If just one of the range ends is negative, this now forces direction away from it.
I.e. if the beginning is negative, we go in reverse.
If the end is negative, we go forwards.
This fixes cases like
$var[2..-1]
if $var only has one element.
This just removes every invalid index.
That means with `set foo a b c` and the "show" function from tests/expand.in:
- `show $foo[-5..-1]` prints "3 a b c"
- `show $foo[-10..1]` prints "1 a"
- `show $foo[2..5]` prints "2 b c"
- `show $foo[1 3 7 2]` prints "3 a c b"
and similar for command substitutions.
Fixes#826.
When a variable is parsed as being empty, parse out the slice and
validate the indexes anyway, behaving for slicing purposes as if the
variable had a single empty value.
Besides providing errors when expected, this also fixes the following:
set -l foo
echo "$foo[1]"
This used to print "[1]", now it properly prints nothing.
Double expansions of variables had the following issues:
* `"$$foo"` threw an error no matter what the value of `$foo` was.
* `set -l foo ''; echo $$foo` threw an error because of the expansion of
`$foo` to `''`.
With this change, double expansion always works properly. When
double-expanding a multi-valued variable, in a double-quoted string the
first word of the inner expansion is used for the outer expansion, and
outside of a quoted string every word is used for the double-expansion
in each of the arguments.
> set -l foo bar baz
> set -l bar one two
> set -l baz three four
> echo "$$foo"
one two baz
> echo $$foo
one two three four
