Track "delayed" annotations in the semantic model #5070
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…ng (#5074) ## Summary This PR enables autofix behavior for the `flake8-pyi` rule that asks you to alias `Set` to `AbstractSet` when importing `collections.abc.Set`. It's not the most important rule, but it's a good isolated test-case for local symbol renaming. The renaming algorithm is outlined in-detail in the `renamer.rs` module. But to demonstrate the behavior, here's the diff when running this fix over a complex file that exercises a few edge cases: ```diff --- a/foo.pyi +++ b/foo.pyi @@ -1,16 +1,16 @@ if True: - from collections.abc import Set + from collections.abc import Set as AbstractSet else: - Set = 1 + AbstractSet = 1 -x: Set = set() +x: AbstractSet = set() -x: Set +x: AbstractSet -del Set +del AbstractSet def f(): - print(Set) + print(AbstractSet) def Set(): pass ``` Making this work required resolving a bunch of edge cases in the semantic model that were causing us to "lose track" of references. For example, the above wasn't possible with our previous approach to handling deletions (#5071). Similarly, the `x: Set` "delayed annotation" tracking was enabled via #5070. And many of these edits would've failed if we hadn't changed `BindingKind` to always match the identifier range (#5090). So it's really the culmination of a bunch of changes over the course of the week. The main outstanding TODO is that this doesn't support `global` or `nonlocal` usages. I'm going to take a look at that tonight, but I'm comfortable merging this as-is. Closes #1106. Closes #5091.
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Summary
This PR tackles a corner case that we'll need to support local symbol renaming. It relates to a nuance in how we want handle annotations (i.e.,
AnnAssignstatements with no value, likex: intin a function body).When we see a statement like:
We create a
BindingKind::Annotationforx. This is a specialBindingKindthat the resolver isn't allowed to return. For example, given:The second line will yield an
undefined-nameerror.So why does this
BindingKindexist at all? In Pyflakes, to support theunused-annotationlint:If we don't track
BindingKind::Annotation, we can't lint for unused variables that are only "defined" via annotations.There are a few other wrinkles to
BindingKind::Annotation. One is that, if a binding already exists in the scope, we actually just discard theBindingKind. So in this case:When we go to create the
BindingKind::Annotationfor the second statement, we notice that (1) we're creating an annotation but (2) the scope already has binding for the name -- so we just drop the binding on the floor. This has the nice property that annotations aren't considered to "shadow" another binding, which is important in a bunch of places (e.g., if we haveimport os; os: int, we still considerosto be an import, as we should). But it also means that these "delayed" annotations are one of the few remaining references that we don't track anywhere in the semantic model.This PR adds explicit support for these via a new
delayed_annotationsattribute on the semantic model. These should be extremely rare, but we do need to track them if we want to support local symbol renaming.This isn't the right way to model this
This isn't the right way to model this.
Here's an alternative:
BindingKind::Annotation, and treat annotations as their own, separate concept.BindingIdon eachScope, store a map from name to...SymbolId.Symbolabstraction, where a symbol can point to a current binding, and a list of annotations, like:If we did this, we could appropriately model the semantics described above. When we go to resolve a binding, we ignore annotations (always). When we try to find unused variables, we look through the list of symbols, and have sufficient information to discriminate between annotations and bound variables. Etc.
The main downside of this
Symbol-based approach is that it's going to take a lot more work to implement, and it'll be less performant (we'll be storing more data per symbol, and our binding lookups will have an added layer of indirection).