1 use crate::utils::{higher, in_macro, match_qpath, span_lint_and_sugg, SpanlessEq};
2 use if_chain::if_chain;
3 use rustc_ast::ast::LitKind;
4 use rustc_errors::Applicability;
5 use rustc_hir::{BinOpKind, Expr, ExprKind, QPath, StmtKind};
6 use rustc_lint::{LateContext, LateLintPass};
7 use rustc_session::{declare_lint_pass, declare_tool_lint};
10 /// **What it does:** Checks for implicit saturating subtraction.
12 /// **Why is this bad?** Simplicity and readability. Instead we can easily use an builtin function.
14 /// **Known problems:** None.
19 /// let end: u32 = 10;
20 /// let start: u32 = 5;
22 /// let mut i: u32 = end - start;
31 /// let end: u32 = 10;
32 /// let start: u32 = 5;
34 /// let mut i: u32 = end - start;
37 /// i = i.saturating_sub(1);
39 pub IMPLICIT_SATURATING_SUB,
41 "Perform saturating subtraction instead of implicitly checking lower bound of data type"
44 declare_lint_pass!(ImplicitSaturatingSub => [IMPLICIT_SATURATING_SUB]);
46 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ImplicitSaturatingSub {
47 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'tcx>) {
48 if in_macro(expr.span) {
52 if let Some((ref cond, ref then, None)) = higher::if_block(&expr);
54 // Check if the conditional expression is a binary operation
55 if let ExprKind::Binary(ref cond_op, ref cond_left, ref cond_right) = cond.kind;
57 // Ensure that the binary operator is >, != and <
58 if BinOpKind::Ne == cond_op.node || BinOpKind::Gt == cond_op.node || BinOpKind::Lt == cond_op.node;
60 // Check if the true condition block has only one statement
61 if let ExprKind::Block(ref block, _) = then.kind;
62 if block.stmts.len() == 1 && block.expr.is_none();
64 // Check if assign operation is done
65 if let StmtKind::Semi(ref e) = block.stmts[0].kind;
66 if let Some(target) = subtracts_one(cx, e);
68 // Extracting out the variable name
69 if let ExprKind::Path(ref assign_path) = target.kind;
70 if let QPath::Resolved(_, ref ares_path) = assign_path;
73 // Handle symmetric conditions in the if statement
74 let (cond_var, cond_num_val) = if SpanlessEq::new(cx).eq_expr(cond_left, target) {
75 if BinOpKind::Gt == cond_op.node || BinOpKind::Ne == cond_op.node {
76 (cond_left, cond_right)
80 } else if SpanlessEq::new(cx).eq_expr(cond_right, target) {
81 if BinOpKind::Lt == cond_op.node || BinOpKind::Ne == cond_op.node {
82 (cond_right, cond_left)
90 // Check if the variable in the condition statement is an integer
91 if !cx.tables.expr_ty(cond_var).is_integral() {
95 // Get the variable name
96 let var_name = ares_path.segments[0].ident.name.as_str();
97 const INT_TYPES: [&str; 5] = ["i8", "i16", "i32", "i64", "i128"];
99 match cond_num_val.kind {
100 ExprKind::Lit(ref cond_lit) => {
101 // Check if the constant is zero
102 if let LitKind::Int(0, _) = cond_lit.node {
103 if cx.tables.expr_ty(cond_left).is_signed() {
105 print_lint_and_sugg(cx, &var_name, expr);
109 ExprKind::Path(ref cond_num_path) => {
110 if INT_TYPES.iter().any(|int_type| match_qpath(cond_num_path, &[int_type, "MIN"])) {
111 print_lint_and_sugg(cx, &var_name, expr);
114 ExprKind::Call(ref func, _) => {
115 if let ExprKind::Path(ref cond_num_path) = func.kind {
116 if INT_TYPES.iter().any(|int_type| match_qpath(cond_num_path, &[int_type, "min_value"])) {
117 print_lint_and_sugg(cx, &var_name, expr);
128 fn subtracts_one<'a>(cx: &LateContext<'_, '_>, expr: &Expr<'a>) -> Option<&'a Expr<'a>> {
130 ExprKind::AssignOp(ref op1, ref target, ref value) => {
132 if BinOpKind::Sub == op1.node;
133 // Check if literal being subtracted is one
134 if let ExprKind::Lit(ref lit1) = value.kind;
135 if let LitKind::Int(1, _) = lit1.node;
143 ExprKind::Assign(ref target, ref value, _) => {
145 if let ExprKind::Binary(ref op1, ref left1, ref right1) = value.kind;
146 if BinOpKind::Sub == op1.node;
148 if SpanlessEq::new(cx).eq_expr(left1, target);
150 if let ExprKind::Lit(ref lit1) = right1.kind;
151 if let LitKind::Int(1, _) = lit1.node;
163 fn print_lint_and_sugg(cx: &LateContext<'_, '_>, var_name: &str, expr: &Expr<'_>) {
166 IMPLICIT_SATURATING_SUB,
168 "Implicitly performing saturating subtraction",
170 format!("{} = {}.saturating_sub({});", var_name, var_name, 1.to_string()),
171 Applicability::MachineApplicable,