make doc-pdf fails

[Matthew Saltzman]

After some time, 'make doc-pdf' terminates with the following error messages. The key line is

[docpdf] ! Package babel Error: You haven't specified a language option.

The tail of the log is:

[docpdf] latexmk -pdf -dvi- -ps-  'references.tex'
[docpdf] Latexmk: This is Latexmk, John Collins, 18 June 2019, version: 4.65.
[docpdf] Rule 'pdflatex': The following rules & subrules became out-of-date:
[docpdf]       'pdflatex'
[docpdf] ------------
[docpdf] Run number 1 of rule 'pdflatex'
[docpdf] ------------
[docpdf] ------------
[docpdf] Running 'pdflatex   -recorder  "references.tex"'
[docpdf] ------------
[docpdf] Latexmk: applying rule 'pdflatex'...
[docpdf] This is pdfTeX, Version 3.14159265-2.6-1.40.19 (TeX Live 2018) (preloaded format=pdflatex)
[docpdf]  restricted \write18 enabled.
[docpdf] entering extended mode
[docpdf] (./references.tex
[docpdf] LaTeX2e <2017-04-15>
[docpdf] Babel <3.17> and hyphenation patterns for 3 language(s) loaded.
[docpdf] (./sphinxmanual.cls
[docpdf] Document Class: sphinxmanual 2018/12/22 v1.8.3 Document class (Sphinx manual)
[docpdf] (/usr/share/texlive/texmf-dist/tex/latex/base/report.cls
[docpdf] Document Class: report 2014/09/29 v1.4h Standard LaTeX document class
[docpdf] (/usr/share/texlive/texmf-dist/tex/latex/base/size10.clo)))
[docpdf] (/usr/share/texlive/texmf-dist/tex/latex/base/inputenc.sty
[docpdf] (/usr/share/texlive/texmf-dist/tex/latex/base/utf8.def
[docpdf] (/usr/share/texlive/texmf-dist/tex/latex/base/t1enc.dfu)
[docpdf] (/usr/share/texlive/texmf-dist/tex/latex/base/ot1enc.dfu)
[docpdf] (/usr/share/texlive/texmf-dist/tex/latex/base/omsenc.dfu)))
[docpdf] (/usr/share/texlive/texmf-dist/tex/latex/cmap/cmap.sty)
[docpdf] (/usr/share/texlive/texmf-dist/tex/latex/base/fontenc.sty
[docpdf] (/usr/share/texlive/texmf-dist/tex/latex/base/t1enc.def)<<t1.cmap>>)
[docpdf] (/usr/share/texlive/texmf-dist/tex/latex/amsmath/amsmath.sty
[docpdf] For additional information on amsmath, use the `?' option.
[docpdf] (/usr/share/texlive/texmf-dist/tex/latex/amsmath/amstext.sty
[docpdf] (/usr/share/texlive/texmf-dist/tex/latex/amsmath/amsgen.sty))
[docpdf] (/usr/share/texlive/texmf-dist/tex/latex/amsmath/amsbsy.sty)
[docpdf] (/usr/share/texlive/texmf-dist/tex/latex/amsmath/amsopn.sty))
[docpdf] (/usr/share/texlive/texmf-dist/tex/latex/amsfonts/amssymb.sty
[docpdf] (/usr/share/texlive/texmf-dist/tex/latex/amsfonts/amsfonts.sty))
[docpdf] (/usr/share/texlive/texmf-dist/tex/generic/babel/babel.sty
[docpdf] (/usr/share/texlive/texmf-dist/tex/generic/babel/switch.def)
[docpdf]
[docpdf] ! Package babel Error: You haven't specified a language option.
[docpdf]
[docpdf] See the babel package documentation for explanation.
[docpdf] Type  H <return>  for immediate help.
[docpdf]  ...                                             
[docpdf]                                                  
[docpdf] l.467 ...ry to proceed from here, type x to quit.}
[docpdf]                                                  
[docpdf] ?
[docpdf] ! Emergency stop.
[docpdf]  ...                                             
[docpdf]                                                  
[docpdf] l.467 ...ry to proceed from here, type x to quit.}
[docpdf]                                                  
[docpdf] !  ==> Fatal error occurred, no output PDF file produced!
[docpdf] Transcript written on references.log.
[docpdf] Collected error summary (may duplicate other messages):
[docpdf]   pdflatex: Command for 'pdflatex' gave return code 1
[docpdf]       Refer to 'references.log' for details
[docpdf] Latexmk: Use the -f option to force complete processing,
[docpdf]  unless error was exceeding maximum runs, or warnings treated as errors.
[docpdf] === TeX engine is 'pdfTeX'
[docpdf] Latexmk: Errors, so I did not complete making targets
[docpdf] make[2]: *** [Makefile:33: references.pdf] Error 12
[docpdf] make[2]: Leaving directory '/home/mjs/src/sage-9.0/local/share/doc/sage/latex/en/reference/references'
[docpdf] Error building the documentation.
[docpdf] Traceback (most recent call last):
[docpdf]   File "/home/mjs/src/sage-9.0/local/lib/python3.7/runpy.py", line 193, in _run_module_as_main
[docpdf]     "__main__", mod_spec)
[docpdf]   File "/home/mjs/src/sage-9.0/local/lib/python3.7/runpy.py", line 85, in _run_code
[docpdf]     exec(code, run_globals)
[docpdf]   File "/home/mjs/src/sage-9.0/local/lib/python3.7/site-packages/sage_setup/docbuild/__main__.py", line 2, in <module>
[docpdf]     main()
[docpdf]   File "/home/mjs/src/sage-9.0/local/lib/python3.7/site-packages/sage_setup/docbuild/__init__.py", line 1720, in main
[docpdf]     builder()
[docpdf]   File "/home/mjs/src/sage-9.0/local/lib/python3.7/site-packages/sage_setup/docbuild/__init__.py", line 332, in _wrapper
[docpdf]     getattr(get_builder(document), name)(*args, **kwds)
[docpdf]   File "/home/mjs/src/sage-9.0/local/lib/python3.7/site-packages/sage_setup/docbuild/__init__.py", line 550, in _wrapper
[docpdf]     self._build_bibliography(lang, format, *args, **kwds)
[docpdf]   File "/home/mjs/src/sage-9.0/local/lib/python3.7/site-packages/sage_setup/docbuild/__init__.py", line 527, in _build_bibliography
[docpdf]     build_many(build_ref_doc, references)
[docpdf]   File "/home/mjs/src/sage-9.0/local/lib/python3.7/site-packages/sage_setup/docbuild/__init__.py", line 280, in build_many
[docpdf]     _build_many(target, args, processes=NUM_THREADS)
[docpdf]   File "/home/mjs/src/sage-9.0/local/lib/python3.7/site-packages/sage_setup/docbuild/utils.py", line 283, in build_many
[docpdf]     raise worker_exc.original_exception
[docpdf] RuntimeError: failed to run $MAKE all-pdf in /home/mjs/src/sage-9.0/local/share/doc/sage/latex/en/reference/references
make[1]: *** [Makefile:2035: doc-pdf] Error 1
make[1]: Leaving directory '/home/mjs/src/sage-9.0/build/make'

real    4m37.627s
user    24m49.083s
sys    1m9.893s
***************************************************************
Error building Sage.

The following package(s) may have failed to build (not necessarily
during this run of 'make doc-pdf'):

* documentation: docpdf
  log file: /home/mjs/src/sage-9.0/logs/pkgs/../docpdf.log

The build directory may contain configuration files and other potentially
helpful information. WARNING: if you now run 'make' again, the build
directory will, by default, be deleted. Set the environment variable
SAGE_KEEP_BUILT_SPKGS to 'yes' to prevent this.