Rollup merge of rust-lang#128815 - Nadrieril:is_stolen, r=jieyouxu,lcnr

Add `Steal::is_stolen()`

Writers of rustc drivers (such as myself) often encounter stealing issues. It is currently impossible to gracefully handle them. This PR adds a `Steal::is_stolen()` function for that purpose.

compiler/rustc_data_structures/src/steal.rs

@@ -51,6 +51,15 @@ impl<T> Steal<T> {
         let value = value_ref.take();
         value.expect("attempt to steal from stolen value")
     }
+
+    /// Writers of rustc drivers often encounter stealing issues. This function makes it possible to
+    /// handle these errors gracefully.
+    ///
+    /// This should not be used within rustc as it leaks information not tracked
+    /// by the query system, breaking incremental compilation.
+    pub fn is_stolen(&self) -> bool {
+        self.value.borrow().is_none()
+    }
 }
 
 impl<CTX, T: HashStable<CTX>> HashStable<CTX> for Steal<T> {