fish-shell/doc_src/cmds/string-escape.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

string-escape - escape special characters
=========================================
Synopsis
--------
.. BEGIN SYNOPSIS
.. synopsis::
string escape [-n | --no-quoted] [--style=] [STRING ...]
string unescape [--style=] [STRING ...]
.. END SYNOPSIS
Description
-----------
.. BEGIN DESCRIPTION
``string escape`` escapes each STRING in one of three ways. The first is ``--style=script``. This is the default. It alters the string such that it can be passed back to ``eval`` to produce the original argument again. By default, all special characters are escaped, and quotes are used to simplify the output when possible. If ``-n`` or ``--no-quoted`` is given, the simplifying quoted format is not used. Exit status: 0 if at least one string was escaped, or 1 otherwise.
``--style=var`` ensures the string can be used as a variable name by hex encoding any non-alphanumeric characters. The string is first converted to UTF-8 before being encoded.
``--style=url`` ensures the string can be used as a URL by hex encoding any character which is not legal in a URL. The string is first converted to UTF-8 before being encoded.
``--style=regex`` escapes an input string for literal matching within a regex expression. The string is first converted to UTF-8 before being encoded.
``string unescape`` performs the inverse of the ``string escape`` command. If the string to be unescaped is not properly formatted it is ignored. For example, doing ``string unescape --style=var (string escape --style=var $str)`` will return the original string. There is no support for unescaping ``--style=regex``.
.. END DESCRIPTION
Examples
--------
.. BEGIN EXAMPLES
::
>_ echo \x07 | string escape
\cg
>_ string escape --style=var 'a1 b2'\u6161
a1_20_b2_E6_85_A1_
.. END EXAMPLES