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Generated help messages and documentation
=========================================
This document assumes you've already read the corresponding sections in
:doc:`documenting`.
Command help
------------
.. _short_help_use:
How ``short_help`` gets used
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
All currently available commands are listed with their ``short_help`` string
when calling `help` without arguments, and is more or less the same as the
:ref:`command index <commandindex>`. The string is also used when hovering over
links to commands in the documentation, and in section headings like
:ref:`chformal autocmd`.
The next section shows the complete help text for the `chformal` command. This
can be displayed locally by using `help <command>` (or ``yosys -h <command>``
from the command line).
.. _chformal autocmd:
.. autocmd:: chformal
:noindex:
.. _warning_flages_use:
What do warning flags do
~~~~~~~~~~~~~~~~~~~~~~~~
Calling commands with the ``experimental`` flag set, will also call
``log_experimental()`` with the name of the pass, providing an additional
warning any time the pass is used. Commands with the ``internal`` flag set will
be included in :doc:`/cmd/index_internal`, overriding any other command group
they may have been assigned. In both cases, commands with these flags set will
print additional warning text in the help output.
.. note::
When testing the handling of expected error/warning messages with e.g.
`logger`, it is possible to disable the warnings for a given experimental
feature. This can be done by calling Yosys with ``--experimental
<feature>``, where ``<feature>`` is the name of the experimental pass.
.. _pass_help:
The ``Pass::help()`` method
~~~~~~~~~~~~~~~~~~~~~~~~~~~
.. TODO::
We should talk here about how the ``formatted_help`` is a formalization of
how ``help()`` was expected to be used, and how this method should only be
overridden if ``formatted_help()`` returns false (or is not overridden).
.. TODO:: reverse the framing in the following paragraph
since this is now (effectively) after ``formatted_help()``
The second purpose of ``Pass::formatted_help`` is to provide richer help
content which is able to take advantage of the reStructuredText formatting used
here in the web docs. It also provides a more fluid way of writing help text,
without getting caught up in the terminal-first spacing requirements of writing
for ``Pass::help()``.
Overriding this method is the original way to provide help text, and as of this
writing is still the most common. The ``log()`` function should be called
directly to print and format the help text, and each line should be limited to
80 (printed) characters. While it is possible to provide arbitrary formatting,
it is preferred to follow the guidelines here to maintain consistency with other
passes and to assist in correct parsing and formatting during RST generation
(i.e. these docs).
.. note::
It is good practice in the ``Pass::help`` method for each call to ``log()`` to
correspond to a single line, containing exactly one ``\n`` (at the end). This
allows the appearance in source to match the appearance in the terminal.
The first and last lines should always be empty, followed by the primary usage
signature for the command. Each usage signature should be indented with 4
spaces, and followed by an empty line. Each option or flag should start on a
new line indented with 4 spaces, followed by a description of the option which
is indented by a further 4 spaces, and then an empty line. Where multiple
options share a description the empty line between options should be omitted.
.. note::
`Commands JSON`_ has more on how formatting in ``help()`` gets parsed.
The ``Pass::formatted_help()`` method
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.. TODO:: discuss ``PrettyHelp::get_current()`` over a function arg
and remove redundant info
The ``formatted_help`` method serves two purposes in help generation, both of
which are optional. In both cases, any pass which uses the method should
``#include "kernel/log_help.h"``, and begin the method by calling ``auto *help =
PrettyHelp::get_current();``. The method finishes by returning a boolean value.
``true`` means help content has been added to the current ``PrettyHelp``, while
``false`` indicates that ``Pass::help()`` should be called instead.
Setting a command group
^^^^^^^^^^^^^^^^^^^^^^^
.. TODO:: move this into other headings
- used when `dumping to JSON`_
- e.g. ``autocmdgroup`` directive in :file:`docs/source/cmd/index_formal.rst`
for all the ``formal`` commands
- Because ``Pass::formatted_help()`` returns if it produced help content, it is
completely valid to override the method, get the current instance of
``PrettyHelp``, set the command group, and then return ``false``.
.. warning::
There is currently no warning available for groups that do not have a
corresponding ``autocmdgroup``. If you add a new command group, make sure
that it has a corresponding index page.
Command line rendering
~~~~~~~~~~~~~~~~~~~~~~
Rendering text for the command line is done by the ``Pass::help`` method. When
this method is not overridden, the default behavior is to call
``Pass::formatted_help()``. If this method is also left unimplemented, or the
return value is explicitly false, then a default message about missing help text
for the command is displayed. Returning true, however, will then call
``PrettyHelp::log_help()`` to convert the formatted help content into plain
text.
.. note::
Regardless of which help method is used, any `what do warning flags do`_ set
on the pass will display a message to warn the user. These are regular
messages, using ``log()`` rather than ``log_warning()``, meaning (for
example) they will be suppressed by the ``-q`` command line option.
Rendering rich help text as plain text is done by traversing over all the
``ContentListing`` nodes and printing the body text. ``usage`` nodes are
preceded by an empty line and indented one level (4 spaces). ``option`` nodes
are also indented one level, while their children are indented an extra level (8
spaces). Any ``codeblock`` nodes are rendered as-is at the current indentation,
with no further formatting applied.
``paragraph`` nodes are broken into words separated by spaces, and each word is
printed. If a word would cause the current line to exceed 80 characters
(controlled by ``MAX_LINE_LEN`` in :file:`kernel/log_help.cc`), then the word
will instead be placed on a new line with the same level of indentation. Special
handling is included for words that begin and end with a backtick (`````) so
that these are stripped when printing to the command line. Compare
:ref:`chformal_help` below with the :ref:`chformal autocmd` above. The content
is still the same, but for the command line it uses a fixed width.
Cell help
---------
Calling `help -cells` will list all built-in cell types with their input/output
ports. There is again an unlisted :ref:`cell index <cellindex>` which shows all
cell types with their title. Unlike commands, providing a title is optional,
and only available with `v2`_ formatting, so most just use the name of the cell
(qualified with the containing group). It is also possible to display the
verilog simulation model by calling `help <celltype>+`.
Each verilog module (and its comment block) is parsed into a C++ ``dict``,
mapping the cell type (the name of the verilog module) to a ``SimHelper``
struct in :file:`kernel/register.cc` with ``#include``\ s. Calling `help
<celltype>` then retrieves the corresponding ``SimHelper`` and displays the
help text contained.
.. _v1:
v1 (default)
~~~~~~~~~~~~
.. TODO:: fixup, limitations
The description is rendered to the terminal as-is when calling `help
<celltype>`, while the web docs will render it as text, with empty lines being
used to separate paragraphs.
.. note::
Most of the legacy cell descriptions include a signature line (``//-
$<celltype> (<ports>)``). More recent versions of the help generation will
automatically produce this signature from the verilog declaration, making
this an optional inclusion. Note that if a signature line *is* included, it
*must* start with at least 4 spaces (not tabs), and include one empty line
(``//-``) before and after.
Each cell type must also be assigned a group, failing to do so will produce an
error. This can be done by adding ``//* group <cellgroup>`` anywhere in the
comment block. As with commands, the group determines where the cell appears in
the Sphinx documentation, but does not otherwise impact the output of `help`. As
with commands, there is no warning produced if cells are assigned a group which
is not used in the documentation. Make sure to check :file:`docs/source/cell`
for the groups currently available.
For the cell models in :file:`techlibs/common/simcells.v`, it is possible to
provide a truth table at the end of the cell description which is rendered in
sphinx docs as a literal code block. We can look at the :ref:`NOT_module` to
see this in action.
.. literalinclude:: /generated/simcells._NOT_.v
:language: verilog
:start-at: //-
:end-at: module \$_NOT_
:name: NOT_module
:caption: `$_NOT_` cell comment block from :file:`techlibs/common/simcells.v`
..
v1 descriptions in :file:`techlibs/common/simcells.v` have their version
unconditionally changed to ``2a`` to facilitate the truth table rendering,
making use of the v2 handling of codeblocks with ``::``. This also means A.
using ``::`` on its own in a v1 (gate-level) description should be avoided, and
B. *all* text after the ``"Truth table:"`` line is included in the codeblock.
.. _v2:
v2 (more expressive)
~~~~~~~~~~~~~~~~~~~~
.. TODO:: fixup
When generating the Sphinx documentation, the cell description is interpreted as
raw RST. This allows both in-line formatting like linking to commands or passes
using backticks (`````)
.. todo:: in line formatting for web docs isn't exclusive to v2,
but it does raise the question of if we should be doing something to prevent
v1 descriptions being treated as raw RST.
Dumping to JSON
---------------
Once compiled, Yosys is able to dump both the internal command and cell
libraries to a machine-readable JSON file. Primarily intended for building this
documentation (more on that in the next section), this feature is not advertised
within Yosys itself, and can be done with `help -dump-cmds-json <cmds.json>` and
`help -dump-cells-json <cells.json>` respectively.
Both JSON files are formatted very similarly, containing a single object. The
object has a ``version`` field which disambiguates between the two, a
``generator`` field which contains the Yosys version string used, a ``groups``
object which maps each group to the list of commands/cells in that group, and
finally a ``cmds`` or ``cells`` object which maps each command/cell to its help
content.
.. TODO:: Document how things get to Read the Docs
- :file:`.github/workflows/prepare-docs.yml`
- github job compiles Yosys (with Verific)
- dumps JSON
- dumps program usage output for :doc:`/cmd_ref` and
:doc:`/appendix/auxprogs`
- runs examples, producing logs and images
- copies (some) source files for inclusion
- compresses and uploads artifact
- conditionally triggers RTDs to build
- ``rtds_action`` extension
Commands JSON
~~~~~~~~~~~~~
Lets take a look at :ref:`chformal_json` as an example. We can see the bulk of
the object is taken up by the ``content`` field, which contains all the
``ContentListing`` nodes we added in :ref:`the formatted_help method for
chformal <chformal_source>`, maintaining the structure of those nodes. The
command's ``short_help`` is given in the ``title`` field, with other fields for
the `what do warning flags do`_, source location, source function, and
corresponding group (either implicit or explicit).
.. literalinclude:: /generated/cmds.json
:language: json
:start-at: "chformal": {
:end-at: "internal_flag": false
:append: }
:dedent:
:caption: `chformal` in generated :file:`cmds.json`
:name: chformal_json
Every command registered in Yosys (including those from currently installed
plugins) has a corresponding object in the JSON dump. For commands where
``Pass::formatted_help()`` is unimplemented or returns false, ``ContentListing``
nodes will be generated by parsing the unformatted ``Pass::help()`` output. This
is largely the same as `Command line rendering`_ but in reverse, with a few
simple rules to try convert between raw text and the different node types.
To be parsed as a ``usage`` node, the current line:
+ must start with the name of the command (case sensitive), followed by a
space or a new line;
+ may have up to four characters of whitespace as indentation;
+ must be the first non-empty line, preceded by two empty lines, or
immediately following another usage signature with the same indentation.
Any lines immediately after a usage signature which is indented more than the
signature will be appended to the usage signature. This allows for breaking
arguments across lines in the terminal output while still producing a single
``usage`` node.
.. code-block:: cpp
:caption: Example code for a command with multiple usage signatures
log("\n");
log(" command\n");
log(" command -argument\n");
log(" -another argument\n");
log("\n");
log("\n");
log("command description.\n"); // not a signature because it is dedented
log("\n");
log("\n");
log(" command -different argument\n");
log("\n");
If a line is indented and starts with a dash (``-``), and does not immediately
follow a usage signature, it is parsed as an ``option`` node. Anything else is
parsed as a ``codeblock`` and added to either the root node or the current
option depending on the indentation. This allows yosys script syntax
highlighting for (most) options, while still respecting help content which
relies on the fixed-width rendering.
To enable syntax highlighting in synthesis command scripts, if the final block
of help output starts with the string ``"The following commands are executed by
this synthesis command:\n"``, then the rest of the code block is formatted as
``yoscrypt`` (e.g. `synth_ice40`). The caveat here is that if the ``script()``
calls ``run()`` on any commands *prior* to the first ``check_label`` then the
auto detection will break and revert to unformatted code (e.g.
`synth_fabulous`).
Cells JSON
~~~~~~~~~~
Dumping the cell help contents to JSON follows a very similar format as the
``SimHelper`` struct. The main difference is that there is no ``ver`` or
``group`` field, and the ``tags`` have become ``properties``. Each cell type
also has a corresponding ``CellType`` struct defined in
:file:`kernel/celltypes.h` which we now have access to. This allows us to
distinguish which ports are inputs and which are outputs, as well as some extra
property flags. The :ref:`nex_json` is reproduced here to show this
transformation.
.. literalinclude:: /generated/cells.json
:language: json
:start-at: "$nex": {
:end-at: },
:caption: `$nex` in generated :file:`cells.json`
:name: nex_json
Working with Sphinx
-------------------
This documentation is built on Sphinx using `reStructuredText`_. To support the
rich documentation of commands and cells in Yosys, as well as the Yosys
scripting language and RTLIL, we use some custom extensions and will touch on
those here.
.. _reStructuredText: https://docutils.sourceforge.io/rst.html
Sphinx uses `Pygments`_ for syntax highlighting code blocks, for which we
provide to additional lexers. The first of these is ``RTLIL`` for the
:doc:`/yosys_internals/formats/rtlil_rep`, and is exclusive to the Yosys docs.
The second lexer, ``yoscrypt``, is for :doc:`/getting_started/scripting_intro`
and is available across all of the YosysHQ docs through `furo-ys`_, our custom
fork of the `furo`_ theme for Sphinx. These languages are automatically
associated with the ``.il`` and ``.ys`` file extensions respectively, and can be
selected for use in any ``literalinclude`` or ``code-block`` segments.
.. _Pygments: https://pygments.org/
.. _furo-ys: https://github.com/YosysHQ/furo-ys/
.. _furo: https://github.com/pradyunsg/furo
To simplify inline Yosys script syntax highlighting, these docs provide the
``yoscrypt`` role. This role renders (e.g.) ``:yoscrypt:`chformal -remove```
into :yoscrypt:`chformal -remove`. For linking to command and cell
documentation, we also use a default role of ``autoref``. Any text in single
backticks without an explicit role will be assigned this one. We've already
seen this being used above in the help text for `chformal` and `$nex` (which
were themselves written as ```chformal``` and ```$nex``` respectively).
By using the `autodoc extension`_ and two custom `Sphinx Domains`_ (more on them
later), ``autoref`` is able to produce links to any commands or cells available
in Yosys. So long as there are no spaces in the text, and it doesn't begin with
a dash (``-``), it will try to convert it to a link. If the text begins with
``$`` then it will use the ``cell:ref`` role, otherwise it will use ``cmd:ref``.
Let's take a look at some examples:
.. _Sphinx Domains: https://www.sphinx-doc.org/en/master/usage/domains/index.html
.. _autodoc extension: https://www.sphinx-doc.org/en/master/usage/extensions/autodoc.html
.. tab:: reStructuredText
.. literalinclude:: formatting_sample.txt
:language: reStructuredText
:start-after: .. 1
:end-before: .. 2
.. tab:: formatted output
.. include:: formatting_sample.txt
:start-after: .. 1
:end-before: .. 2
Notice how referencing `chformal` also puts the command name in an inline code
block. This is automatically done thanks to the use of `Sphinx Domains`_ and
helps to distinguish commands (and cells) from other types of links. The
``autoref`` role also works with two words, if the first one is "help":
.. tab:: reStructuredText
.. literalinclude:: formatting_sample.txt
:language: reStructuredText
:start-after: .. 2
:end-before: .. 3
.. tab:: formatted output
.. include:: formatting_sample.txt
:start-after: .. 2
:end-before: .. 3
And if the text begins with a dash, or doesn't match the "help" formatting, it
will fallback to formatting as inline yoscrypt.
.. tab:: reStructuredText
.. literalinclude:: formatting_sample.txt
:language: reStructuredText
:start-after: .. 3
:end-before: .. 4
.. tab:: formatted output
.. include:: formatting_sample.txt
:start-after: .. 3
:end-before: .. 4
Using autodoc
~~~~~~~~~~~~~
The vast majority of command and cell help content in these docs is done with
the the `autodoc extension`_. By generating Sphinx documentation from our JSON
dumps of commands and cells, not only are we able to write the help content once
and have it available both in Yosys itself and online, we also ensure that any
code changes or additions are automatically propagated to the web docs.
.. note::
We are focusing on the ``autocmd`` directive here because it is easier to
demonstrate. In practice we don't really use it directly outside of this
page, and instead make use of the ``autocmdgroup`` directive. By providing
the ``:members:`` option, this is the same as calling ``autocmd`` for each
command in the group and means that any new commands are added automatically.
Now let's take a look at the :ref:`chformal_rst` behind :ref:`chformal autocmd`.
This conversion is done by the ``YosysCmdDocumenter`` class in
:file:`docs/util/cmd_documenter.py`. We can see all of our ``paragraph`` and
``option`` nodes from :ref:`ChformalPass::formatted_help() <chformal_source>`
have made it through, as has the ``short_help`` from our :ref:`ChformalPass()
constructor <chformal_pass>`. The heading will be rendered as a subheading of
the most recent heading (notice how the `chformal` help content above is listed
under `Command help`_ in the table of contents).
.. _chformal_rst:
.. autocmd_rst:: chformal
To support cross references with the ``cmd:ref`` role, we see everything is
under the ``cmd:def`` directive. The ``:title:`` option is what controls the
text that appears when hovering over the `chformal` link, and when using the
``cmd:title`` role. For commands with `what do warning flags do`_, a ``..
warning`` block is added to the generated RST before any of the help content.
This is the same `warning admonition`_ that we've seen elsewhere on this page.
For commands with no ``source_location``, the ``.. seealso`` block at the bottom
will instead link to :doc:`/cmd/index_other`.
.. _warning admonition: https://pradyunsg.me/furo/reference/admonitions/#warning
.. hint::
The :ref:`chformal autocmd` on this page uses the ``:noindex:`` option so
that references to `chformal` link to the :doc:`/cmd_ref` instead of this
page.
For documenting cells we have ``autocell`` and ``autocellgroup``, which function
pretty similarly to their command-based counter parts, ``autocmd`` and
``autocmdgroup``. These directives are provided by the ``YosysCellDocumenter``
in :file:`docs/util/cell_documenter.py`. Like with `help <celltype>+`, we are
able to include verilog simulation models in our ``autodoc`` with the
``:source:`` option. We can then also include line numbers by adding
``:linenos:``, which is very useful when trying to find the source code being
referenced.
.. todo:: would be nice to get a ``.. autocell:: $nex``
like we did with `chformal autocmd`_, but it doesn't seem to like the
``:noindex:`` option, or using ``:source:`` without it being
``binary::$nex``.
.. todo:: cells can have properties (:ref:`propindex`)
.. note::
For :ref:`showing autocmd generated rst <chformal_rst>` on this page, we also
have the ``autocmd_rst`` directive. This is not used anywhere else in the
documentation, but it's mentioned here since we're already deep in the weeds
of how these docs are made.
Our custom Sphinx domains
~~~~~~~~~~~~~~~~~~~~~~~~~
To round out this document about documentation, let's take a brief look at our
custom Sphinx domains and what they provide. As you might expect from `Using
autodoc`_, these docs come with a domain for Yosys commands (``cmd``), and a
domain for built-in cells (``cell``). These are both provided in
:file:`docs/util/custom_directives.py`. From these domains we have the
following directives (``.. <directive>::`` in RST):
- ``cmd:def`` provide command definition,
- ``cmd:usage`` used by ``autocmd`` for command usage signatures,
- ``cell:def`` provide cell definition,
- ``cell:defprop`` provide cell property definition (used in
:doc:`/cell/properties`), and
- ``cell:source`` used by ``autocell`` for simulation models.
For general documentation, it should not be necessary to interact with any of
these directives. Rather, everything should be accomplished through the use of
``autocmdgroup`` and ``autocellgroup``. We also have a few roles provided
(``:<role>:`<command or cell>``` in RST):
- ``cmd:ref`` link to a ``cmd:def`` with the same name
- ``cmd:title`` same as ``cmd:ref``, but includes the short help in the text
- ``cell:ref`` link to a ``cell:def`` with the same name
- ``cell:title`` same as ``cell:ref``, but includes the title in the text
- ``cell:prop`` link to a ``cell:defprop`` of the same name
For the ``<domain>:ref`` roles it's almost always easier to just not specify the
role; that's why ``autoref`` is there. And since all of the built-in cell types
start with ``$``, it's very easy to distinguish between a ``cmd:ref`` and a
``cell:ref``. When introducing a command it can be useful to quickly insert a
short description of it, so ``cmd:title`` sees a fair bit of use across the
documentation; particularly when it comes to the user-facing sections:
.. TODO:: is this the first time we mention the user/developer split?
.. tab:: reStructuredText
.. literalinclude:: formatting_sample.txt
:language: reStructuredText
:start-after: .. 4
:end-before: .. 5
.. tab:: formatted output
.. include:: formatting_sample.txt
:start-after: .. 4
:end-before: .. 5
Since only a small subset of cells provide titles (at the time of writing),
``cell:title`` is much less reliable, and more likely to give something that
isn't intended for the reader to see (like with `$_NOT_` in the above example).
The existence of ``cell:title`` is mostly an artifact of the ``CellDomain``
being a subclass of the ``CommandDomain``.
.. warning::
Because of how Sphinx caches domains (and/or because of how the
``CommandDomain`` is setup), rebuilding pages with ``autocmdgroup`` or
``autocellgroup`` directives can result in duplicate definitions on the
:ref:`command <commandindex>` and :ref:`cell <cellindex>` indices. A ``make
clean`` or ``rm -rf docs/build`` will resolve this. The online documentation
is not affected by this, since it always performs a clean build.
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