rustc_lint/
map_unit_fn.rs1use rustc_hir::{Expr, ExprKind, HirId, Stmt, StmtKind};
2use rustc_middle::ty::{self, Ty};
3use rustc_session::{declare_lint, declare_lint_pass};
4
5use crate::lints::MappingToUnit;
6use crate::{LateContext, LateLintPass, LintContext};
7
8declare_lint! {
9 pub MAP_UNIT_FN,
34 Warn,
35 "`Iterator::map` call that discard the iterator's values"
36}
37
38declare_lint_pass!(MapUnitFn => [MAP_UNIT_FN]);
39
40impl<'tcx> LateLintPass<'tcx> for MapUnitFn {
41 fn check_stmt(&mut self, cx: &LateContext<'tcx>, stmt: &Stmt<'_>) {
42 if stmt.span.from_expansion() {
43 return;
44 }
45
46 if let StmtKind::Semi(expr) = stmt.kind {
47 if let ExprKind::MethodCall(path, receiver, args, span) = expr.kind {
48 if path.ident.name.as_str() == "map" {
49 if receiver.span.from_expansion()
50 || args.iter().any(|e| e.span.from_expansion())
51 || !is_impl_slice(cx, receiver)
52 || !is_diagnostic_name(cx, expr.hir_id, "IteratorMap")
53 {
54 return;
55 }
56 let arg_ty = cx.typeck_results().expr_ty(&args[0]);
57 let default_span = args[0].span;
58 if let ty::FnDef(id, _) = arg_ty.kind() {
59 let fn_ty = cx.tcx.fn_sig(id).skip_binder();
60 let ret_ty = fn_ty.output().skip_binder();
61 if is_unit_type(ret_ty) {
62 cx.emit_span_lint(
63 MAP_UNIT_FN,
64 span,
65 MappingToUnit {
66 function_label: cx
67 .tcx
68 .span_of_impl(*id)
69 .unwrap_or(default_span),
70 argument_label: args[0].span,
71 map_label: span,
72 suggestion: path.ident.span,
73 replace: "for_each".to_string(),
74 },
75 )
76 }
77 } else if let ty::Closure(id, subs) = arg_ty.kind() {
78 let cl_ty = subs.as_closure().sig();
79 let ret_ty = cl_ty.output().skip_binder();
80 if is_unit_type(ret_ty) {
81 cx.emit_span_lint(
82 MAP_UNIT_FN,
83 span,
84 MappingToUnit {
85 function_label: cx
86 .tcx
87 .span_of_impl(*id)
88 .unwrap_or(default_span),
89 argument_label: args[0].span,
90 map_label: span,
91 suggestion: path.ident.span,
92 replace: "for_each".to_string(),
93 },
94 )
95 }
96 }
97 }
98 }
99 }
100 }
101}
102
103fn is_impl_slice(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
104 if let Some(method_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id) {
105 if let Some(impl_id) = cx.tcx.impl_of_method(method_id) {
106 return cx.tcx.type_of(impl_id).skip_binder().is_slice();
107 }
108 }
109 false
110}
111
112fn is_unit_type(ty: Ty<'_>) -> bool {
113 ty.is_unit() || ty.is_never()
114}
115
116fn is_diagnostic_name(cx: &LateContext<'_>, id: HirId, name: &str) -> bool {
117 if let Some(def_id) = cx.typeck_results().type_dependent_def_id(id) {
118 if let Some(item) = cx.tcx.get_diagnostic_name(def_id) {
119 if item.as_str() == name {
120 return true;
121 }
122 }
123 }
124 false
125}