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use super::READONLY_WRITE_LOCK;
use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::mir::{enclosing_mir, visit_local_usage};
use clippy_utils::source::snippet;
use clippy_utils::ty::is_type_diagnostic_item;
use rustc_errors::Applicability;
use rustc_hir::{Expr, ExprKind, Node, PatKind};
use rustc_lint::LateContext;
use rustc_middle::mir::{Location, START_BLOCK};
use rustc_span::sym;
fn is_unwrap_call(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
if let ExprKind::MethodCall(path, receiver, [], _) = expr.kind
&& path.ident.name == sym::unwrap
{
is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(receiver).peel_refs(), sym::Result)
} else {
false
}
}
pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, receiver: &Expr<'_>) {
if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(receiver).peel_refs(), sym::RwLock)
&& let Node::Expr(unwrap_call_expr) = cx.tcx.parent_hir_node(expr.hir_id)
&& is_unwrap_call(cx, unwrap_call_expr)
&& let parent = cx.tcx.parent_hir_node(unwrap_call_expr.hir_id)
&& let Node::LetStmt(local) = parent
&& let PatKind::Binding(.., ident, _) = local.pat.kind
// if the binding is prefixed with `_`, it typically means
// that this guard only exists to protect a section of code
// rather than the contained data
&& !ident.as_str().starts_with('_')
&& let Some(mir) = enclosing_mir(cx.tcx, expr.hir_id)
&& let Some((local, _)) = mir
.local_decls
.iter_enumerated()
.find(|(_, decl)| local.span.contains(decl.source_info.span))
&& let Some(usages) = visit_local_usage(
&[local],
mir,
Location {
block: START_BLOCK,
statement_index: 0,
},
)
&& let [usage] = usages.as_slice()
{
let writer_never_mutated = usage.local_consume_or_mutate_locs.is_empty();
if writer_never_mutated {
span_lint_and_sugg(
cx,
READONLY_WRITE_LOCK,
expr.span,
"this write lock is used only for reading",
"consider using a read lock instead",
format!("{}.read()", snippet(cx, receiver.span, "<receiver>")),
Applicability::MaybeIncorrect, // write lock might be intentional for enforcing exclusiveness
);
}
}
}
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