1 use clippy_utils::diagnostics::span_lint_and_sugg;
2 use clippy_utils::{higher, peel_blocks_with_stmt, SpanlessEq};
3 use if_chain::if_chain;
4 use rustc_ast::ast::LitKind;
5 use rustc_errors::Applicability;
6 use rustc_hir::{BinOpKind, Expr, ExprKind, QPath};
7 use rustc_lint::{LateContext, LateLintPass};
8 use rustc_session::{declare_lint_pass, declare_tool_lint};
10 declare_clippy_lint! {
12 /// Checks for implicit saturating subtraction.
14 /// ### Why is this bad?
15 /// Simplicity and readability. Instead we can easily use an builtin function.
19 /// let end: u32 = 10;
20 /// let start: u32 = 5;
22 /// let mut i: u32 = end - start;
30 /// i = i.saturating_sub(1);
32 #[clippy::version = "1.44.0"]
33 pub IMPLICIT_SATURATING_SUB,
35 "Perform saturating subtraction instead of implicitly checking lower bound of data type"
38 declare_lint_pass!(ImplicitSaturatingSub => [IMPLICIT_SATURATING_SUB]);
40 impl<'tcx> LateLintPass<'tcx> for ImplicitSaturatingSub {
41 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
42 if expr.span.from_expansion() {
46 if let Some(higher::If { cond, then, r#else: None }) = higher::If::hir(expr);
48 // Check if the conditional expression is a binary operation
49 if let ExprKind::Binary(ref cond_op, cond_left, cond_right) = cond.kind;
51 // Ensure that the binary operator is >, != and <
52 if BinOpKind::Ne == cond_op.node || BinOpKind::Gt == cond_op.node || BinOpKind::Lt == cond_op.node;
54 // Check if assign operation is done
55 if let Some(target) = subtracts_one(cx, then);
57 // Extracting out the variable name
58 if let ExprKind::Path(QPath::Resolved(_, ares_path)) = target.kind;
61 // Handle symmetric conditions in the if statement
62 let (cond_var, cond_num_val) = if SpanlessEq::new(cx).eq_expr(cond_left, target) {
63 if BinOpKind::Gt == cond_op.node || BinOpKind::Ne == cond_op.node {
64 (cond_left, cond_right)
68 } else if SpanlessEq::new(cx).eq_expr(cond_right, target) {
69 if BinOpKind::Lt == cond_op.node || BinOpKind::Ne == cond_op.node {
70 (cond_right, cond_left)
78 // Check if the variable in the condition statement is an integer
79 if !cx.typeck_results().expr_ty(cond_var).is_integral() {
83 // Get the variable name
84 let var_name = ares_path.segments[0].ident.name.as_str();
85 match cond_num_val.kind {
86 ExprKind::Lit(ref cond_lit) => {
87 // Check if the constant is zero
88 if let LitKind::Int(0, _) = cond_lit.node {
89 if cx.typeck_results().expr_ty(cond_left).is_signed() {
91 print_lint_and_sugg(cx, var_name, expr);
95 ExprKind::Path(QPath::TypeRelative(_, name)) => {
97 if name.ident.as_str() == "MIN";
98 if let Some(const_id) = cx.typeck_results().type_dependent_def_id(cond_num_val.hir_id);
99 if let Some(impl_id) = cx.tcx.impl_of_method(const_id);
100 if let None = cx.tcx.impl_trait_ref(impl_id); // An inherent impl
101 if cx.tcx.type_of(impl_id).is_integral();
103 print_lint_and_sugg(cx, var_name, expr)
107 ExprKind::Call(func, []) => {
109 if let ExprKind::Path(QPath::TypeRelative(_, name)) = func.kind;
110 if name.ident.as_str() == "min_value";
111 if let Some(func_id) = cx.typeck_results().type_dependent_def_id(func.hir_id);
112 if let Some(impl_id) = cx.tcx.impl_of_method(func_id);
113 if let None = cx.tcx.impl_trait_ref(impl_id); // An inherent impl
114 if cx.tcx.type_of(impl_id).is_integral();
116 print_lint_and_sugg(cx, var_name, expr)
127 fn subtracts_one<'a>(cx: &LateContext<'_>, expr: &'a Expr<'a>) -> Option<&'a Expr<'a>> {
128 match peel_blocks_with_stmt(expr).kind {
129 ExprKind::AssignOp(ref op1, target, value) => {
131 if BinOpKind::Sub == op1.node;
132 // Check if literal being subtracted is one
133 if let ExprKind::Lit(ref lit1) = value.kind;
134 if let LitKind::Int(1, _) = lit1.node;
142 ExprKind::Assign(target, value, _) => {
144 if let ExprKind::Binary(ref op1, left1, right1) = value.kind;
145 if BinOpKind::Sub == op1.node;
147 if SpanlessEq::new(cx).eq_expr(left1, target);
149 if let ExprKind::Lit(ref lit1) = right1.kind;
150 if let LitKind::Int(1, _) = lit1.node;
162 fn print_lint_and_sugg(cx: &LateContext<'_>, var_name: &str, expr: &Expr<'_>) {
165 IMPLICIT_SATURATING_SUB,
167 "implicitly performing saturating subtraction",
169 format!("{} = {}.saturating_sub({});", var_name, var_name, '1'),
170 Applicability::MachineApplicable,