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