rust/clippy_lints/src/eta_reduction.rs

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use clippy_utils::diagnostics::{span_lint_and_sugg, span_lint_and_then};
use clippy_utils::higher::VecArgs;
use clippy_utils::source::snippet_opt;
use clippy_utils::ty::{implements_trait, type_is_unsafe_function};
use clippy_utils::usage::UsedAfterExprVisitor;
use clippy_utils::{get_enclosing_loop_or_closure, higher};
use clippy_utils::{is_adjusted, iter_input_pats};
use if_chain::if_chain;
use rustc_errors::Applicability;
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use rustc_hir::{def_id, Expr, ExprKind, Param, PatKind, QPath};
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use rustc_lint::{LateContext, LateLintPass, LintContext};
use rustc_middle::lint::in_external_macro;
use rustc_middle::ty::{self, ClosureKind, Ty};
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use rustc_session::{declare_lint_pass, declare_tool_lint};
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declare_clippy_lint! {
/// ### What it does
/// 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 adds code for no benefit
/// and gives the optimizer more work.
///
/// ### Known problems
/// If creating the closure inside the closure has a side-
/// effect then moving the closure creation out will change when that side-
/// effect runs.
/// See [#1439](https://github.com/rust-lang/rust-clippy/issues/1439) for more details.
///
/// ### Example
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/// ```rust,ignore
/// // Bad
/// xs.map(|x| foo(x))
///
/// // Good
/// xs.map(foo)
/// ```
/// where `foo(_)` is a plain function that takes the exact argument type of
/// `x`.
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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declare_clippy_lint! {
/// ### What it does
/// Checks for closures which only invoke a method on the closure
/// argument and can be replaced by referencing the method directly.
///
/// ### Why is this bad?
/// It's unnecessary to create the closure.
///
/// ### Known problems
/// [#3071](https://github.com/rust-lang/rust-clippy/issues/3071),
/// [#3942](https://github.com/rust-lang/rust-clippy/issues/3942),
/// [#4002](https://github.com/rust-lang/rust-clippy/issues/4002)
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///
///
/// ### Example
/// ```rust,ignore
/// Some('a').map(|s| s.to_uppercase());
/// ```
/// may be rewritten as
/// ```rust,ignore
/// Some('a').map(char::to_uppercase);
/// ```
pub REDUNDANT_CLOSURE_FOR_METHOD_CALLS,
pedantic,
"redundant closures for method calls"
}
declare_lint_pass!(EtaReduction => [REDUNDANT_CLOSURE, REDUNDANT_CLOSURE_FOR_METHOD_CALLS]);
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impl<'tcx> LateLintPass<'tcx> for EtaReduction {
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
if in_external_macro(cx.sess(), expr.span) {
return;
}
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match expr.kind {
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ExprKind::Call(_, args) | ExprKind::MethodCall(_, _, args, _) => {
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for arg in args {
// skip `foo(macro!())`
if arg.span.ctxt() == expr.span.ctxt() {
check_closure(cx, arg);
}
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}
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},
_ => (),
}
}
}
fn check_closure<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
if let ExprKind::Closure(_, decl, eid, _, _) = expr.kind {
let body = cx.tcx.hir().body(eid);
let ex = &body.value;
if ex.span.ctxt() != expr.span.ctxt() {
if decl.inputs.is_empty() {
if let Some(VecArgs::Vec(&[])) = higher::vec_macro(cx, ex) {
// replace `|| vec![]` with `Vec::new`
span_lint_and_sugg(
cx,
REDUNDANT_CLOSURE,
expr.span,
"redundant closure",
"replace the closure with `Vec::new`",
"std::vec::Vec::new".into(),
Applicability::MachineApplicable,
);
}
}
// skip `foo(|| macro!())`
return;
}
if_chain!(
if let ExprKind::Call(caller, args) = ex.kind;
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if let ExprKind::Path(_) = caller.kind;
// Not the same number of arguments, there is no way the closure is the same as the function return;
if args.len() == decl.inputs.len();
// Are the expression or the arguments type-adjusted? Then we need the closure
if !(is_adjusted(cx, ex) || args.iter().any(|arg| is_adjusted(cx, arg)));
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let fn_ty = cx.typeck_results().expr_ty(caller);
if matches!(fn_ty.kind(), ty::FnDef(_, _) | ty::FnPtr(_) | ty::Closure(_, _));
if !type_is_unsafe_function(cx, fn_ty);
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if compare_inputs(&mut iter_input_pats(decl, body), &mut args.iter());
then {
span_lint_and_then(cx, REDUNDANT_CLOSURE, expr.span, "redundant closure", |diag| {
if let Some(mut snippet) = snippet_opt(cx, caller.span) {
if_chain! {
if let ty::Closure(_, substs) = fn_ty.kind();
if let ClosureKind::FnMut = substs.as_closure().kind();
if UsedAfterExprVisitor::is_found(cx, caller)
|| get_enclosing_loop_or_closure(cx.tcx, expr).is_some();
then {
// Mutable closure is used after current expr; we cannot consume it.
snippet = format!("&mut {}", snippet);
}
}
diag.span_suggestion(
expr.span,
"replace the closure with the function itself",
snippet,
Applicability::MachineApplicable,
);
}
});
}
);
if_chain!(
if let ExprKind::MethodCall(path, _, args, _) = ex.kind;
// Not the same number of arguments, there is no way the closure is the same as the function return;
if args.len() == decl.inputs.len();
// Are the expression or the arguments type-adjusted? Then we need the closure
if !(is_adjusted(cx, ex) || args.iter().skip(1).any(|arg| is_adjusted(cx, arg)));
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let method_def_id = cx.typeck_results().type_dependent_def_id(ex.hir_id).unwrap();
if !type_is_unsafe_function(cx, cx.tcx.type_of(method_def_id));
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if compare_inputs(&mut iter_input_pats(decl, body), &mut args.iter());
if let Some(name) = get_ufcs_type_name(cx, method_def_id, &args[0]);
then {
span_lint_and_sugg(
cx,
REDUNDANT_CLOSURE_FOR_METHOD_CALLS,
expr.span,
"redundant closure",
"replace the closure with the method itself",
format!("{}::{}", name, path.ident.name),
Applicability::MachineApplicable,
);
}
);
}
}
/// Tries to determine the type for universal function call to be used instead of the closure
fn get_ufcs_type_name(cx: &LateContext<'_>, method_def_id: def_id::DefId, self_arg: &Expr<'_>) -> Option<String> {
let expected_type_of_self = &cx.tcx.fn_sig(method_def_id).inputs_and_output().skip_binder()[0];
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let actual_type_of_self = &cx.typeck_results().node_type(self_arg.hir_id);
if let Some(trait_id) = cx.tcx.trait_of_item(method_def_id) {
if match_borrow_depth(expected_type_of_self, actual_type_of_self)
&& implements_trait(cx, actual_type_of_self, trait_id, &[])
{
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return Some(cx.tcx.def_path_str(trait_id));
}
}
cx.tcx.impl_of_method(method_def_id).and_then(|_| {
//a type may implicitly implement other type's methods (e.g. Deref)
if match_types(expected_type_of_self, actual_type_of_self) {
Some(get_type_name(cx, actual_type_of_self))
} else {
None
}
})
}
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fn match_borrow_depth(lhs: Ty<'_>, rhs: Ty<'_>) -> bool {
match (&lhs.kind(), &rhs.kind()) {
(ty::Ref(_, t1, mut1), ty::Ref(_, t2, mut2)) => mut1 == mut2 && match_borrow_depth(t1, t2),
(l, r) => !matches!((l, r), (ty::Ref(_, _, _), _) | (_, ty::Ref(_, _, _))),
}
}
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fn match_types(lhs: Ty<'_>, rhs: Ty<'_>) -> bool {
match (&lhs.kind(), &rhs.kind()) {
(ty::Bool, ty::Bool)
| (ty::Char, ty::Char)
| (ty::Int(_), ty::Int(_))
| (ty::Uint(_), ty::Uint(_))
| (ty::Str, ty::Str) => true,
(ty::Ref(_, t1, mut1), ty::Ref(_, t2, mut2)) => mut1 == mut2 && match_types(t1, t2),
(ty::Array(t1, _), ty::Array(t2, _)) | (ty::Slice(t1), ty::Slice(t2)) => match_types(t1, t2),
(ty::Adt(def1, _), ty::Adt(def2, _)) => def1 == def2,
(_, _) => false,
}
}
fn get_type_name(cx: &LateContext<'_>, ty: Ty<'_>) -> String {
match ty.kind() {
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ty::Adt(t, _) => cx.tcx.def_path_str(t.did),
ty::Ref(_, r, _) => get_type_name(cx, r),
_ => ty.to_string(),
}
}
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fn compare_inputs(
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closure_inputs: &mut dyn Iterator<Item = &Param<'_>>,
call_args: &mut dyn Iterator<Item = &Expr<'_>>,
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) -> bool {
for (closure_input, function_arg) in closure_inputs.zip(call_args) {
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if let PatKind::Binding(_, _, ident, _) = closure_input.pat.kind {
// XXXManishearth Should I be checking the binding mode here?
if let ExprKind::Path(QPath::Resolved(None, p)) = function_arg.kind {
if p.segments.len() != 1 {
// If it's a proper path, it can't be a local variable
return false;
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}
if p.segments[0].ident.name != ident.name {
// The two idents should be the same
return false;
}
} else {
return false;
}
} else {
return false;
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}
}
true
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}