feat(traverse): introduce MaybeBoundIdentifier

[overlookmotel]

MaybeBoundIdentifier is similar to BoundIdentifier, but can be used where the identifier may or may not have have a SymbolId (may or may not be bound).

Typical usage:

// Create `MaybeBoundIdentifier` from an existing `IdentifierReference`
let binding = MaybeBoundIdentifier::from_identifier_reference(ident, ctx);

// Generate `IdentifierReference`s and insert them into AST
assign_expr.left = binding.create_write_target(ctx);
assign_expr.right = binding.create_read_expression(ctx);

[graphite-app]

Your org has enabled the Graphite merge queue for merging into main

Add the label “0-merge” to the PR and Graphite will automatically add it to the merge queue when it’s ready to merge. Or use the label “hotfix” to add to the merge queue as a hot fix.

You must have a Graphite account and log in to Graphite in order to use the merge queue. Sign up using this link.

[overlookmotel]

• refactor(traverse)!: remove TraverseCtx::clone_identifier_reference #7266
• feat(traverse): introduce MaybeBoundIdentifier #7265 👈
• main

This stack of pull requests is managed by Graphite. Learn more about stacking.

Join @overlookmotel and the rest of your teammates on Graphite

[codspeed-hq]

CodSpeed Performance Report

Merging #7265 will not alter performance

_{Comparing 11-13-feat_traverse_introduce_maybeboundidentifier_ (8c754b1) with main (de472ca)}

Summary

✅ 30 untouched benchmarks

[overlookmotel]

@Boshen This API is intended for your spread transform use case.

[Boshen]

Confirmed working as intended.

        let maybe_bound_identifier = if let Expression::Identifier(ident) = init {
            MaybeBoundIdentifier::from_identifier_reference(ident, ctx)
        } else {
            let bound_identifier =
                ctx.generate_uid_in_current_scope_based_on_node(init, builder.symbol_flags);
            let id = bound_identifier.create_binding_pattern(ctx);
            let init = ctx.ast.move_expression(init);
            builder.decls.push(ctx.ast.variable_declarator(SPAN, decl.kind, id, Some(init), false));
            bound_identifier.to_maybe_bound_identifier()
        };

[graphite-app]

Merge activity

• Nov 13, 10:11 AM EST: A user added this pull request to the Graphite merge queue.
• Nov 13, 10:17 AM EST: A user merged this pull request with the Graphite merge queue.

[overlookmotel]

What's odd is that in all the other transforms, Babel generates a temp var for unbound identifiers, because accessing a global x can have side effects if global.x is a getter.

e.g. Babel REPL

Not sure why that's not the case in the rest/spread transform. Strictly speaking, it's a bug.