users_guide: Convert mkUserGuidePart generation to a Sphinx extension

This removes all dependencies the users guide had on `mkUserGuidePart`.
The generation of the flag reference table and the various pieces of the
man page is now entirely contained within the Spinx extension
`flags.py`. You can see the man page generation on the orphan page
https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/ghc.html

The extension works by collecting all of the meta-data attached to the
`ghc-flag` directives and then formatting and displaying it at
`flag-print` directives. There is a single printing directive that can
be customized with two options, what format to display (table, list, or
block of flags) and an optional category to limit the output to
(verbosity, warnings, codegen, etc.).

New display formats can be added by creating a function
`generate_flag_xxx` (where `xxx` is a description of the format) which
takes a list of flags and a category and returns a new `xxx`. Then just
add a reference in the dispatch table `handlers`. That display can now
be run by passing `:type: xxx` to the `flag-print` directive.

`flags.py` contains two maps of settings that can be adjusted. The first
is a canonical list of flag categories, and the second sets default
categories for files.

The only functionality that Sphinx could not replace was the
`what_glasgow_exts_does.gen.rst` file. `mkUserGuidePart` actually just
reads the list of flags from `compiler/main/DynFlags.hs` which Sphinx
cannot do. As the flag is deprecated, I added the list as a static file
which can be updated manually.

Additionally, this patch updates every single documented flag with the
data from `mkUserGuidePart` to generate the reference table.

Fixes #11654 and, incidentally, #12155.

Reviewers: austin, bgamari

Subscribers: rwbarton, thomie

GHC Trac Issues: #11654, #12155

Differential Revision: https://phabricator.haskell.org/D3839

1 files changed, 23 insertions, 5 deletions

diff --git a/docs/users_guide/editing-guide.rst b/docs/users_guide/editing-guide.rst
index b57a5d12b9..ad49c8938c 100644
--- a/docs/users_guide/editing-guide.rst
+++ b/docs/users_guide/editing-guide.rst
@@ -347,11 +347,29 @@ Will be rendered as,
 
        Sets the context switch interval to ⟨s⟩ seconds.
 
-and will have an associated index entry generated automatically. Note that, as
-in Style Conventions below, we use ``⟨⟩`` instead of less-than/greater-than
-signs. To reference a ``ghc-flag`` or ``rts-flag``, you must match the
-definition exactly, including the arguments. A quick way to find the exact
-names and special characters is,
+and will have an associated index entry generated automatically.
+
+The ``ghc-flag`` directive requires a few extra parameters to be passed.
+This extra information is used to generate the :ref:`flag-reference` and the
+man page. A ``ghc-flag`` directive looks like this,
+
+.. code-block:: rest
+
+    .. ghc-flag:: -fasm
+        :shortdesc: Use the native code generator
+        :type: dynamic
+        :reverse: -fllvm
+        :category: codegen
+
+        Regular description...
+
+When rendered, the extra parameters will be hidden, and the data stored for
+later use. For more details, see the Sphinx extension ``flags.py``.
+
+Note that, as in Style Conventions below, we use ``⟨⟩`` instead of
+less-than/greater-than signs. To reference a ``ghc-flag`` or ``rts-flag``, you
+must match the definition exactly, including the arguments. A quick way to find
+the exact names and special characters is,
 
 .. code-block:: sh