Make wasm-builder check before copy/write files if the content is the same (#6149)

* Make `wasm-builder` check before copy/write files if the content is the
same

* Update utils/wasm-builder/src/lib.rs

Co-authored-by: André Silva <123550+andresilva@users.noreply.github.com>

Co-authored-by: André Silva <123550+andresilva@users.noreply.github.com>

substrate/utils/wasm-builder/src/lib.rs

@@ -185,6 +185,17 @@ fn write_file_if_changed(file: PathBuf, content: String) {
 	}
 }
 
+/// Copy `src` to `dst` if the `dst` does not exist or is different.
+fn copy_file_if_changed(src: PathBuf, dst: PathBuf) {
+	let src_file = fs::read_to_string(&src).ok();
+	let dst_file = fs::read_to_string(&dst).ok();
+
+	if src_file != dst_file {
+		fs::copy(&src, &dst)
+			.expect(&format!("Copying `{}` to `{}` can not fail; qed", src.display(), dst.display()));
+	}
+}
+
 /// Get a cargo command that compiles with nightly
 fn get_nightly_cargo() -> CargoCommand {
 	let env_cargo = CargoCommand::new(

substrate/utils/wasm-builder/src/wasm_project.rs

@@ -302,10 +302,10 @@ fn create_wasm_workspace_project(wasm_workspace: &Path, workspace_root_path: &Pa
 		wasm_workspace_toml.insert("patch".into(), patch.into());
 	}
 
-	fs::write(
+	write_file_if_changed(
 		wasm_workspace.join("Cargo.toml"),
 		toml::to_string_pretty(&wasm_workspace_toml).expect("Wasm workspace toml is valid; qed"),
-	).expect("WASM workspace `Cargo.toml` writing can not fail; qed");
+	);
 }
 
 /// Get a list of enabled features for the project.
@@ -382,8 +382,7 @@ fn create_project(cargo_manifest: &Path, wasm_workspace: &Path, crate_metadata:
 
 	if let Some(crate_lock_file) = find_cargo_lock(cargo_manifest) {
 		// Use the `Cargo.lock` of the main project.
-		fs::copy(crate_lock_file, wasm_workspace.join("Cargo.lock"))
+		crate::copy_file_if_changed(crate_lock_file, wasm_workspace.join("Cargo.lock"));
-			.expect("Copying the `Cargo.lock` can not fail; qed");
 	}
 
 	project_folder