[PATCH] docs: pdfdocs: Adjust \headheight for fancyhdr

[Akira Yokosawa <akiyks@gmail.com>]

Fancyhdr prior to v4.0 outputs a message per document as follows:

    Package Fancyhdr Warning: \headheight is too small (12.0pt):
    Make it at least 13.59999pt.
    We now make it that large for the rest of the document.
    This may cause the page layout to be inconsistent, however.

Fancyhdr v4.0 complains (once a page!) as follows:

    Package fancyhdr Warning: \headheight is too small (12.0pt):
    (fancyhdr)    Make it at least 13.59999pt, for example:
    (fancyhdr)    \setlength{\headheight}{13.59999pt}.
    (fancyhdr)    You might also make \topmargin smaller to compensate:

    (fancyhdr)    \addtolength{\topmargin}{-1.59999pt}.

Related item in fancyhdr v4.0 announcement on 2021-01-04 [1]:

    Backward incompatible changes:
      - Eliminate adjustments of \headheight or \footskip, when the
        header or footer is too high.

[1]: https://www.ctan.org/ctan-ann/id/mailman.2685.1609863692.2532.ctan-ann@ctan.org

Silence the warnings by adding a couple of \addtolength commands in
the preamble.

Signed-off-by: Akira Yokosawa <akiyks@gmail.com>
---
Hi,

This update doesn't have much visual effects in the final PDFs
(adjustment of only 1.6pt), but getting rid of harmless warnings
would help spot potential important ones.

Tested against Sphinx versions 2.4.4 and 4.2.0, with Tex Live
versions 2017/debian (Ubuntu 18.04), 2019/debian (Ubuntu 20.04),
and vanilla 2021 (as of 2021-10-08).

        Thanks, Akira
--
 Documentation/conf.py | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/Documentation/conf.py b/Documentation/conf.py
index 948a97d6387d..17f7cee56987 100644
--- a/Documentation/conf.py
+++ b/Documentation/conf.py
@@ -353,6 +353,9 @@ latex_elements = {
         \\setsansfont{DejaVu Sans}
         \\setromanfont{DejaVu Serif}
         \\setmonofont{DejaVu Sans Mono}
+        % Adjust \\headheight for fancyhdr
+        \\addtolength{\\headheight}{1.6pt}
+        \\addtolength{\\topmargin}{-1.6pt}
      ''',
 }
 

base-commit: 7275423c177e5dcf53e350ab9db38f99946b8ec5
-- 
2.17.1