursion error:
maximum recursion depth exceeded while calling a Python object
This can happen with very large or deeply nested source files.  You can carefully increase the default Python recursion limit of 1000 in conf.py with e.g.:
    import sys; sys.setrecursionlimit(1500)
Traceback (most recent call last):
  File "./make.py", line 341, in <module>
    sys.exit(main())
  File "./make.py", line 337, in main
    return getattr(builder, args.command)()
  File "./make.py", line 226, in html
    self._add_redirects()
  File "./make.py", line 209, in _add_redirects
    with open(path, 'w') as moved_page_fd:
FileNotFoundError: [Errno 2] No such file or directory: '/home/travis/build/pandas-dev/pandas/doc/build/html/generated/pandas.api.extensions.ExtensionArray.argsort.html'

Here I make the redirects be created only if the doc build succeeded. Also opening the browser if we're building a single page.

[codecov]

Codecov Report

Merging #26752 into master will decrease coverage by 1.41%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #26752      +/-   ##
==========================================
- Coverage    91.7%   90.29%   -1.42%     
==========================================
  Files         179      179              
  Lines       50767    50767              
==========================================
- Hits        46555    45839     -716     
- Misses       4212     4928     +716

Flag	Coverage Δ
#multiple	90.29% <ø> (ø)	⬆️
#single	?

Impacted Files	Coverage Δ
pandas/core/computation/pytables.py	62.5% <0%> (-27.75%)	⬇️
pandas/io/pytables.py	63.82% <0%> (-26.48%)	⬇️
pandas/io/gbq.py	78.94% <0%> (-10.53%)	⬇️
pandas/core/computation/common.py	84.21% <0%> (-5.27%)	⬇️
pandas/core/computation/expr.py	94.5% <0%> (-3.03%)	⬇️
pandas/io/clipboard/clipboards.py	31.88% <0%> (-2.9%)	⬇️
pandas/io/formats/printing.py	84.49% <0%> (-1.07%)	⬇️
pandas/core/indexes/datetimes.py	96.21% <0%> (-0.17%)	⬇️
pandas/core/arrays/categorical.py	95.8% <0%> (-0.13%)	⬇️
pandas/core/frame.py	96.88% <0%> (-0.12%)	⬇️

---

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Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
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[codecov]

Codecov Report

Merging #26752 into master will decrease coverage by 1.41%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #26752      +/-   ##
==========================================
- Coverage    91.7%   90.29%   -1.42%     
==========================================
  Files         179      179              
  Lines       50767    50767              
==========================================
- Hits        46555    45839     -716     
- Misses       4212     4928     +716

Flag	Coverage Δ
#multiple	90.29% <ø> (ø)	⬆️
#single	?

Impacted Files	Coverage Δ
pandas/core/computation/pytables.py	62.5% <0%> (-27.75%)	⬇️
pandas/io/pytables.py	63.82% <0%> (-26.48%)	⬇️
pandas/io/gbq.py	78.94% <0%> (-10.53%)	⬇️
pandas/core/computation/common.py	84.21% <0%> (-5.27%)	⬇️
pandas/core/computation/expr.py	94.5% <0%> (-3.03%)	⬇️
pandas/io/clipboard/clipboards.py	31.88% <0%> (-2.9%)	⬇️
pandas/io/formats/printing.py	84.49% <0%> (-1.07%)	⬇️
pandas/core/indexes/datetimes.py	96.21% <0%> (-0.17%)	⬇️
pandas/core/arrays/categorical.py	95.8% <0%> (-0.13%)	⬇️
pandas/core/frame.py	96.88% <0%> (-0.12%)	⬇️

---

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Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update c7748ca...ab4af39. Read the comment docs.

[WillAyd]

Did this error just pop up with a new version of sphinx?

[datapythonista]

Yep, the error was fixed in #26727. This PR is just for future failures of the doc build, to not include the misleading redirects error.

[jreback]

do we already have a good error message to the user if the build fails?

[datapythonista]

yes, we'll have the sphinx error message. In the example in the description, the end of the log will be:

Recursion error:
maximum recursion depth exceeded while calling a Python object
This can happen with very large or deeply nested source files.  You can carefully increase the default Python recursion limit of 1000 in conf.py with e.g.:
    import sys; sys.setrecursionlimit(1500)

[jreback]

thanks @datapythonista