1 use crate::utils::{in_macro, match_qpath, SpanlessEq};
2 use clippy_utils::diagnostics::span_lint_and_sugg;
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, StmtKind};
7 use rustc_lint::{LateContext, LateLintPass};
8 use rustc_session::{declare_lint_pass, declare_tool_lint};
10 declare_clippy_lint! {
11 /// **What it does:** Checks for implicit saturating subtraction.
13 /// **Why is this bad?** Simplicity and readability. Instead we can easily use an builtin function.
15 /// **Known problems:** None.
20 /// let end: u32 = 10;
21 /// let start: u32 = 5;
23 /// let mut i: u32 = end - start;
31 /// i = i.saturating_sub(1);
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 in_macro(expr.span) {
46 if let ExprKind::If(cond, then, None) = &expr.kind;
48 // Check if the conditional expression is a binary operation
49 if let ExprKind::Binary(ref cond_op, ref cond_left, ref 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 the true condition block has only one statement
55 if let ExprKind::Block(ref block, _) = then.kind;
56 if block.stmts.len() == 1 && block.expr.is_none();
58 // Check if assign operation is done
59 if let StmtKind::Semi(ref e) = block.stmts[0].kind;
60 if let Some(target) = subtracts_one(cx, e);
62 // Extracting out the variable name
63 if let ExprKind::Path(QPath::Resolved(_, ref ares_path)) = target.kind;
66 // Handle symmetric conditions in the if statement
67 let (cond_var, cond_num_val) = if SpanlessEq::new(cx).eq_expr(cond_left, target) {
68 if BinOpKind::Gt == cond_op.node || BinOpKind::Ne == cond_op.node {
69 (cond_left, cond_right)
73 } else if SpanlessEq::new(cx).eq_expr(cond_right, target) {
74 if BinOpKind::Lt == cond_op.node || BinOpKind::Ne == cond_op.node {
75 (cond_right, cond_left)
83 // Check if the variable in the condition statement is an integer
84 if !cx.typeck_results().expr_ty(cond_var).is_integral() {
88 // Get the variable name
89 let var_name = ares_path.segments[0].ident.name.as_str();
90 const INT_TYPES: [&str; 5] = ["i8", "i16", "i32", "i64", "i128"];
92 match cond_num_val.kind {
93 ExprKind::Lit(ref cond_lit) => {
94 // Check if the constant is zero
95 if let LitKind::Int(0, _) = cond_lit.node {
96 if cx.typeck_results().expr_ty(cond_left).is_signed() {
98 print_lint_and_sugg(cx, &var_name, expr);
102 ExprKind::Path(ref cond_num_path) => {
103 if INT_TYPES.iter().any(|int_type| match_qpath(cond_num_path, &[int_type, "MIN"])) {
104 print_lint_and_sugg(cx, &var_name, expr);
107 ExprKind::Call(ref func, _) => {
108 if let ExprKind::Path(ref cond_num_path) = func.kind {
109 if INT_TYPES.iter().any(|int_type| match_qpath(cond_num_path, &[int_type, "min_value"])) {
110 print_lint_and_sugg(cx, &var_name, expr);
121 fn subtracts_one<'a>(cx: &LateContext<'_>, expr: &Expr<'a>) -> Option<&'a Expr<'a>> {
123 ExprKind::AssignOp(ref op1, ref target, ref value) => {
125 if BinOpKind::Sub == op1.node;
126 // Check if literal being subtracted is one
127 if let ExprKind::Lit(ref lit1) = value.kind;
128 if let LitKind::Int(1, _) = lit1.node;
136 ExprKind::Assign(ref target, ref value, _) => {
138 if let ExprKind::Binary(ref op1, ref left1, ref right1) = value.kind;
139 if BinOpKind::Sub == op1.node;
141 if SpanlessEq::new(cx).eq_expr(left1, target);
143 if let ExprKind::Lit(ref lit1) = right1.kind;
144 if let LitKind::Int(1, _) = lit1.node;
156 fn print_lint_and_sugg(cx: &LateContext<'_>, var_name: &str, expr: &Expr<'_>) {
159 IMPLICIT_SATURATING_SUB,
161 "implicitly performing saturating subtraction",
163 format!("{} = {}.saturating_sub({});", var_name, var_name, '1'),
164 Applicability::MachineApplicable,