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perf(transformer): reuse same UID for _this in arrow function transform #5840

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perf(transformer): reuse same UID for _this in arrow function transform #5840

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99 changes: 69 additions & 30 deletions crates/oxc_transformer/src/es2015/arrow_functions.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -61,12 +61,17 @@

use oxc_allocator::Vec;
use oxc_ast::{ast::*, NONE};
use oxc_span::SPAN;
use oxc_syntax::{scope::ScopeFlags, symbol::SymbolFlags};
use oxc_span::{CompactStr, SPAN};
use oxc_syntax::{
node::NodeId,
reference::ReferenceFlags,
scope::ScopeFlags,
symbol::{SymbolFlags, SymbolId},
};
use oxc_traverse::{Traverse, TraverseCtx};
use serde::Deserialize;

use crate::{context::Ctx, helpers::bindings::BoundIdentifier};
use crate::context::Ctx;

#[derive(Debug, Default, Clone, Deserialize)]
pub struct ArrowFunctionsOptions {
Expand All @@ -81,7 +86,8 @@ pub struct ArrowFunctionsOptions {
pub struct ArrowFunctions<'a> {
ctx: Ctx<'a>,
_options: ArrowFunctionsOptions,
this_var_stack: std::vec::Vec<Option<BoundIdentifier<'a>>>,
this_var_name: Option<Atom<'a>>,
this_var_symbol_ids_stack: std::vec::Vec<Option<SymbolId>>,
/// Stack to keep track of whether we are inside an arrow function or not.
inside_arrow_function_stack: std::vec::Vec<bool>,
}
Expand All @@ -91,8 +97,9 @@ impl<'a> ArrowFunctions<'a> {
Self {
ctx,
_options: options,
this_var_name: None,
// Initial entries for `Program` scope
this_var_stack: vec![None],
this_var_symbol_ids_stack: vec![None],
inside_arrow_function_stack: vec![false],
}
}
Expand All @@ -103,16 +110,16 @@ impl<'a> Traverse<'a> for ArrowFunctions<'a> {
fn exit_program(&mut self, program: &mut Program<'a>, _ctx: &mut TraverseCtx<'a>) {
debug_assert!(self.inside_arrow_function_stack.len() == 1);

assert!(self.this_var_stack.len() == 1);
let this_var = self.this_var_stack.pop().unwrap();
if let Some(this_var) = this_var {
self.insert_this_var_statement_at_the_top_of_statements(&mut program.body, &this_var);
assert!(self.this_var_symbol_ids_stack.len() == 1);
let symbol_id = self.this_var_symbol_ids_stack.pop().unwrap();
if let Some(symbol_id) = symbol_id {
self.insert_this_var_statement_at_the_top_of_statements(&mut program.body, symbol_id);
}
}

fn enter_function(&mut self, func: &mut Function<'a>, _ctx: &mut TraverseCtx<'a>) {
if func.body.is_some() {
self.this_var_stack.push(None);
self.this_var_symbol_ids_stack.push(None);
self.inside_arrow_function_stack.push(false);
}
}
Expand All @@ -133,11 +140,11 @@ impl<'a> Traverse<'a> for ArrowFunctions<'a> {
return;
};

let this_var = self.this_var_stack.pop().unwrap();
if let Some(this_var) = this_var {
let symbol_id = self.this_var_symbol_ids_stack.pop().unwrap();
if let Some(symbol_id) = symbol_id {
self.insert_this_var_statement_at_the_top_of_statements(
&mut body.statements,
&this_var,
symbol_id,
);
}

Expand Down Expand Up @@ -246,24 +253,52 @@ impl<'a> ArrowFunctions<'a> {
span: Span,
ctx: &mut TraverseCtx<'a>,
) -> IdentifierReference<'a> {
let this_var = self.this_var_stack.last_mut().unwrap();
if this_var.is_none() {
let target_scope_id =
ctx.scopes().ancestors(ctx.current_scope_id()).skip(1).find(|&scope_id| {
let symbol_id_ref = self.this_var_symbol_ids_stack.last_mut().unwrap();
let (this_atom, symbol_id) = if let Some(symbol_id) = symbol_id_ref {
// Symbol for `_this` in this scope has already been created
let this_atom = self.this_var_name.as_ref().unwrap().clone();
(this_atom, *symbol_id)
} else {
// No symbol for `_this` in this scope.
// Create UID for `_this` if not already created.
let (this_atom, this_compact_str) = if let Some(this_var_name) = &self.this_var_name {
let this_atom = this_var_name.clone();
let this_compact_str = CompactStr::from(this_atom.as_str());
(this_atom, this_compact_str)
} else {
let this_compact_str = ctx.generate_uid_name("this");
let this_atom = ctx.ast.atom(&this_compact_str);
self.this_var_name = Some(this_atom.clone());
(this_atom, this_compact_str)
};

// Create symbol and record it for later
let scope_id = ctx
.scopes()
.ancestors(ctx.current_scope_id())
.skip(1)
.find(|&scope_id| {
let scope_flags = ctx.scopes().get_flags(scope_id);
scope_flags.intersects(ScopeFlags::Function | ScopeFlags::Top)
&& !scope_flags.contains(ScopeFlags::Arrow)
});
})
.unwrap();

this_var.replace(BoundIdentifier::new_uid(
"this",
target_scope_id.unwrap(),
let symbol_id = ctx.symbols_mut().create_symbol(
SPAN,
this_compact_str.clone(),
SymbolFlags::FunctionScopedVariable,
ctx,
));
}
let this_var = this_var.as_ref().unwrap();
this_var.create_spanned_read_reference(span, ctx)
scope_id,
NodeId::DUMMY,
);
ctx.scopes_mut().add_binding(scope_id, this_compact_str, symbol_id);

*symbol_id_ref = Some(symbol_id);

(this_atom, symbol_id)
};

ctx.create_bound_reference_id(span, this_atom, symbol_id, ReferenceFlags::Read)
}

fn transform_arrow_function_expression(
Expand Down Expand Up @@ -308,12 +343,16 @@ impl<'a> ArrowFunctions<'a> {
fn insert_this_var_statement_at_the_top_of_statements(
&mut self,
statements: &mut Vec<'a, Statement<'a>>,
this_var: &BoundIdentifier<'a>,
symbol_id: SymbolId,
) {
let binding_id = BindingIdentifier::new_with_symbol_id(
SPAN,
self.this_var_name.as_ref().unwrap().clone(),
symbol_id,
);

let binding_pattern = self.ctx.ast.binding_pattern(
self.ctx
.ast
.binding_pattern_kind_from_binding_identifier(this_var.create_binding_identifier()),
self.ctx.ast.binding_pattern_kind_from_binding_identifier(binding_id),
NONE,
false,
);
Expand Down
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