| use clippy_utils::diagnostics::span_lint_and_sugg; |
| use clippy_utils::{higher, is_integer_literal, peel_blocks_with_stmt, SpanlessEq}; |
| use rustc_ast::ast::LitKind; |
| use rustc_data_structures::packed::Pu128; |
| use rustc_errors::Applicability; |
| use rustc_hir::{BinOpKind, Expr, ExprKind, QPath}; |
| use rustc_lint::{LateContext, LateLintPass}; |
| use rustc_session::declare_lint_pass; |
| |
| declare_clippy_lint! { |
| /// ### What it does |
| /// Checks for implicit saturating subtraction. |
| /// |
| /// ### Why is this bad? |
| /// Simplicity and readability. Instead we can easily use an builtin function. |
| /// |
| /// ### Example |
| /// ```no_run |
| /// # let end: u32 = 10; |
| /// # let start: u32 = 5; |
| /// let mut i: u32 = end - start; |
| /// |
| /// if i != 0 { |
| /// i -= 1; |
| /// } |
| /// ``` |
| /// |
| /// Use instead: |
| /// ```no_run |
| /// # let end: u32 = 10; |
| /// # let start: u32 = 5; |
| /// let mut i: u32 = end - start; |
| /// |
| /// i = i.saturating_sub(1); |
| /// ``` |
| #[clippy::version = "1.44.0"] |
| pub IMPLICIT_SATURATING_SUB, |
| style, |
| "Perform saturating subtraction instead of implicitly checking lower bound of data type" |
| } |
| |
| declare_lint_pass!(ImplicitSaturatingSub => [IMPLICIT_SATURATING_SUB]); |
| |
| impl<'tcx> LateLintPass<'tcx> for ImplicitSaturatingSub { |
| fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) { |
| if expr.span.from_expansion() { |
| return; |
| } |
| if let Some(higher::If { cond, then, r#else: None }) = higher::If::hir(expr) |
| |
| // Check if the conditional expression is a binary operation |
| && let ExprKind::Binary(ref cond_op, cond_left, cond_right) = cond.kind |
| |
| // Ensure that the binary operator is >, !=, or < |
| && (BinOpKind::Ne == cond_op.node || BinOpKind::Gt == cond_op.node || BinOpKind::Lt == cond_op.node) |
| |
| // Check if assign operation is done |
| && let Some(target) = subtracts_one(cx, then) |
| |
| // Extracting out the variable name |
| && let ExprKind::Path(QPath::Resolved(_, ares_path)) = target.kind |
| { |
| // Handle symmetric conditions in the if statement |
| let (cond_var, cond_num_val) = if SpanlessEq::new(cx).eq_expr(cond_left, target) { |
| if BinOpKind::Gt == cond_op.node || BinOpKind::Ne == cond_op.node { |
| (cond_left, cond_right) |
| } else { |
| return; |
| } |
| } else if SpanlessEq::new(cx).eq_expr(cond_right, target) { |
| if BinOpKind::Lt == cond_op.node || BinOpKind::Ne == cond_op.node { |
| (cond_right, cond_left) |
| } else { |
| return; |
| } |
| } else { |
| return; |
| }; |
| |
| // Check if the variable in the condition statement is an integer |
| if !cx.typeck_results().expr_ty(cond_var).is_integral() { |
| return; |
| } |
| |
| // Get the variable name |
| let var_name = ares_path.segments[0].ident.name.as_str(); |
| match cond_num_val.kind { |
| ExprKind::Lit(cond_lit) => { |
| // Check if the constant is zero |
| if let LitKind::Int(Pu128(0), _) = cond_lit.node { |
| if cx.typeck_results().expr_ty(cond_left).is_signed() { |
| } else { |
| print_lint_and_sugg(cx, var_name, expr); |
| }; |
| } |
| }, |
| ExprKind::Path(QPath::TypeRelative(_, name)) => { |
| if name.ident.as_str() == "MIN" |
| && let Some(const_id) = cx.typeck_results().type_dependent_def_id(cond_num_val.hir_id) |
| && let Some(impl_id) = cx.tcx.impl_of_method(const_id) |
| && let None = cx.tcx.impl_trait_ref(impl_id) // An inherent impl |
| && cx.tcx.type_of(impl_id).instantiate_identity().is_integral() |
| { |
| print_lint_and_sugg(cx, var_name, expr); |
| } |
| }, |
| ExprKind::Call(func, []) => { |
| if let ExprKind::Path(QPath::TypeRelative(_, name)) = func.kind |
| && name.ident.as_str() == "min_value" |
| && let Some(func_id) = cx.typeck_results().type_dependent_def_id(func.hir_id) |
| && let Some(impl_id) = cx.tcx.impl_of_method(func_id) |
| && let None = cx.tcx.impl_trait_ref(impl_id) // An inherent impl |
| && cx.tcx.type_of(impl_id).instantiate_identity().is_integral() |
| { |
| print_lint_and_sugg(cx, var_name, expr); |
| } |
| }, |
| _ => (), |
| } |
| } |
| } |
| } |
| |
| fn subtracts_one<'a>(cx: &LateContext<'_>, expr: &'a Expr<'a>) -> Option<&'a Expr<'a>> { |
| match peel_blocks_with_stmt(expr).kind { |
| ExprKind::AssignOp(ref op1, target, value) => { |
| // Check if literal being subtracted is one |
| (BinOpKind::Sub == op1.node && is_integer_literal(value, 1)).then_some(target) |
| }, |
| ExprKind::Assign(target, value, _) => { |
| if let ExprKind::Binary(ref op1, left1, right1) = value.kind |
| && BinOpKind::Sub == op1.node |
| && SpanlessEq::new(cx).eq_expr(left1, target) |
| && is_integer_literal(right1, 1) |
| { |
| Some(target) |
| } else { |
| None |
| } |
| }, |
| _ => None, |
| } |
| } |
| |
| fn print_lint_and_sugg(cx: &LateContext<'_>, var_name: &str, expr: &Expr<'_>) { |
| span_lint_and_sugg( |
| cx, |
| IMPLICIT_SATURATING_SUB, |
| expr.span, |
| "implicitly performing saturating subtraction", |
| "try", |
| format!("{var_name} = {var_name}.saturating_sub({});", '1'), |
| Applicability::MachineApplicable, |
| ); |
| } |