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use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::numeric_literal::NumericLiteral;
use clippy_utils::source::snippet_opt;
use clippy_utils::{get_parent_expr, path_to_local};
use if_chain::if_chain;
use rustc_ast::{LitFloatType, LitIntType, LitKind};
use rustc_errors::Applicability;
use rustc_hir::def::Res;
use rustc_hir::{Expr, ExprKind, Lit, QPath, TyKind, UnOp};
use rustc_lint::{LateContext, LintContext};
use rustc_middle::lint::in_external_macro;
use rustc_middle::ty::{self, FloatTy, InferTy, Ty};
use super::UNNECESSARY_CAST;
pub(super) fn check<'tcx>(
cx: &LateContext<'tcx>,
expr: &Expr<'tcx>,
cast_expr: &Expr<'tcx>,
cast_from: Ty<'tcx>,
cast_to: Ty<'tcx>,
) -> bool {
// skip non-primitive type cast
if_chain! {
if let ExprKind::Cast(_, cast_to) = expr.kind;
if let TyKind::Path(QPath::Resolved(_, path)) = &cast_to.kind;
if let Res::PrimTy(_) = path.res;
then {}
else {
return false
}
}
let cast_str = snippet_opt(cx, cast_expr.span).unwrap_or_default();
if let Some(lit) = get_numeric_literal(cast_expr) {
let literal_str = &cast_str;
if_chain! {
if let LitKind::Int(n, _) = lit.node;
if let Some(src) = snippet_opt(cx, cast_expr.span);
if cast_to.is_floating_point();
if let Some(num_lit) = NumericLiteral::from_lit_kind(&src, &lit.node);
let from_nbits = 128 - n.leading_zeros();
let to_nbits = fp_ty_mantissa_nbits(cast_to);
if from_nbits != 0 && to_nbits != 0 && from_nbits <= to_nbits && num_lit.is_decimal();
then {
lint_unnecessary_cast(cx, expr, num_lit.integer, cast_from, cast_to);
return true
}
}
match lit.node {
LitKind::Int(_, LitIntType::Unsuffixed) if cast_to.is_integral() => {
lint_unnecessary_cast(cx, expr, literal_str, cast_from, cast_to);
return false;
},
LitKind::Float(_, LitFloatType::Unsuffixed) if cast_to.is_floating_point() => {
lint_unnecessary_cast(cx, expr, literal_str, cast_from, cast_to);
return false;
},
LitKind::Int(_, LitIntType::Signed(_) | LitIntType::Unsigned(_))
| LitKind::Float(_, LitFloatType::Suffixed(_))
if cast_from.kind() == cast_to.kind() =>
{
if let Some(src) = snippet_opt(cx, cast_expr.span) {
if let Some(num_lit) = NumericLiteral::from_lit_kind(&src, &lit.node) {
lint_unnecessary_cast(cx, expr, num_lit.integer, cast_from, cast_to);
return true;
}
}
},
_ => {},
}
}
if cast_from.kind() == cast_to.kind() && !in_external_macro(cx.sess(), expr.span) {
if let Some(id) = path_to_local(cast_expr)
&& let Some(span) = cx.tcx.hir().opt_span(id)
&& span.ctxt() != cast_expr.span.ctxt()
{
// Binding context is different than the identifiers context.
// Weird macro wizardry could be involved here.
return false;
}
span_lint_and_sugg(
cx,
UNNECESSARY_CAST,
expr.span,
&format!("casting to the same type is unnecessary (`{cast_from}` -> `{cast_to}`)"),
"try",
if get_parent_expr(cx, expr).map_or(false, |e| matches!(e.kind, ExprKind::AddrOf(..))) {
format!("{{ {cast_str} }}")
} else {
cast_str
},
Applicability::MachineApplicable,
);
return true;
}
false
}
fn lint_unnecessary_cast(
cx: &LateContext<'_>,
expr: &Expr<'_>,
raw_literal_str: &str,
cast_from: Ty<'_>,
cast_to: Ty<'_>,
) {
let literal_kind_name = if cast_from.is_integral() { "integer" } else { "float" };
// first we remove all matches so `-(1)` become `-1`, and remove trailing dots, so `1.` become `1`
let literal_str = raw_literal_str
.replace(['(', ')'], "")
.trim_end_matches('.')
.to_string();
// we know need to check if the parent is a method call, to add parenthesis accordingly (eg:
// (-1).foo() instead of -1.foo())
let sugg = if let Some(parent_expr) = get_parent_expr(cx, expr)
&& let ExprKind::MethodCall(..) = parent_expr.kind
&& literal_str.starts_with('-')
{
format!("({literal_str}_{cast_to})")
} else {
format!("{literal_str}_{cast_to}")
};
span_lint_and_sugg(
cx,
UNNECESSARY_CAST,
expr.span,
&format!("casting {literal_kind_name} literal to `{cast_to}` is unnecessary"),
"try",
sugg,
Applicability::MachineApplicable,
);
}
fn get_numeric_literal<'e>(expr: &'e Expr<'e>) -> Option<&'e Lit> {
match expr.kind {
ExprKind::Lit(lit) => Some(lit),
ExprKind::Unary(UnOp::Neg, e) => {
if let ExprKind::Lit(lit) = e.kind {
Some(lit)
} else {
None
}
},
_ => None,
}
}
/// Returns the mantissa bits wide of a fp type.
/// Will return 0 if the type is not a fp
fn fp_ty_mantissa_nbits(typ: Ty<'_>) -> u32 {
match typ.kind() {
ty::Float(FloatTy::F32) => 23,
ty::Float(FloatTy::F64) | ty::Infer(InferTy::FloatVar(_)) => 52,
_ => 0,
}
}
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