This patch is taken from upstream.  It fixes documentation generation.
The patch has been lightly adapted to apply to the release tarball, but
the commit message was left untouched, so it refers to some changes not
included in the patch.

From 0d9a81e20238a6b72f9f5c005f1f7e9cf05f6fb9 Mon Sep 17 00:00:00 2001
From: Alec Theriault <alec.theriault@gmail.com>
Date: Sat, 27 Oct 2018 10:05:04 -0700
Subject: [PATCH] Fix documentation in `haddock-api` (#957)

* Fix misplaced Haddocks in Haddock itself

Haddock should be able to generate documentation for 'haddock-api'
again.

* Make CI check that documentation can be built.

* Add back a doc that is OK
---
 .travis.yml                               |  3 +++
 haddock-api/src/Haddock/Backends/LaTeX.hs | 10 +++++-----
 2 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/src/Haddock/Backends/LaTeX.hs b/src/Haddock/Backends/LaTeX.hs
index 4e0e6eba..613c6deb 100644
--- a/src/Haddock/Backends/LaTeX.hs
+++ b/src/Haddock/Backends/LaTeX.hs
@@ -243,8 +243,8 @@ ppDocGroup lev doc = sec lev <> braces doc
 
 -- | Given a declaration, extract out the names being declared
 declNames :: LHsDecl DocNameI
-          -> ( LaTeX           -- ^ to print before each name in an export list
-             , [DocName]       -- ^ names being declared
+          -> ( LaTeX           --   to print before each name in an export list
+             , [DocName]       --   names being declared
              )
 declNames (L _ decl) = case decl of
   TyClD _ d  -> (empty, [tcdName d])
@@ -444,9 +444,9 @@ ppLPatSig doc docnames ty unicode
 -- arguments as needed.
 ppTypeOrFunSig :: HsType DocNameI
                -> DocForDecl DocName  -- ^ documentation
-               -> ( LaTeX             -- ^ first-line (no-argument docs only)
-                  , LaTeX             -- ^ first-line (argument docs only)
-                  , LaTeX             -- ^ type prefix (argument docs only)
+               -> ( LaTeX             --   first-line (no-argument docs only)
+                  , LaTeX             --   first-line (argument docs only)
+                  , LaTeX             --   type prefix (argument docs only)
                   )
                -> Bool                -- ^ unicode
                -> LaTeX
-- 
2.23.0

><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/tests/substitute.scm?id=019c862a67b677ceeb0d91c9440f5ed8d9c149a4&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2021-04-09 17:46:38 +0200'>2021-04-09</span></td><td><a href='/guix/commit/tests/substitute.scm?id=2d73086262e1fb33cd0f0f16f74a495fe06b38aa'>daemon: 'guix substitute' replies on FD 4.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2021-01-16 11:51:03 +0000'>2021-01-16</span></td><td><a href='/guix/commit/tests/substitute.scm?id=681af17460fa34916ac40589cccdcca7222249af'>guix: Move narinfo code from substitute script to module.</a><span class='msg-avail'>...</span></td><td>Christopher Baines</td></tr>
s in lieu of &lt;package&gt;s.</a><span class='msg-avail'>...</span></td><td>Tobias Geerinckx-Rice</td></tr>