2175e2f573
This CL adds three new functions to the types2 API to support lazy import resolution: 1. A new Scope.InsertLazy method to allow recording that Objects exist in a particular Scope (in particular, package scopes) without having to yet fully construct those objects. Instead, types2 will call the provided `resolve` function if/when the object is actually needed. 2. Similarly, a new NewTypeNameLazy function to create TypeName objects without yet instantiating their underlying Named instance. 3. Finally, an InstantiateLazy method, that allows creating type instances without requiring any of the types to be expanded right away. Importantly, this requires providing a types2.Checker argument to handle recursive types correctly. The APIs as-is are a bit clumsy (esp. NewTypeNameLazy), but seem to work well for cmd/compile's needs. In particular, they simplify some of the complexities of handling recursive type definitions within the importer. Also, the current prototype is a bit fragile. It uses sync.Once to manage concurrent lazy resolution, which is frustrating to debug in the presence of reentrancy issues. It also means the importer needs to deal with concurrency as well. These aren't issues for types2 though as cmd/compile only walks the type-checked AST sequentially. Finally, it looks like some of the details of lazy type names are similar to the lazy "instance" stuff used for generics, so maybe there's opportunity for unifying them under a more general (but still internal) lazy type mechanism. I had originally intended for this CL to also update the types2 importer, but (1) it doesn't have access to the types2.Checker instance needed to call InstantiateLazy, and (2) it creates a new TypeName/TypeParam at each use rather than reusing them, which evidently works with types2.Instantiate but not types2.(*Checker).instantiate (i.e., InstantiateLazy). I spent a while trying to fix these issues, but kept running into more subtle issues. Instead, I've included my WIP "unified IR" CL as a followup CL that demonstrates these Lazy methods (see noder/reader2.go). Updates #46449. Change-Id: I4d1e8e649f6325a11790d25fd90c39fa07c8d41d Reviewed-on: https://go-review.googlesource.com/c/go/+/323569 Run-TryBot: Matthew Dempsky <mdempsky@google.com> Trust: Matthew Dempsky <mdempsky@google.com> Trust: Robert Griesemer <gri@golang.org> TryBot-Result: Go Bot <gobot@golang.org> Reviewed-by: Robert Griesemer <gri@golang.org> |
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