rust/clippy_lints/src/manual_slice_size_calculation.rs
2023-07-14 13:27:35 +01:00

104 lines
3.6 KiB
Rust

use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::source::snippet_with_context;
use clippy_utils::{expr_or_init, in_constant, std_or_core};
use rustc_errors::Applicability;
use rustc_hir::{BinOpKind, Expr, ExprKind};
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::ty;
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::symbol::sym;
declare_clippy_lint! {
/// ### What it does
/// When `a` is `&[T]`, detect `a.len() * size_of::<T>()` and suggest `size_of_val(a)`
/// instead.
///
/// ### Why is this better?
/// * Shorter to write
/// * Removes the need for the human and the compiler to worry about overflow in the
/// multiplication
/// * Potentially faster at runtime as rust emits special no-wrapping flags when it
/// calculates the byte length
/// * Less turbofishing
///
/// ### Example
/// ```rust
/// # let data : &[i32] = &[1, 2, 3];
/// let newlen = data.len() * std::mem::size_of::<i32>();
/// ```
/// Use instead:
/// ```rust
/// # let data : &[i32] = &[1, 2, 3];
/// let newlen = std::mem::size_of_val(data);
/// ```
#[clippy::version = "1.70.0"]
pub MANUAL_SLICE_SIZE_CALCULATION,
complexity,
"manual slice size calculation"
}
declare_lint_pass!(ManualSliceSizeCalculation => [MANUAL_SLICE_SIZE_CALCULATION]);
impl<'tcx> LateLintPass<'tcx> for ManualSliceSizeCalculation {
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
// Does not apply inside const because size_of_val is not cost in stable.
if !in_constant(cx, expr.hir_id)
&& let ExprKind::Binary(ref op, left, right) = expr.kind
&& BinOpKind::Mul == op.node
&& !expr.span.from_expansion()
&& let Some(receiver) = simplify(cx, left, right)
{
let ctxt = expr.span.ctxt();
let mut app = Applicability::MachineApplicable;
let val_name = snippet_with_context(cx, receiver.span, ctxt, "slice", &mut app).0;
let Some(sugg) = std_or_core(cx) else { return };
span_lint_and_sugg(
cx,
MANUAL_SLICE_SIZE_CALCULATION,
expr.span,
"manual slice size calculation",
"try",
format!("{sugg}::mem::size_of_val({val_name})"),
app,
);
}
}
}
fn simplify<'tcx>(
cx: &LateContext<'tcx>,
expr1: &'tcx Expr<'tcx>,
expr2: &'tcx Expr<'tcx>,
) -> Option<&'tcx Expr<'tcx>> {
let expr1 = expr_or_init(cx, expr1);
let expr2 = expr_or_init(cx, expr2);
simplify_half(cx, expr1, expr2).or_else(|| simplify_half(cx, expr2, expr1))
}
fn simplify_half<'tcx>(
cx: &LateContext<'tcx>,
expr1: &'tcx Expr<'tcx>,
expr2: &'tcx Expr<'tcx>,
) -> Option<&'tcx Expr<'tcx>> {
if !expr1.span.from_expansion()
// expr1 is `[T1].len()`?
&& let ExprKind::MethodCall(method_path, receiver, _, _) = expr1.kind
&& method_path.ident.name == sym::len
&& let receiver_ty = cx.typeck_results().expr_ty(receiver)
&& let ty::Slice(ty1) = receiver_ty.peel_refs().kind()
// expr2 is `size_of::<T2>()`?
&& let ExprKind::Call(func, _) = expr2.kind
&& let ExprKind::Path(ref func_qpath) = func.kind
&& let Some(def_id) = cx.qpath_res(func_qpath, func.hir_id).opt_def_id()
&& cx.tcx.is_diagnostic_item(sym::mem_size_of, def_id)
&& let Some(ty2) = cx.typeck_results().node_args(func.hir_id).types().next()
// T1 == T2?
&& *ty1 == ty2
{
Some(receiver)
} else {
None
}
}