1 use clippy_utils::diagnostics::span_lint_and_sugg;
2 use clippy_utils::{in_macro, SpanlessEq};
3 use if_chain::if_chain;
4 use rustc_ast::ast::LitKind;
5 use rustc_errors::Applicability;
6 use rustc_hir::{lang_items::LangItem, BinOpKind, Expr, ExprKind, QPath, StmtKind};
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 pub IMPLICIT_SATURATING_SUB,
34 "Perform saturating subtraction instead of implicitly checking lower bound of data type"
37 declare_lint_pass!(ImplicitSaturatingSub => [IMPLICIT_SATURATING_SUB]);
39 impl<'tcx> LateLintPass<'tcx> for ImplicitSaturatingSub {
40 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
41 if in_macro(expr.span) {
45 if let ExprKind::If(cond, then, None) = &expr.kind;
47 // Check if the conditional expression is a binary operation
48 if let ExprKind::Binary(ref cond_op, cond_left, cond_right) = cond.kind;
50 // Ensure that the binary operator is >, != and <
51 if BinOpKind::Ne == cond_op.node || BinOpKind::Gt == cond_op.node || BinOpKind::Lt == cond_op.node;
53 // Check if the true condition block has only one statement
54 if let ExprKind::Block(block, _) = then.kind;
55 if block.stmts.len() == 1 && block.expr.is_none();
57 // Check if assign operation is done
58 if let StmtKind::Semi(e) = block.stmts[0].kind;
59 if let Some(target) = subtracts_one(cx, e);
61 // Extracting out the variable name
62 if let ExprKind::Path(QPath::Resolved(_, ares_path)) = target.kind;
65 // Handle symmetric conditions in the if statement
66 let (cond_var, cond_num_val) = if SpanlessEq::new(cx).eq_expr(cond_left, target) {
67 if BinOpKind::Gt == cond_op.node || BinOpKind::Ne == cond_op.node {
68 (cond_left, cond_right)
72 } else if SpanlessEq::new(cx).eq_expr(cond_right, target) {
73 if BinOpKind::Lt == cond_op.node || BinOpKind::Ne == cond_op.node {
74 (cond_right, cond_left)
82 // Check if the variable in the condition statement is an integer
83 if !cx.typeck_results().expr_ty(cond_var).is_integral() {
87 // Get the variable name
88 let var_name = ares_path.segments[0].ident.name.as_str();
89 const INT_TYPES: [LangItem; 5] = [
97 match cond_num_val.kind {
98 ExprKind::Lit(ref cond_lit) => {
99 // Check if the constant is zero
100 if let LitKind::Int(0, _) = cond_lit.node {
101 if cx.typeck_results().expr_ty(cond_left).is_signed() {
103 print_lint_and_sugg(cx, &var_name, expr);
107 ExprKind::Path(QPath::TypeRelative(_, name)) => {
109 if name.ident.as_str() == "MIN";
110 if let Some(const_id) = cx.typeck_results().type_dependent_def_id(cond_num_val.hir_id);
111 if let Some(impl_id) = cx.tcx.impl_of_method(const_id);
112 let mut int_ids = INT_TYPES.iter().filter_map(|&ty| cx.tcx.lang_items().require(ty).ok());
113 if int_ids.any(|int_id| int_id == impl_id);
115 print_lint_and_sugg(cx, &var_name, expr)
119 ExprKind::Call(func, []) => {
121 if let ExprKind::Path(QPath::TypeRelative(_, name)) = func.kind;
122 if name.ident.as_str() == "min_value";
123 if let Some(func_id) = cx.typeck_results().type_dependent_def_id(func.hir_id);
124 if let Some(impl_id) = cx.tcx.impl_of_method(func_id);
125 let mut int_ids = INT_TYPES.iter().filter_map(|&ty| cx.tcx.lang_items().require(ty).ok());
126 if int_ids.any(|int_id| int_id == impl_id);
128 print_lint_and_sugg(cx, &var_name, expr)
139 fn subtracts_one<'a>(cx: &LateContext<'_>, expr: &Expr<'a>) -> Option<&'a Expr<'a>> {
141 ExprKind::AssignOp(ref op1, target, value) => {
143 if BinOpKind::Sub == op1.node;
144 // Check if literal being subtracted is one
145 if let ExprKind::Lit(ref lit1) = value.kind;
146 if let LitKind::Int(1, _) = lit1.node;
154 ExprKind::Assign(target, value, _) => {
156 if let ExprKind::Binary(ref op1, left1, right1) = value.kind;
157 if BinOpKind::Sub == op1.node;
159 if SpanlessEq::new(cx).eq_expr(left1, target);
161 if let ExprKind::Lit(ref lit1) = right1.kind;
162 if let LitKind::Int(1, _) = lit1.node;
174 fn print_lint_and_sugg(cx: &LateContext<'_>, var_name: &str, expr: &Expr<'_>) {
177 IMPLICIT_SATURATING_SUB,
179 "implicitly performing saturating subtraction",
181 format!("{} = {}.saturating_sub({});", var_name, var_name, '1'),
182 Applicability::MachineApplicable,