From d7077073648041ec505629b2f1df9ab800c422e2 Mon Sep 17 00:00:00 2001
From: Dylan MacKenzie <ecstaticmorse@gmail.com>
Date: Tue, 30 Nov 2021 14:56:26 -0800
Subject: [PATCH] Add "is" methods for projections to a given index

---
 compiler/rustc_middle/src/mir/mod.rs | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/compiler/rustc_middle/src/mir/mod.rs b/compiler/rustc_middle/src/mir/mod.rs
index a05b8a1da8d7..9fc12ad4a0b9 100644
--- a/compiler/rustc_middle/src/mir/mod.rs
+++ b/compiler/rustc_middle/src/mir/mod.rs
@@ -1803,6 +1803,16 @@ impl<V, T> ProjectionElem<V, T> {
             | Self::Downcast(_, _) => false,
         }
     }
+
+    /// Returns `true` if this is a `Downcast` projection with the given `VariantIdx`.
+    pub fn is_downcast_to(&self, v: VariantIdx) -> bool {
+        matches!(*self, Self::Downcast(_, x) if x == v)
+    }
+
+    /// Returns `true` if this is a `Field` projection with the given index.
+    pub fn is_field_to(&self, f: Field) -> bool {
+        matches!(*self, Self::Field(x, _) if x == f)
+    }
 }
 
 /// Alias for projections as they appear in places, where the base is a place