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|
use crate::lints::MappingToUnit;
use crate::{LateContext, LateLintPass, LintContext};
use rustc_hir::{Expr, ExprKind, HirId, Stmt, StmtKind};
use rustc_middle::{
query::Key,
ty::{self, Ty},
};
declare_lint! {
/// The `map_unit_fn` lint checks for `Iterator::map` receive
/// a callable that returns `()`.
///
/// ### Example
///
/// ```rust
/// fn foo(items: &mut Vec<u8>) {
/// items.sort();
/// }
///
/// fn main() {
/// let mut x: Vec<Vec<u8>> = vec![
/// vec![0, 2, 1],
/// vec![5, 4, 3],
/// ];
/// x.iter_mut().map(foo);
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Mapping to `()` is almost always a mistake.
pub MAP_UNIT_FN,
Warn,
"`Iterator::map` call that discard the iterator's values"
}
declare_lint_pass!(MapUnitFn => [MAP_UNIT_FN]);
impl<'tcx> LateLintPass<'tcx> for MapUnitFn {
fn check_stmt(&mut self, cx: &LateContext<'tcx>, stmt: &Stmt<'_>) {
if stmt.span.from_expansion() {
return;
}
if let StmtKind::Semi(expr) = stmt.kind {
if let ExprKind::MethodCall(path, receiver, args, span) = expr.kind {
if path.ident.name.as_str() == "map" {
if receiver.span.from_expansion()
|| args.iter().any(|e| e.span.from_expansion())
|| !is_impl_slice(cx, receiver)
|| !is_diagnostic_name(cx, expr.hir_id, "IteratorMap")
{
return;
}
let arg_ty = cx.typeck_results().expr_ty(&args[0]);
let default_span = args[0].span;
if let ty::FnDef(id, _) = arg_ty.kind() {
let fn_ty = cx.tcx.fn_sig(id).skip_binder();
let ret_ty = fn_ty.output().skip_binder();
if is_unit_type(ret_ty) {
cx.emit_spanned_lint(
MAP_UNIT_FN,
span,
MappingToUnit {
function_label: cx
.tcx
.span_of_impl(*id)
.unwrap_or(default_span),
argument_label: args[0].span,
map_label: arg_ty.default_span(cx.tcx),
suggestion: path.ident.span,
replace: "for_each".to_string(),
},
)
}
} else if let ty::Closure(id, subs) = arg_ty.kind() {
let cl_ty = subs.as_closure().sig();
let ret_ty = cl_ty.output().skip_binder();
if is_unit_type(ret_ty) {
cx.emit_spanned_lint(
MAP_UNIT_FN,
span,
MappingToUnit {
function_label: cx
.tcx
.span_of_impl(*id)
.unwrap_or(default_span),
argument_label: args[0].span,
map_label: arg_ty.default_span(cx.tcx),
suggestion: path.ident.span,
replace: "for_each".to_string(),
},
)
}
}
}
}
}
}
}
fn is_impl_slice(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
if let Some(method_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id) {
if let Some(impl_id) = cx.tcx.impl_of_method(method_id) {
return cx.tcx.type_of(impl_id).skip_binder().is_slice();
}
}
false
}
fn is_unit_type(ty: Ty<'_>) -> bool {
ty.is_unit() || ty.is_never()
}
fn is_diagnostic_name(cx: &LateContext<'_>, id: HirId, name: &str) -> bool {
if let Some(def_id) = cx.typeck_results().type_dependent_def_id(id) {
if let Some(item) = cx.tcx.get_diagnostic_name(def_id) {
if item.as_str() == name {
return true;
}
}
}
false
}
|
