23e25ef4

By: Tom Sydney Kerckhove <syd@cs-syd.eu>

Add comments within declarations

A comment used to be a declaration of its own, so a comment between the lines
of a transaction was either a parse error or was moved onto its own line by
the formatter.

A comment can now be written on an indented line of its own within a
declaration, where it belongs to the line below it.  That means a comment
cannot be the last line of a declaration: it would belong to no line at all,
which is an error that points at the comment.

A comment at the first column still starts a new declaration, so the lines
that a declaration cannot contain, an import, a currency, a tag, a price, an
account line and a timestamp line, hold no comments of their own: a comment
above those is a comment declaration already.

Note that the lines of a transaction are one chain of productions rather than
three lists.  The comments above a line have to be read before it is known
which kind of line follows them, so a list per kind of line makes the
description/posting and posting/extra boundaries reduce/reduce conflicts.

Fix two bugs in the process:

  * A comment whose text was only whitespace swallowed the declaration below
    it.  Nothing could match the rest of the line, so '$white+' matched the
    newline instead and left the lexer in the comment start code, reading the
    next declaration as comment text.  A comment is now a single token, so
    there is no start code left to be stranded in.

  * A description could be empty, or contain an empty line, neither of which
    can be written down: an empty description formatted to no line at all and
    was silently lost.

Timeline