From 75894b27b14a2435800db8eed84d187aec272403 Mon Sep 17 00:00:00 2001
From: Sameer Kolhar <kolhar730@gmail.com>
Date: Sat, 26 Jun 2021 20:20:00 +0530
Subject: [PATCH 1/4] add feature flag for `type_changing_struct_update`

---
 compiler/rustc_feature/src/active.rs | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/compiler/rustc_feature/src/active.rs b/compiler/rustc_feature/src/active.rs
index 56a320c8d3bce..27c4b1968ad5e 100644
--- a/compiler/rustc_feature/src/active.rs
+++ b/compiler/rustc_feature/src/active.rs
@@ -666,6 +666,10 @@ declare_features! (
     /// Allows qualified paths in struct expressions, struct patterns and tuple struct patterns.
     (active, more_qualified_paths, "1.54.0", Some(80080), None),
 
+    /// Allows creation of instances of a struct by moving fields that have 
+    /// not changed from prior instances of the same struct (RFC #2528)
+    (active, type_changing_struct_update, "1.55.0", Some(86618), None)
+
     // -------------------------------------------------------------------------
     // feature-group-end: actual feature gates
     // -------------------------------------------------------------------------

From 609b5e5dbbf3ea8906a650ca59b7213d0c0ab59d Mon Sep 17 00:00:00 2001
From: Sameer Kolhar <kolhar730@gmail.com>
Date: Sat, 26 Jun 2021 20:32:05 +0530
Subject: [PATCH 2/4] remove trailing space in the file

---
 compiler/rustc_feature/src/active.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/compiler/rustc_feature/src/active.rs b/compiler/rustc_feature/src/active.rs
index 27c4b1968ad5e..d8e35ceb977b5 100644
--- a/compiler/rustc_feature/src/active.rs
+++ b/compiler/rustc_feature/src/active.rs
@@ -666,7 +666,7 @@ declare_features! (
     /// Allows qualified paths in struct expressions, struct patterns and tuple struct patterns.
     (active, more_qualified_paths, "1.54.0", Some(80080), None),
 
-    /// Allows creation of instances of a struct by moving fields that have 
+    /// Allows creation of instances of a struct by moving fields that have
     /// not changed from prior instances of the same struct (RFC #2528)
     (active, type_changing_struct_update, "1.55.0", Some(86618), None)
 

From 7dcadf74af0bb4ae9b02fe15d411307f158c5a0f Mon Sep 17 00:00:00 2001
From: Sameer Kolhar <kolhar730@gmail.com>
Date: Sun, 27 Jun 2021 11:09:05 +0530
Subject: [PATCH 3/4] add basic gate test for type_changing_struct_update

---
 .../basic_tests_setup.rs                      | 39 +++++++++++++++++++
 1 file changed, 39 insertions(+)
 create mode 100644 src/test/ui/type_changing_struct_update_rfc_2528/basic_tests_setup.rs

diff --git a/src/test/ui/type_changing_struct_update_rfc_2528/basic_tests_setup.rs b/src/test/ui/type_changing_struct_update_rfc_2528/basic_tests_setup.rs
new file mode 100644
index 0000000000000..02791ce491a46
--- /dev/null
+++ b/src/test/ui/type_changing_struct_update_rfc_2528/basic_tests_setup.rs
@@ -0,0 +1,39 @@
+// gate-test-type_changing_struct_update
+
+/// Here, we're documenting the current state of affairs related to
+/// FRU (functional record update)
+
+#![feature(type_changing_struct_update)]
+
+struct Machine<S> {
+    state: S,
+    common_field1: &'static str,
+    common_field2: i32,
+}
+
+struct State1;
+struct State2;
+
+impl Machine<State1> {
+    fn into_state2(self) -> Machine<State2> {
+        // do stuff
+        Machine {
+            state: State2,
+            ..self
+        }
+    }
+}
+
+#[test]
+#[should_panic]  // NOTE: this would be fixed by the implementation of the RFC
+fn update_to_state2() {
+    let m1: Machine<State1> = Machine {
+        state: State1,
+        common_field1: "hello",
+        common_field2: 2,
+    };
+    let m2: Machine<State2> = m1.into_state2();
+    assert_eq!(State2, m2.state);
+}
+
+fn main() {}

From b4226e4c6c99419b022f2d90659210350e62a0e9 Mon Sep 17 00:00:00 2001
From: Sameer Kolhar <kolhar730@gmail.com>
Date: Sun, 27 Jun 2021 11:09:23 +0530
Subject: [PATCH 4/4] add stderr file for basic_tests_setup

---
 .../basic_tests_setup.stderr                              | 8 ++++++++
 1 file changed, 8 insertions(+)
 create mode 100644 src/test/ui/type_changing_struct_update_rfc_2528/basic_tests_setup.stderr

diff --git a/src/test/ui/type_changing_struct_update_rfc_2528/basic_tests_setup.stderr b/src/test/ui/type_changing_struct_update_rfc_2528/basic_tests_setup.stderr
new file mode 100644
index 0000000000000..b9bb1d5d44a44
--- /dev/null
+++ b/src/test/ui/type_changing_struct_update_rfc_2528/basic_tests_setup.stderr
@@ -0,0 +1,8 @@
+error[E0308]: mismatched types
+  --> $DIR/basic_tests_setup.rs:19:15
+   |
+LL |             ..self
+   |               ^^^^ expected struct `State2`, found struct `State1`
+   |
+   = note: expected struct `Machine<State2>`
+              found struct `Machine<State1>`