fish-shell/doc_src/cmds/string-length.rst
Johannes Altmanninger c0d1e41313 docs synopsis: add HTML highlighing and automate manpage markup
Recent synopsis changes move from literal code blocks to
[RST line blocks].  This does not translate well to HTML: it's not
rendered in monospace, so aligment is lost.  Additionally, we don't
get syntax highlighting in HTML, which adds differences to our code
samples which are highlighted.

We hard-wrap synopsis lines (like code blocks). To align continuation
lines in manpages we need [backslashes in weird places]. Combined with
the **, *, and `` markup, it's a bit hard to get the alignment right.

Fix these by moving synopsis sources back to code blocks and compute
HTML syntax highlighting and manpage markup with a custom Sphinx
extension.

The new Pygments lexer can tokenize a synopsis and assign the various
highlighting roles, which closely matches fish's syntax highlighing:
- command/keyword (dark blue)
- parameter (light blue)
- operator like and/or/not/&&/|| (cyan)
- grammar metacharacter (black)

For manpage output, we don't project the fish syntax highlighting
but follow the markup convention in GNU's man(1):

	bold text          type exactly as shown.
	italic text        replace with appropriate argument.

To make it easy to separate these two automatically, formalize that
(italic) placeholders must be uppercase; while all lowercase text is
interpreted literally (so rendered bold).
This makes manpages more consistent, see string-join(1) and and(1).

Implementation notes:
Since we want manpage formatting but Sphinx's Pygments highlighing
plugin does not support manpage output, add our custom "synopsis"
directive.  This directive parses differently when manpage output is
specified. This means that the HTML and manpage build processes must
not share a cache, because the parsed doctrees are cached.  Work around
this by using separate cache locations for build targets "sphinx-docs"
(which creates HTML) and "sphinx-manpages".  A better solution would
be to only override Sphinx's ManualPageBuilder but that would take a
bit more code (ideally we could override ManualPageWriter but Sphinx
4.3.2 doesn't really support that).

---

Alternative solution: stick with line blocks but use roles like
:command: or :option: (or custom ones). While this would make it
possible to produce HTML that is consistent with code blocks (by adding
a bit of CSS), the source would look uglier and is harder to maintain.
(Let's say we want to add custom formatting to the [|] metacharacters
in HTML.  This is much easier with the proposed patch.)

---

[RST line blocks]: https://docutils.sourceforge.io/docs/ref/rst/restructuredtext.html#line-blocks
[backslashes in weird places]: https://github.com/fish-shell/fish-shell/pull/8626#discussion_r782837750
2022-01-19 22:56:41 +08:00

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ReStructuredText

.. _cmd-string-length:
string-length - print string lengths
====================================
Synopsis
--------
.. BEGIN SYNOPSIS
.. synopsis::
string length [-q | --quiet] [STRING ...]
.. END SYNOPSIS
Description
-----------
.. BEGIN DESCRIPTION
``string length`` reports the length of each string argument in characters. Exit status: 0 if at least one non-empty STRING was given, or 1 otherwise.
With ``-V`` or ``--visible``, it uses the visible width of the arguments. That means it will discount escape sequences fish knows about, account for $fish_emoji_width and $fish_ambiguous_width. It will also count each line (separated by ``\n``) on its own, and with a carriage return (``\r``) count only the widest stretch on a line. The intent is to measure the number of columns the STRING would occupy in the current terminal.
.. END DESCRIPTION
Examples
--------
.. BEGIN EXAMPLES
::
>_ string length 'hello, world'
12
>_ set str foo
>_ string length -q $str; echo $status
0
# Equivalent to test -n "$str"
>_ string length --visible (set_color red)foobar
# the set_color is discounted, so this is the width of "foobar"
6
>_ string length --visible 🐟🐟🐟🐟
# depending on $fish_emoji_width, this is either 4 or 8
# in new terminals it should be
8
>_ string length --visible abcdef\r123
# this displays as "123def", so the width is 6
6
>_ string length --visible a\nbc
# counts "a" and "bc" as separate lines, so it prints width for each
1
2
.. END EXAMPLES