As the name suggests, the qapi2texi script converts JSON QAPI
description into a texi file suitable for different target
formats (info/man/txt/pdf/html...).

It parses the following kind of blocks:

Free-form:

  ##
  # = Section
  # == Subsection
  #
  # Some text foo with *emphasis*
  # 1. with a list
  # 2. like that
  #
  # And some code:
  # | $ echo foo
  # | -> do this
  # | <- get that
  #
  ##

Symbol description:

  ##
  # @symbol:
  #
  # Symbol body ditto ergo sum. Foo bar
  # baz ding.
  #
  # @param1: the frob to frobnicate
  # @param2: #optional how hard to frobnicate
  #
  # Returns: the frobnicated frob.
  #          If frob isn't frobnicatable, GenericError.
  #
  # Since: version
  # Notes: notes, comments can have
  #        - itemized list
  #        - like this
  #
  # Example:
  #
  # -> { "execute": "quit" }
  # <- { "return": {} }
  #
  ##

That's roughly following the following EBNF grammar:

api_comment = "##\n" comment "##\n"
comment = freeform_comment | symbol_comment
freeform_comment = { "# " text "\n" | "#\n" }
symbol_comment = "# @" name ":\n" { member | tag_section | freeform_comment }
member = "# @" name ':' [ text ] "\n" freeform_comment
tag_section = "# " ( "Returns:", "Since:", "Note:", "Notes:", "Example:", "Examples:" ) [ text ]  "\n" freeform_comment
text = free text with markup

Note that the grammar is ambiguous: a line "# @foo:\n" can be parsed
both as freeform_comment and as symbol_comment.  The actual parser
recognizes symbol_comment.

See docs/qapi-code-gen.txt for more details.

Deficiencies and limitations:
- the generated QMP documentation includes internal types
- union type support is lacking
- type information is lacking in generated documentation
- doc comment error message positions are imprecise, they point
  to the beginning of the comment.
- a few minor issues, all marked TODO/FIXME in the code
Signed-off-by: NMarc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20170113144135.5150-16-marcandre.lureau@redhat.com>
Reviewed-by: NMarkus Armbruster <armbru@redhat.com>
[test-qapi.py tweaked to avoid trailing empty lines in .out]
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>

The handling of \ inside QAPI strings was less than ideal, and
really only worked JSON's \/, \\, \", and our extension of \'
(an obvious extension, when you realize we use '' instead of ""
for strings).  For other things, like '\n', it resulted in a
literal 'n' instead of a newline.

Of course, at the moment, we really have no use for escaped
characters, as QAPI has to map to C identifiers, and we currently
support ASCII only for that.  But down the road, we may add
support for default values for string parameters to a command
or struct; if that happens, it would be nice to correctly support
all JSON escape sequences, such as \n or \uXXXX.  This gets us
closer, by supporting Unicode escapes in the ASCII range.

Since JSON does not require \OCTAL or \xXX escapes, and our QMP
implementation does not understand them either, I intentionally
reject it here, but it would be an easy addition if we desired it.
Likewise, intentionally refusing the NUL byte means we don't have
to worry about C strings being shorter than the qapi input.
Signed-off-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NMarkus Armbruster <armbru@redhat.com>
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>