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use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::{higher, is_integer_literal, peel_blocks_with_stmt, SpanlessEq};
use if_chain::if_chain;
use rustc_ast::ast::LitKind;
use rustc_errors::Applicability;
use rustc_hir::{BinOpKind, Expr, ExprKind, QPath};
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::{declare_lint_pass, declare_tool_lint};
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
/// ```rust
/// # let end: u32 = 10;
/// # let start: u32 = 5;
/// let mut i: u32 = end - start;
///
/// if i != 0 {
/// i -= 1;
/// }
/// ```
///
/// Use instead:
/// ```rust
/// # 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_chain! {
if let Some(higher::If { cond, then, r#else: None }) = higher::If::hir(expr);
// Check if the conditional expression is a binary operation
if let ExprKind::Binary(ref cond_op, cond_left, cond_right) = cond.kind;
// Ensure that the binary operator is >, !=, or <
if BinOpKind::Ne == cond_op.node || BinOpKind::Gt == cond_op.node || BinOpKind::Lt == cond_op.node;
// Check if assign operation is done
if let Some(target) = subtracts_one(cx, then);
// Extracting out the variable name
if let ExprKind::Path(QPath::Resolved(_, ares_path)) = target.kind;
then {
// 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(ref cond_lit) => {
// Check if the constant is zero
if let LitKind::Int(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_chain! {
if name.ident.as_str() == "MIN";
if let Some(const_id) = cx.typeck_results().type_dependent_def_id(cond_num_val.hir_id);
if let Some(impl_id) = cx.tcx.impl_of_method(const_id);
if let None = cx.tcx.impl_trait_ref(impl_id); // An inherent impl
if cx.tcx.type_of(impl_id).subst_identity().is_integral();
then {
print_lint_and_sugg(cx, var_name, expr)
}
}
},
ExprKind::Call(func, []) => {
if_chain! {
if let ExprKind::Path(QPath::TypeRelative(_, name)) = func.kind;
if name.ident.as_str() == "min_value";
if let Some(func_id) = cx.typeck_results().type_dependent_def_id(func.hir_id);
if let Some(impl_id) = cx.tcx.impl_of_method(func_id);
if let None = cx.tcx.impl_trait_ref(impl_id); // An inherent impl
if cx.tcx.type_of(impl_id).subst_identity().is_integral();
then {
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_chain! {
if let ExprKind::Binary(ref op1, left1, right1) = value.kind;
if BinOpKind::Sub == op1.node;
if SpanlessEq::new(cx).eq_expr(left1, target);
if is_integer_literal(right1, 1);
then {
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,
);
}
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