Auto merge of rust-lang#12508 - y21:issue12506, r=llogiq

Fix infinite loop in `cast_sign_loss` when peeling unwrap method calls

Fixes rust-lang#12506

The lint wants to peel method calls but didn't actually reassign the expression, leading to an infinite loop.

----

changelog: Fix infinite loop in [`cast_sign_loss`] when having two chained `.unwrap()` calls

Author: bors

src/tools/clippy/clippy_lints/src/casts/cast_sign_loss.rs

@@ -118,7 +118,7 @@ enum Sign {
     Uncertain,
 }
 
-fn expr_sign<'cx>(cx: &LateContext<'cx>, expr: &Expr<'_>, ty: impl Into<Option<Ty<'cx>>>) -> Sign {
+fn expr_sign<'cx, 'tcx>(cx: &LateContext<'cx>, mut expr: &'tcx Expr<'tcx>, ty: impl Into<Option<Ty<'cx>>>) -> Sign {
     // Try evaluate this expr first to see if it's positive
     if let Some(val) = get_const_signed_int_eval(cx, expr, ty) {
         return if val >= 0 { Sign::ZeroOrPositive } else { Sign::Negative };
@@ -134,11 +134,12 @@ fn expr_sign<'cx>(cx: &LateContext<'cx>, expr: &Expr<'_>, ty: impl Into<Option<T
         // Peel unwrap(), expect(), etc.
         while let Some(&found_name) = METHODS_UNWRAP.iter().find(|&name| &method_name == name)
             && let Some(arglist) = method_chain_args(expr, &[found_name])
-            && let ExprKind::MethodCall(inner_path, ..) = &arglist[0].0.kind
+            && let ExprKind::MethodCall(inner_path, recv, ..) = &arglist[0].0.kind
         {
             // The original type has changed, but we can't use `ty` here anyway, because it has been
             // moved.
             method_name = inner_path.ident.name.as_str();
+            expr = recv;
         }
 
         if METHODS_POW.iter().any(|&name| method_name == name)

src/tools/clippy/tests/ui/cast.rs

@@ -9,7 +9,12 @@
     clippy::cast_sign_loss,
     clippy::cast_possible_wrap
 )]
-#![allow(clippy::cast_abs_to_unsigned, clippy::no_effect, clippy::unnecessary_operation)]
+#![allow(
+    clippy::cast_abs_to_unsigned,
+    clippy::no_effect,
+    clippy::unnecessary_operation,
+    clippy::unnecessary_literal_unwrap
+)]
 
 fn main() {
     // Test clippy::cast_precision_loss
@@ -457,3 +462,8 @@ fn issue11642() {
         //~^ ERROR: casting `i32` to `u32` may lose the sign of the value
     }
 }
+
+fn issue12506() -> usize {
+    let bar: Result<Option<i64>, u32> = Ok(Some(10));
+    bar.unwrap().unwrap() as usize
+}