Set fail_on_warning to true in RTD config

[parulin]

Since nitpicky mode is enabled and all warnings are fixed, using this default may spot minor mistakes in pull requests.

[marmarek]

It fails to build now...

writing content.opf file...
WARNING: unknown mimetype for _static/admin-api-architecture.dia, ignoring [epub.unknown_project_files]
WARNING: unknown mimetype for _static/arch-spec-0.3.pdf, ignoring [epub.unknown_project_files]
Writing evaluated template result to /home/docs/checkouts/readthedocs.org/user_builds/qubes-doc/checkouts/latest/_readthedocs/epub/content.opf
writing nav.xhtml file...
Writing evaluated template result to /home/docs/checkouts/readthedocs.org/user_builds/qubes-doc/checkouts/latest/_readthedocs/epub/nav.xhtml
writing toc.ncx file...
Writing evaluated template result to /home/docs/checkouts/readthedocs.org/user_builds/qubes-doc/checkouts/latest/_readthedocs/epub/toc.ncx
writing QubesOS.epub file...
build finished with problems, 2 warnings (with warnings treated as errors).

[rapenne-s]

It fails to build now...

writing content.opf file...
WARNING: unknown mimetype for _static/admin-api-architecture.dia, ignoring [epub.unknown_project_files]
WARNING: unknown mimetype for _static/arch-spec-0.3.pdf, ignoring [epub.unknown_project_files]
Writing evaluated template result to /home/docs/checkouts/readthedocs.org/user_builds/qubes-doc/checkouts/latest/_readthedocs/epub/content.opf
writing nav.xhtml file...
Writing evaluated template result to /home/docs/checkouts/readthedocs.org/user_builds/qubes-doc/checkouts/latest/_readthedocs/epub/nav.xhtml
writing toc.ncx file...
Writing evaluated template result to /home/docs/checkouts/readthedocs.org/user_builds/qubes-doc/checkouts/latest/_readthedocs/epub/toc.ncx
writing QubesOS.epub file...
build finished with problems, 2 warnings (with warnings treated as errors).

Thanks for reporting this, this is unfortunate and unexpected. I'm trying with sphinx-build -b html locally and it works fine, it seems not sufficient to compare to what rtd is running to build the doc.

I'll revert this commit.

[parulin]

It seems to be related to the epub version...

[parulin]

I found a workaround but anyway, I think it might be better to think a bit more about this...

With builds from pull requests, only HTML formats are generated. Other formats are resource intensive and will be built after merging.

That means that there is currently no way to check the full build process before merging?

Related: readthedocs/readthedocs.org#9816