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use clippy_utils::consts::ConstEvalCtxt;
use clippy_utils::diagnostics::span_lint;
use clippy_utils::macros::{is_assert_macro, root_macro_call};
use clippy_utils::{find_binding_init, get_parent_expr, is_inside_always_const_context, path_to_local};
use rustc_hir::{Expr, HirId};
use rustc_lint::{LateContext, LintContext};
use rustc_span::sym;
use super::CONST_IS_EMPTY;
/// Expression whose initialization depend on a constant conditioned by a `#[cfg(…)]` directive will
/// not trigger the lint.
pub(super) fn check(cx: &LateContext<'_>, expr: &'_ Expr<'_>, receiver: &Expr<'_>) {
if expr.span.in_external_macro(cx.sess().source_map()) || !receiver.span.eq_ctxt(expr.span) {
return;
}
if let Some(parent) = get_parent_expr(cx, expr) {
if let Some(parent) = get_parent_expr(cx, parent) {
if is_inside_always_const_context(cx.tcx, expr.hir_id)
&& let Some(macro_call) = root_macro_call(parent.span)
&& is_assert_macro(cx, macro_call.def_id)
{
return;
}
}
}
let init_expr = expr_or_init(cx, receiver);
if !receiver.span.eq_ctxt(init_expr.span) {
return;
}
if let Some(init_is_empty) = ConstEvalCtxt::new(cx).eval_is_empty(init_expr) {
span_lint(
cx,
CONST_IS_EMPTY,
expr.span,
format!("this expression always evaluates to {init_is_empty:?}"),
);
}
}
fn is_under_cfg(cx: &LateContext<'_>, id: HirId) -> bool {
cx.tcx
.hir()
.parent_id_iter(id)
.any(|id| cx.tcx.hir().attrs(id).iter().any(|attr| attr.has_name(sym::cfg)))
}
/// Similar to [`clippy_utils::expr_or_init`], but does not go up the chain if the initialization
/// value depends on a `#[cfg(…)]` directive.
fn expr_or_init<'a, 'b, 'tcx: 'b>(cx: &LateContext<'tcx>, mut expr: &'a Expr<'b>) -> &'a Expr<'b> {
while let Some(init) = path_to_local(expr)
.and_then(|id| find_binding_init(cx, id))
.filter(|init| cx.typeck_results().expr_adjustments(init).is_empty())
.filter(|init| !is_under_cfg(cx, init.hir_id))
{
expr = init;
}
expr
}
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