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[rustc.git] / src / tools / clippy / clippy_lints / src / int_plus_one.rs
1 //! lint on blocks unnecessarily using >= with a + 1 or - 1
2
3 use clippy_utils::diagnostics::span_lint_and_sugg;
4 use clippy_utils::source::snippet_opt;
5 use rustc_ast::ast::{BinOpKind, Expr, ExprKind, LitKind};
6 use rustc_ast::token;
7 use rustc_errors::Applicability;
8 use rustc_lint::{EarlyContext, EarlyLintPass};
9 use rustc_session::{declare_lint_pass, declare_tool_lint};
10
11 declare_clippy_lint! {
12 /// ### What it does
13 /// Checks for usage of `x >= y + 1` or `x - 1 >= y` (and `<=`) in a block
14 ///
15 /// ### Why is this bad?
16 /// Readability -- better to use `> y` instead of `>= y + 1`.
17 ///
18 /// ### Example
19 /// ```no_run
20 /// # let x = 1;
21 /// # let y = 1;
22 /// if x >= y + 1 {}
23 /// ```
24 ///
25 /// Use instead:
26 /// ```no_run
27 /// # let x = 1;
28 /// # let y = 1;
29 /// if x > y {}
30 /// ```
31 #[clippy::version = "pre 1.29.0"]
32 pub INT_PLUS_ONE,
33 complexity,
34 "instead of using `x >= y + 1`, use `x > y`"
35 }
36
37 declare_lint_pass!(IntPlusOne => [INT_PLUS_ONE]);
38
39 // cases:
40 // BinOpKind::Ge
41 // x >= y + 1
42 // x - 1 >= y
43 //
44 // BinOpKind::Le
45 // x + 1 <= y
46 // x <= y - 1
47
48 #[derive(Copy, Clone)]
49 enum Side {
50 Lhs,
51 Rhs,
52 }
53
54 impl IntPlusOne {
55 #[expect(clippy::cast_sign_loss)]
56 fn check_lit(token_lit: token::Lit, target_value: i128) -> bool {
57 if let Ok(LitKind::Int(value, ..)) = LitKind::from_token_lit(token_lit) {
58 return value == (target_value as u128);
59 }
60 false
61 }
62
63 fn check_binop(cx: &EarlyContext<'_>, binop: BinOpKind, lhs: &Expr, rhs: &Expr) -> Option<String> {
64 match (binop, &lhs.kind, &rhs.kind) {
65 // case where `x - 1 >= ...` or `-1 + x >= ...`
66 (BinOpKind::Ge, ExprKind::Binary(lhskind, lhslhs, lhsrhs), _) => {
67 match (lhskind.node, &lhslhs.kind, &lhsrhs.kind) {
68 // `-1 + x`
69 (BinOpKind::Add, ExprKind::Lit(lit), _) if Self::check_lit(*lit, -1) => {
70 Self::generate_recommendation(cx, binop, lhsrhs, rhs, Side::Lhs)
71 },
72 // `x - 1`
73 (BinOpKind::Sub, _, ExprKind::Lit(lit)) if Self::check_lit(*lit, 1) => {
74 Self::generate_recommendation(cx, binop, lhslhs, rhs, Side::Lhs)
75 },
76 _ => None,
77 }
78 },
79 // case where `... >= y + 1` or `... >= 1 + y`
80 (BinOpKind::Ge, _, ExprKind::Binary(rhskind, rhslhs, rhsrhs)) if rhskind.node == BinOpKind::Add => {
81 match (&rhslhs.kind, &rhsrhs.kind) {
82 // `y + 1` and `1 + y`
83 (ExprKind::Lit(lit), _) if Self::check_lit(*lit, 1) => {
84 Self::generate_recommendation(cx, binop, rhsrhs, lhs, Side::Rhs)
85 },
86 (_, ExprKind::Lit(lit)) if Self::check_lit(*lit, 1) => {
87 Self::generate_recommendation(cx, binop, rhslhs, lhs, Side::Rhs)
88 },
89 _ => None,
90 }
91 },
92 // case where `x + 1 <= ...` or `1 + x <= ...`
93 (BinOpKind::Le, ExprKind::Binary(lhskind, lhslhs, lhsrhs), _) if lhskind.node == BinOpKind::Add => {
94 match (&lhslhs.kind, &lhsrhs.kind) {
95 // `1 + x` and `x + 1`
96 (ExprKind::Lit(lit), _) if Self::check_lit(*lit, 1) => {
97 Self::generate_recommendation(cx, binop, lhsrhs, rhs, Side::Lhs)
98 },
99 (_, ExprKind::Lit(lit)) if Self::check_lit(*lit, 1) => {
100 Self::generate_recommendation(cx, binop, lhslhs, rhs, Side::Lhs)
101 },
102 _ => None,
103 }
104 },
105 // case where `... >= y - 1` or `... >= -1 + y`
106 (BinOpKind::Le, _, ExprKind::Binary(rhskind, rhslhs, rhsrhs)) => {
107 match (rhskind.node, &rhslhs.kind, &rhsrhs.kind) {
108 // `-1 + y`
109 (BinOpKind::Add, ExprKind::Lit(lit), _) if Self::check_lit(*lit, -1) => {
110 Self::generate_recommendation(cx, binop, rhsrhs, lhs, Side::Rhs)
111 },
112 // `y - 1`
113 (BinOpKind::Sub, _, ExprKind::Lit(lit)) if Self::check_lit(*lit, 1) => {
114 Self::generate_recommendation(cx, binop, rhslhs, lhs, Side::Rhs)
115 },
116 _ => None,
117 }
118 },
119 _ => None,
120 }
121 }
122
123 fn generate_recommendation(
124 cx: &EarlyContext<'_>,
125 binop: BinOpKind,
126 node: &Expr,
127 other_side: &Expr,
128 side: Side,
129 ) -> Option<String> {
130 let binop_string = match binop {
131 BinOpKind::Ge => ">",
132 BinOpKind::Le => "<",
133 _ => return None,
134 };
135 if let Some(snippet) = snippet_opt(cx, node.span) {
136 if let Some(other_side_snippet) = snippet_opt(cx, other_side.span) {
137 let rec = match side {
138 Side::Lhs => Some(format!("{snippet} {binop_string} {other_side_snippet}")),
139 Side::Rhs => Some(format!("{other_side_snippet} {binop_string} {snippet}")),
140 };
141 return rec;
142 }
143 }
144 None
145 }
146
147 fn emit_warning(cx: &EarlyContext<'_>, block: &Expr, recommendation: String) {
148 span_lint_and_sugg(
149 cx,
150 INT_PLUS_ONE,
151 block.span,
152 "unnecessary `>= y + 1` or `x - 1 >=`",
153 "change it to",
154 recommendation,
155 Applicability::MachineApplicable, // snippet
156 );
157 }
158 }
159
160 impl EarlyLintPass for IntPlusOne {
161 fn check_expr(&mut self, cx: &EarlyContext<'_>, item: &Expr) {
162 if let ExprKind::Binary(ref kind, ref lhs, ref rhs) = item.kind {
163 if let Some(rec) = Self::check_binop(cx, kind.node, lhs, rhs) {
164 Self::emit_warning(cx, item, rec);
165 }
166 }
167 }
168 }