modify a mylib without rebuilding mybin

dynamic lib

configuration.nix

@@ -692,5 +692,17 @@ ccache
 #            });
 #        })];
 
+    #initially from: https://github.com/NixOS/nixpkgs/issues/300055#issuecomment-2034546410
+    #this works, well 'mybin' will use this variant of rebuilt mylib, without 'mybin' getting rebuilt.
+    system.replaceRuntimeDependencies = [({
+        original = pkgs.mylib;
+        replacement = pkgs.mylib.overrideAttrs (finalAttrs: prevAttrs: {
+        #(rec {
+            version = "0.1.3";
+            patches = prevAttrs.patches or [] ++ [
+              ./myoverlay/patches/testing1.patch
+            ];
+            });
+        })];
 }
 # vim: set tabstop=2 shiftwidth=2 expandtab :

myoverlay/default.nix

@@ -264,7 +264,7 @@ self: super:
 #      ];
 #  });
   mybin = super.rustPlatform.buildRustPackage rec {
-    name = "mybin";
+    pname = "mybin";
     version = "0.1.0";
     src = ./rustdylibusage/mybin/mybin-${version}.tar.gz;
     #cargoSha256 = "0qbdcw601m09fw7vqmafvw5q7w17dh37fbbycs6is3rff5qlmbyw"; #mybin
@@ -293,7 +293,7 @@ self: super:
 
   mylib = super.rustPlatform.buildRustPackage rec {
     version = "0.1.0";
-    name = "mylib";
+    pname = "mylib";
     src = ./rustdylibusage/mylib/mylib-${version}.tar.gz;
     #cargoSha256 = "1zwcx7637zl6ka058hfgwzmnxln1y592gfwiycxiz65qygxph383"; #mylib
     #cargoSha256 = "sha256-7AfdCKEh4xTyRir/hmA8I6WYnoPYAQH8NN1Jx19SYDc";

myoverlay/patches/testing1.patch

@@ -0,0 +1,13 @@
+diff --git a/myoverlay/rustdylibusage/mylib/src/lib.rs b/myoverlay/rustdylibusage/mylib/src/lib.rs
+index e1077a6..ea57df0 100644
+--- mylib/src/lib.rs
++++ mylib/src/lib.rs
+@@ -6,7 +6,7 @@ pub fn add(left: usize, right: usize) -> usize {
+ pub fn greet(name: &str) {
+ //#[no_mangle]
+ //pub extern "C" fn greet(name: *const std::os::raw::c_char) {
+-    println!("Hello, {}!", name);
++    println!("hAllo, {}!", name);
+ }
+
+