mirror of
https://github.com/rust-lang/rust-clippy
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119 lines
4.6 KiB
Rust
119 lines
4.6 KiB
Rust
// Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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use crate::rustc::hir::*;
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use crate::rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
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use crate::rustc::ty;
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use crate::rustc::{declare_tool_lint, lint_array};
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use crate::rustc_errors::Applicability;
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use crate::utils::{is_adjusted, iter_input_pats, snippet_opt, span_lint_and_then};
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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:** If creating the closure inside the closure has a side-
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/// effect then moving the closure creation out will change when that side-
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/// effect runs.
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/// See https://github.com/rust-lang/rust-clippy/issues/1439 for more
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/// details.
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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_clippy_lint! {
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pub REDUNDANT_CLOSURE,
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style,
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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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ExprKind::Call(_, ref args) | ExprKind::MethodCall(_, _, ref args) => {
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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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}
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fn check_closure(cx: &LateContext<'_, '_>, expr: &Expr) {
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if let ExprKind::Closure(_, 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 ExprKind::Call(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::FnDef(..) | ty::FnPtr(_) => {
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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::Never {
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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 ExprKind::Path(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].ident.name != ident.name {
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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_with_applicability(
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expr.span,
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"remove closure as shown",
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snippet,
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Applicability::MachineApplicable,
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);
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}
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});
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}
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}
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}
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