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Joe Savona
0c1193ecd7
This is meant to replace the initial `estree` crate with a version that is
generated from a JSON description of ESTree. The idea is to make it easy to
experiment with slightly different representations to balance ergonomic usage of
the data at runtime with serialization compatible with ESTree spec. The JSON
schema looks like this (somewhat abbreviated):
```
{
// Objects are struct types that don't have a `type` and can't appear as an enum
variant
objects: {
Position: {
line: {type: "NonZeroU32"},
column: {type: "u32"}
},
...
},
// Nodes are struct types with a `type` and which can appear as enum variants
(statements, expressions, patterns, etc)
nodes: {
ArrayExpression: {
elements: {
type: "Expression",
plural: true,
nullable_item: true,
}
}
...
},
// Categories of nodes with multiple variants, represented as enums.
// Can be recursive, eg ForInit can be VariableDeclaration or Expression,
// where Expression is also an enum
enums: {
Expression: [
"ArrayExpression",
...
]
},
// Simple enums which have a corresponding string value. Used primarily for
operators (binary/unary/logical/etc)
// but also for things like variable declaration kind (var/const/let)
operators: {
BinaryOperator: {
Plus: "+",
Instanceof: "instanceof",
}
}
}
```
The core estree files are now generated using Cargo's build script mechanism.
Right now i only defined the types and fields from ES5, so i'll have to flush
out the rest of the modern JS spec and extensions like JSX, TypeScript, and
Flow. But already the for-statement example works, showing that this approach
can handle complex cases such as unions of types or other unions (ForStatement
initializer is tricky bc it can be a VariableDeclaration or an Expression - that
works now!).
This is still WIP a bit - now that the ESTree definition is more precise i can
go back and clean up some other code (have to, because the swc -> estree
conversion needs some tweaks now).