This avoids creating refcounted strings during evaluation and makes it
easier to use the same parsed string in multiple places (should be
useful once we implement functions).
If you assign into a member access (`foo.bar = baz` or `foo@bar = baz`), it
is no longer permitted that the LHS of the at/dot is an arbitrary
assignable. It now must be a variable, at or dot. This disallows some silly
constructs (e.g. `[foo]@bar = baz`), increases the similarity to function
parameters and should make writing the evaluation code for these more easy.
The previous representation didn't properly model the fact that an
assignable / parameter can only be expanded, if it's a list element. This
now better models this. Other than being more correct, this should also
make evaluating these a bit easier.
While I was at it, I also improved the error message for multiple
expansions on the same level and added tests for these.
This replaces the grow_cap function with the ensure_cap family of
functions, as they actually do what you want: You'll likely not want to
blindly increase the capacity of a growable, but you want to make sure that
the capacity is large enough to hold the elements you're about to insert.
- Simplify return types: Many functions that returned
`enum parse_fragment_result` only ever returned PF_OK or PF_ERROR.
Changing these functions to return bool simplifies things a lot. This
also helped in identifying some places where I didn't handle all
parse_fragment_result values properly.
- More cleaning up
- Allow linebreaks inside parenthesis
