use oxc_ast::ast::Program;
use oxc_ast_visit::Visit;
use oxc_semantic::Semantic;
use crate::rules::{Rule, RuleFinding, RuleMeta, Severity};
pub struct NoHeavyComputationInRender;
const RULE_META: RuleMeta = RuleMeta {
id: "no-heavy-computation-in-render",
default_severity: Severity::Warning,
category: "performance",
description: "Avoid heavy synchronous computation in render",
};
const HEAVY_METHODS: &[&str] = &[
"sort",
"filter",
"map",
"reduce",
"forEach",
"toSorted",
"toReversed",
];
impl Rule for NoHeavyComputationInRender {
fn meta(&self) -> &RuleMeta {
&RULE_META
}
fn run(&self, program: &Program, _semantic: &Semantic, source_text: &str) -> Vec<RuleFinding> {
let mut collector = HeavyComputeCollector {
findings: Vec::new(),
source: source_text,
depth: 0,
};
collector.visit_program(program);
collector.findings
}
}
struct HeavyComputeCollector<'a> {
findings: Vec<RuleFinding>,
source: &'a str,
depth: usize,
}
impl<'a> HeavyComputeCollector<'a> {
fn add_finding(&mut self, start: usize, msg: String) {
let line = self.source[..start].lines().count().max(1);
let col = start - self.source[..start].rfind('\n').map(|i| i + 1).unwrap_or(0);
self.findings.push(RuleFinding {
line,
column: col + 1,
message: msg,
});
}
}
impl<'a> Visit<'a> for HeavyComputeCollector<'a> {
fn visit_call_expression(&mut self, expr: &oxc_ast::ast::CallExpression<'a>) {
if let Some(member) = expr.callee.as_member_expression()
&& let Some(name) = member.static_property_name()
&& HEAVY_METHODS.contains(&name)
&& self.depth > 0
{
self.add_finding(
expr.span.start as usize,
format!("`.{name}()` creates a new array on every render — memoize with useMemo"),
);
}
}
fn visit_function(
&mut self,
func: &oxc_ast::ast::Function<'a>,
_flags: oxc_syntax::scope::ScopeFlags,
) {
let was = self.depth;
self.depth += 1;
oxc_ast_visit::walk::walk_function(self, func, _flags);
self.depth = was;
}
fn visit_arrow_function_expression(
&mut self,
func: &oxc_ast::ast::ArrowFunctionExpression<'a>,
) {
let was = self.depth;
self.depth += 1;
oxc_ast_visit::walk::walk_arrow_function_expression(self, func);
self.depth = was;
}
}