This makes it so code like
```fish
echo foo
echo bar
```
is collapsed into
```fish
echo foo
echo bar
```
One empty line is allowed, more is overkill.
We could also allow more than one for e.g. function endings.
This would crash from the highlighter for something like
`PATH={$PATH[echo " "`
The underlying cause is that we use "char_at" which panics on
overread.
So instead this implements try_char_at and then just returns None.
In many cases we currently discard escaped newlines, since they
are often unnecessary (when used around &|;). Escaped newlines
are useful for structuring argument lists. Allow them for variable
assignments since they are similar.
Closes#7955
fish_indent used to increment the indentation level whenever we saw an escaped
newline. This broke because of recent changes to parse_util_compute_indents().
Since parse_util_compute_indents() function already indents continuations
there is not much to do for fish_indent - we can simply query the indentation
level of the newline. Reshuffle the code since we need to pass the offset
of the newline. Maybe this can even be simplified further.
Fixes#7720
It could be nice to use a heuristic for this in future, but for now let's
stick to the old behavior so we can keep formatting scripts without occasional
bad formatting changes.
A heuristic could also be used to break lines after |, && or || but I don't
think there is much need for that at the moment.
Closes#7252
This indents continuations after pipes and conjunctions if they contain
a newline.
Example:
cmd1 &&
cmd2
But it avoids the "double indent" if it indented unconditionally:
cmd1 | begin
cmd2
end
More work towards improving #7252
Prior to this change, when emitting gap text (comments, newlines, etc),
fish_indent would use the indentation of the text at the end of the gap.
But this has the wrong result for this case:
begin
command
# comment
end
as the comment would get the indent of the 'end'. Instead use the indent
computed for the gap text itself.
Addresses one case of #7252.
This switches fish_indent from parsing with parse_tree
to the new ast.
This is the most difficult transition because the new ast retains less
lexical information than the old parse tree. The strategy is:
1. Use parse_util_compute_indents to compute indenting for each token.
2. Compute the "gap text" between the text of significant tokens. This
contains whitespace, comments, etc.
3. "Fix up" the gap text while leaving the significant tokens alone.
This isn't quite the old-style test, but it checks some of the line
continuation stuff.
Note that littlecheck ignores leading whitespace, so testing the
actual indentation requires some more effort.
