From df75a206bfbd13d38a131b9dac8cdea723af9897 Mon Sep 17 00:00:00 2001
From: AlekseyTs <AlekseyTs@users.noreply.github.com>
Date: Sat, 4 Dec 2021 07:34:46 -0800
Subject: [PATCH] Standardize list pattern lowering on `Index` constructor.
 (#5484)

Related to dotnet/roslyn#57825.
---
 proposals/list-patterns.md | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/proposals/list-patterns.md b/proposals/list-patterns.md
index 9e529915ae..a34a11abe8 100644
--- a/proposals/list-patterns.md
+++ b/proposals/list-patterns.md
@@ -78,19 +78,19 @@ The behavior of a pattern-matching operation is undefined if any of the above as
 
 #### Lowering
 
-A pattern of the form `expr is [1, 2, 3]` is equivalent to the following code (if compatible via implicit `Index` support):
+A pattern of the form `expr is [1, 2, 3]` is equivalent to the following code:
 ```cs
 expr.Length is 3
-&& expr[0] is 1
-&& expr[1] is 2
-&& expr[2] is 3
+&& expr[new Index(0, fromEnd: false)] is 1
+&& expr[new Index(1, fromEnd: false)] is 2
+&& expr[new Index(2, fromEnd: false)] is 3
 ```
 A *slice_pattern* acts like a proper discard i.e. no tests will be emitted for such pattern, rather it only affects other nodes, namely the length and indexer. For instance, a pattern of the form `expr is [1, .. var s, 3]`  is equivalent to the following code (if compatible via explicit `Index` and `Range` support):
 ```cs
 expr.Length is >= 2
-&& expr[new Index(0)] is 1
-&& expr[new Range(1, new Index(1, true))] is var s
-&& expr[new Index(1, true)] is 3
+&& expr[new Index(0, fromEnd: false)] is 1
+&& expr[new Range(new Index(1, fromEnd: false), new Index(1, fromEnd: true))] is var s
+&& expr[new Index(1, fromEnd: true)] is 3
 ```
 The *input type* for the *slice_pattern* is the return type of the underlying `this[Range]` or `Slice` method with two exceptions: For `string` and arrays, `string.Substring` and `RuntimeHelpers.GetSubArray` will be used, respectively.