Expose `peel_casts` method as an util method inside `rustc_lint`

1 files changed, 55 insertions, 0 deletions

diff --git a/compiler/rustc_lint/src/utils.rs b/compiler/rustc_lint/src/utils.rs
new file mode 100644
index 00000000000..64bfa428ae4
--- /dev/null
+++ b/compiler/rustc_lint/src/utils.rs
@@ -0,0 +1,55 @@
+use rustc_hir::{Expr, ExprKind};
+use rustc_span::sym;
+
+use crate::LateContext;
+
+/// Given an expression, peel all of casts (`<expr> as ...`, `<expr>.cast{,_mut,_const}()`,
+/// `ptr::from_ref(<expr>)`, ...) and init expressions.
+///
+/// Returns the outermost expression and a boolean representing if one of the casts was
+/// `UnsafeCell::raw_get(<expr>)`
+pub(crate) fn peel_casts<'tcx>(
+    cx: &LateContext<'tcx>,
+    mut e: &'tcx Expr<'tcx>,
+) -> (&'tcx Expr<'tcx>, bool) {
+    let mut gone_trough_unsafe_cell_raw_get = false;
+
+    loop {
+        e = e.peel_blocks();
+        // <expr> as ...
+        e = if let ExprKind::Cast(expr, _) = e.kind {
+            expr
+        // <expr>.cast(), <expr>.cast_mut() or <expr>.cast_const()
+        } else if let ExprKind::MethodCall(_, expr, [], _) = e.kind
+            && let Some(def_id) = cx.typeck_results().type_dependent_def_id(e.hir_id)
+            && matches!(
+                cx.tcx.get_diagnostic_name(def_id),
+                Some(sym::ptr_cast | sym::const_ptr_cast | sym::ptr_cast_mut | sym::ptr_cast_const)
+            )
+        {
+            expr
+        // ptr::from_ref(<expr>), UnsafeCell::raw_get(<expr>) or mem::transmute<_, _>(<expr>)
+        } else if let ExprKind::Call(path, [arg]) = e.kind
+            && let ExprKind::Path(ref qpath) = path.kind
+            && let Some(def_id) = cx.qpath_res(qpath, path.hir_id).opt_def_id()
+            && matches!(
+                cx.tcx.get_diagnostic_name(def_id),
+                Some(sym::ptr_from_ref | sym::unsafe_cell_raw_get | sym::transmute)
+            )
+        {
+            if cx.tcx.is_diagnostic_item(sym::unsafe_cell_raw_get, def_id) {
+                gone_trough_unsafe_cell_raw_get = true;
+            }
+            arg
+        } else {
+            let init = cx.expr_or_init(e);
+            if init.hir_id != e.hir_id {
+                init
+            } else {
+                break;
+            }
+        };
+    }
+
+    (e, gone_trough_unsafe_cell_raw_get)
+}