Turns out, `(_)` would match both named and unnamed nodes, as we never
checked the value of the `match_unnamed` field. This is the real reason
why the final catch-all rule we removed in the last commit was
superfluous -- unnamed nodes were being caught by the penultimate rule
instead (and mapped to `unsupported_node`).
Having fixed the bug, we now (correctly) get errors due to unmatched
unnamed nodes in the input. To fix this, we change the catch-all rule to
match unnamed nodes as well. This restores the previous behaviour
exactly.
At some point, we should find a better way to handle unnamed nodes, as
it seems wasteful to map these to `unsupported_node` (since we in
practice only use them for their string content). Perhaps we should not
attempt to translate unnamed nodes at all?
In order to facilitate static type checking of rules (and to make it
easier for human readers as well), rust blocks at the root level (i.e.
rules of the form `... => { ... }`) must now have a type annotation in
front.
All other forms are unaffected: if the right hand side of a rule is a
tree, we can read the type of the root node directly. For interpolations
that happen inside of such a tree, we can recover the type by looking at
what field we're interpolating into, and consulting the output schema.
All existing uses have been updated to have the appropriate type
annotations, though these are of course not checked yet (and so could be
wrong).
Finally, this commit also removes the final catch-all rule `_ @node =>
{node}`. Because of the preceding rule that matches `(_) @node`, this
rule would only ever match unnamed nodes, and I think in practice it did
not match at all (at least not in our current set of tests).
To give it a proper type we would have to add some notion of an "any"
type, which I would like to avoid. If it _does_ turn out to be needed,
we can easily add it back (ideally with a test-case that shows why it's
still needed).
This macro allows the easy addition of multiple rules at the same time.
In addition, it also accepts an input and output schema, which
eventually will be used to check the validity of the rewrite rules.
For type checking rules, we need to be able to load schemas (so we know
what to check against). However, since we can't have yeast-macros
depending on yeast (where the schema-handling code currently lives) as
this would introduce a circular dependency, we instead split the
schema-related code into its own yeast-schema crate.
In order to avoid having context changes bubble up through the tree (or
from one sibling to another) the current framework makes a copy of the
context before calling `translate` recursively, and then restores it
afterwards.
However, this is a bit silly -- after we're done with all of the
translations, there's really no need to restore the context (as it
doesn't get accessed again).
So instead we change it from "save and then restore" to "clone and then
drop". Each rule invocation gets its own copy of the context, and simply
drops it when it's done.
A previous commit added a translate_reset method on BuildCtx, which had
the effect of performing a translation in a completely empty context.
One issue with this is that this is an all-or-nothing proposition -- If
you want to preserve _some_ parts of the context, you have to do
something more complicated. Moreover, if you introduce a contextual
value that _should_ be preserved, all of the existing uses of
translate_reset now silently do the wrong thing.
There are two patterns that we want to address. The first one is "modify
the context in some way, then do a translation". If the translation is
the last step of a Rust block, then we don't actually need
translate_reset -- we could just reset the context and then call
`translate`. The fact that the outer context is restored afterwards
means it's okay to make destructive changes to `ctx.user_ctx` -- none of
these changes will persist.
The second pattern is the same, but where we want to do more
translations using the original context, after having performed a
translation with a modified context. In this case, we cannot just
overwrite the context, since that would invalidate the subsequent
translations.
Instead, we introduce a new method `ctx.scoped` which takes a closure as
an argument. With this we can now write
```
ctx.scoped(|ctx| ctx.reset(); ctx.translate(...));
```
and the closure is run with a copy of `ctx` that has a clone of
`user_ctx` on the inside, so no changes will persist.
(You may wonder: why not just clone `ctx` and use the clone? The answer
is that `ctx` owns mutable pointers to the AST etc., and this makes it
awkward to just "clone" it. The closure circumvents this issue nicely,
since it can borrow these pointers internally.)
For now, this rewrite has the same behaviour as the version that used
translate_reset -- we clear the entire `user_ctx`. However, we could
imagine being more fine-grained in this approach, by implementing, say,
SwiftContext::reset_modifiers (which would only affect what modifiers
are currently in the context, leaving everything else as-is).
There's an awkward divide in yeast between returning a list of nodes or
optional node (both of which are iterable), and returning a single node
(which is not). In practice, we would like all of these cases to be
handled transparently: if a single node is returned, it behaves as if it
were a singleton list containing that node. This gives us a uniform
interface during translation -- no matter what is returned, it will be
an iterable of nodes.
To facilitate this, we make the slightly unorthodox choice of
implementing IntoIterator for Id, with the behaviour detailed above.
Note that when a line is marked `// BAD [NOT DETECTED]` but actually has
an alert, I assume that the `[NOT DETECTED]` is outdated and should be
deleted.
