Adds explicit finalization and redirection link.

Author: Lichtso

proposals/0167-loader-v4.md

@@ -54,7 +54,7 @@ Accounts of programs owned by loader-v4 must have the following layout:
   - `u64` Slot in which the program was last deployed, retracted or
   initialized.
   - `[u8; 32]` Authority address which can send program management
-  instructions.
+  instructions. Or if the status is finalized, then the redirection link.
   - `u64` status enum:
     - Enum variant `0u64`: Retracted, program is in maintenance
     - Enum variant `1u64`: Deployed, program is ready to be executed
@@ -223,23 +223,41 @@ necessarily the current one, but the one of the epoch of the next slot
 - Instruction accounts:
   - `[writable]` The program account to change the authority of.
   - `[signer]` The current authority of the program.
-  - `[signer]` Optional, the new authority of the program.
+  - `[signer]` The new authority of the program.
 - Instruction data:
   - Enum variant `4u32`
+- Behavior:
+  - Check there are at least three instruction accounts,
+    otherwise throw `MissingAccount`
+  - Verify the program account
+  - Check that the new authority (instruction account at index 2)
+  signed as well, otherwise throw `MissingRequiredSignature`
+  - Check that the authority stored in the program account is different
+  from the one provided, otherwise throw `InvalidArgument`
+  - Copy the new authority address into the program account
+
+#### Finalize
+
+- Instruction accounts:
+  - `[writable]` The program account to change the authority of.
+  - `[signer]` The current authority of the program.
+  - `[]` Optional, the reserved address for the next version of the program.
+- Instruction data:
+  - Enum variant `5u32`
 - Behavior:
   - Check there are at least two instruction accounts,
     otherwise throw `MissingAccount`
   - Verify the program account
-  - In case a new authority was provided (instruction account at index 2):
-    - Check that it signed as well,
-    otherwise throw `MissingRequiredSignature`
-    - Check that the authority stored in the program account is different
-    from the one provided, otherwise throw `InvalidArgument`
-    - Copy the new authority address into the program account
-  - In case no new authority was provided:
-    - Check that the status stored in the program account is deployed,
+  - Check that the status stored in the program account is deployed,
     otherwise throw `InvalidArgument`
-    - Change the status stored in the program account to finalized
+  - In case the address of the next version was provided
+  (instruction account at index 2):
+    - Check that the previous and next version have different addresses,
+    otherwise throw `AccountBorrowFailed`
+    - Verify that program account as well
+    - Copy the address of the next version as redirection link stored in the
+    previous versions program account
+  - Change the status stored in the program account to finalized
 
 ## Impact