2021-03-25 18:29:11 +00:00
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use clippy_utils::diagnostics::span_lint_and_sugg;
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2021-12-17 12:40:22 +00:00
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use clippy_utils::{higher, peel_blocks_with_stmt, SpanlessEq};
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2020-04-06 18:07:57 +00:00
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use if_chain::if_chain;
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use rustc_ast::ast::LitKind;
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use rustc_errors::Applicability;
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2022-03-18 12:33:40 +00:00
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use rustc_hir::{BinOpKind, Expr, ExprKind, QPath};
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2020-04-06 18:07:57 +00:00
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_session::{declare_lint_pass, declare_tool_lint};
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declare_clippy_lint! {
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2021-07-29 10:16:06 +00:00
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/// ### What it does
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/// Checks for implicit saturating subtraction.
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2020-04-06 18:07:57 +00:00
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///
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2021-07-29 10:16:06 +00:00
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/// ### Why is this bad?
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/// Simplicity and readability. Instead we can easily use an builtin function.
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2020-04-06 18:07:57 +00:00
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///
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2021-07-29 10:16:06 +00:00
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/// ### Example
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/// ```rust
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2020-04-06 18:10:41 +00:00
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/// let end: u32 = 10;
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/// let start: u32 = 5;
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///
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/// let mut i: u32 = end - start;
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2020-04-06 18:07:57 +00:00
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///
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/// // Bad
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/// if i != 0 {
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/// i -= 1;
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/// }
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///
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/// // Good
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/// i = i.saturating_sub(1);
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2020-04-06 18:07:57 +00:00
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/// ```
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2021-12-06 11:33:31 +00:00
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#[clippy::version = "1.44.0"]
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pub IMPLICIT_SATURATING_SUB,
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pedantic,
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"Perform saturating subtraction instead of implicitly checking lower bound of data type"
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}
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declare_lint_pass!(ImplicitSaturatingSub => [IMPLICIT_SATURATING_SUB]);
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2020-06-25 20:41:36 +00:00
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impl<'tcx> LateLintPass<'tcx> for ImplicitSaturatingSub {
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fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
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2021-12-06 11:33:31 +00:00
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if expr.span.from_expansion() {
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return;
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}
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if_chain! {
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2021-10-21 11:11:36 +00:00
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if let Some(higher::If { cond, then, r#else: None }) = higher::If::hir(expr);
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2020-04-06 18:10:41 +00:00
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// Check if the conditional expression is a binary operation
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if let ExprKind::Binary(ref cond_op, cond_left, cond_right) = cond.kind;
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// Ensure that the binary operator is >, != and <
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if BinOpKind::Ne == cond_op.node || BinOpKind::Gt == cond_op.node || BinOpKind::Lt == cond_op.node;
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// Check if assign operation is done
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if let Some(target) = subtracts_one(cx, then);
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2020-04-06 18:10:41 +00:00
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// Extracting out the variable name
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if let ExprKind::Path(QPath::Resolved(_, ares_path)) = target.kind;
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then {
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// Handle symmetric conditions in the if statement
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let (cond_var, cond_num_val) = if SpanlessEq::new(cx).eq_expr(cond_left, target) {
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if BinOpKind::Gt == cond_op.node || BinOpKind::Ne == cond_op.node {
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(cond_left, cond_right)
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} else {
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return;
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}
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} else if SpanlessEq::new(cx).eq_expr(cond_right, target) {
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if BinOpKind::Lt == cond_op.node || BinOpKind::Ne == cond_op.node {
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(cond_right, cond_left)
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} else {
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return;
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}
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} else {
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return;
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};
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// Check if the variable in the condition statement is an integer
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if !cx.typeck_results().expr_ty(cond_var).is_integral() {
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return;
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}
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// Get the variable name
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let var_name = ares_path.segments[0].ident.name.as_str();
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match cond_num_val.kind {
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ExprKind::Lit(ref cond_lit) => {
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// Check if the constant is zero
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if let LitKind::Int(0, _) = cond_lit.node {
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if cx.typeck_results().expr_ty(cond_left).is_signed() {
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} else {
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print_lint_and_sugg(cx, var_name, expr);
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};
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}
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},
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ExprKind::Path(QPath::TypeRelative(_, name)) => {
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if_chain! {
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if name.ident.as_str() == "MIN";
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if let Some(const_id) = cx.typeck_results().type_dependent_def_id(cond_num_val.hir_id);
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if let Some(impl_id) = cx.tcx.impl_of_method(const_id);
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if let None = cx.tcx.impl_trait_ref(impl_id); // An inherent impl
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if cx.tcx.type_of(impl_id).is_integral();
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then {
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print_lint_and_sugg(cx, var_name, expr)
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}
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}
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2020-04-06 18:10:41 +00:00
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},
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ExprKind::Call(func, []) => {
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if_chain! {
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if let ExprKind::Path(QPath::TypeRelative(_, name)) = func.kind;
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if name.ident.as_str() == "min_value";
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if let Some(func_id) = cx.typeck_results().type_dependent_def_id(func.hir_id);
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if let Some(impl_id) = cx.tcx.impl_of_method(func_id);
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if let None = cx.tcx.impl_trait_ref(impl_id); // An inherent impl
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if cx.tcx.type_of(impl_id).is_integral();
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then {
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2021-12-30 14:10:43 +00:00
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print_lint_and_sugg(cx, var_name, expr)
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2020-04-06 18:10:41 +00:00
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}
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2021-04-22 09:31:13 +00:00
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}
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2020-04-06 18:10:41 +00:00
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},
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_ => (),
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}
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2020-04-06 18:07:57 +00:00
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}
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}
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}
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}
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2020-04-06 18:10:41 +00:00
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2021-12-17 12:40:22 +00:00
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fn subtracts_one<'a>(cx: &LateContext<'_>, expr: &'a Expr<'a>) -> Option<&'a Expr<'a>> {
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match peel_blocks_with_stmt(expr).kind {
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ExprKind::AssignOp(ref op1, target, value) => {
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2020-04-06 18:10:41 +00:00
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if_chain! {
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if BinOpKind::Sub == op1.node;
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// Check if literal being subtracted is one
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if let ExprKind::Lit(ref lit1) = value.kind;
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if let LitKind::Int(1, _) = lit1.node;
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then {
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Some(target)
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} else {
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None
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}
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}
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},
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ExprKind::Assign(target, value, _) => {
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if_chain! {
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if let ExprKind::Binary(ref op1, left1, right1) = value.kind;
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if BinOpKind::Sub == op1.node;
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if SpanlessEq::new(cx).eq_expr(left1, target);
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if let ExprKind::Lit(ref lit1) = right1.kind;
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if let LitKind::Int(1, _) = lit1.node;
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then {
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Some(target)
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} else {
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None
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}
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}
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},
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_ => None,
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}
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}
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2020-06-25 20:41:36 +00:00
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fn print_lint_and_sugg(cx: &LateContext<'_>, var_name: &str, expr: &Expr<'_>) {
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2020-04-06 18:10:41 +00:00
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span_lint_and_sugg(
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cx,
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IMPLICIT_SATURATING_SUB,
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expr.span,
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2020-08-28 14:10:16 +00:00
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"implicitly performing saturating subtraction",
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2020-04-06 18:10:41 +00:00
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"try",
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2020-08-28 14:10:16 +00:00
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format!("{} = {}.saturating_sub({});", var_name, var_name, '1'),
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2020-04-06 18:10:41 +00:00
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Applicability::MachineApplicable,
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);
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}
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