use rustc::lint::*; use rustc::middle::ty; use rustc_front::hir::*; use utils::{snippet_opt, span_lint_and_then, is_adjusted}; #[allow(missing_copy_implementations)] pub struct EtaPass; /// **What it does:** This lint checks for closures which just call another function where the function can be called directly. `unsafe` functions or calls where types get adjusted are ignored. /// /// **Why is this bad?** Needlessly creating a closure just costs heap space and adds code for no benefit. /// /// **Known problems:** None /// /// **Example:** `xs.map(|x| foo(x))` where `foo(_)` is a plain function that takes the exact argument type of `x`. declare_lint! { pub REDUNDANT_CLOSURE, Warn, "using redundant closures, i.e. `|a| foo(a)` (which can be written as just `foo`)" } impl LintPass for EtaPass { fn get_lints(&self) -> LintArray { lint_array!(REDUNDANT_CLOSURE) } } impl LateLintPass for EtaPass { fn check_expr(&mut self, cx: &LateContext, expr: &Expr) { match expr.node { ExprCall(_, ref args) | ExprMethodCall(_, _, ref args) => { for arg in args { check_closure(cx, arg) } } _ => (), } } } fn check_closure(cx: &LateContext, expr: &Expr) { if let ExprClosure(_, ref decl, ref blk) = expr.node { if !blk.stmts.is_empty() { // || {foo(); bar()}; can't be reduced here return; } if let Some(ref ex) = blk.expr { if let ExprCall(ref caller, ref args) = ex.node { if args.len() != decl.inputs.len() { // Not the same number of arguments, there // is no way the closure is the same as the function return; } if is_adjusted(cx, ex) || args.iter().any(|arg| is_adjusted(cx, arg)) { // Are the expression or the arguments type-adjusted? Then we need the closure return; } let fn_ty = cx.tcx.expr_ty(caller); match fn_ty.sty { // Is it an unsafe function? They don't implement the closure traits ty::TyFnDef(_, _, fn_ty) | ty::TyFnPtr(fn_ty) => { if fn_ty.unsafety == Unsafety::Unsafe { return; } } _ => (), } for (ref a1, ref a2) in decl.inputs.iter().zip(args) { if let PatKind::Ident(_, ident, _) = a1.pat.node { // XXXManishearth Should I be checking the binding mode here? if let ExprPath(None, ref p) = a2.node { if p.segments.len() != 1 { // If it's a proper path, it can't be a local variable return; } if p.segments[0].identifier != ident.node { // The two idents should be the same return; } } else { return; } } else { return; } } span_lint_and_then(cx, REDUNDANT_CLOSURE, expr.span, "redundant closure found", |db| { if let Some(snippet) = snippet_opt(cx, caller.span) { db.span_suggestion(expr.span, "remove closure as shown:", snippet); } }); } } } }