wasm-builder: Improve workspace handling (#10700)

When building a wasm binary from a different repo inside a local workspace, we did not used the
correct `Cargo.toml` to find the correct patches and features. The solution to this is to just walk
up from the target directory until we find the workspace we are currently compiling. If this
heuristic isn't working, we print a warning and let the user set an env variable
`WASM_BUILD_WORKSPACE_HINT` to tell the `wasm-builder` where the actual workspace is.

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

@@ -77,6 +77,15 @@ fn crate_metadata(cargo_manifest: &Path) -> Metadata {
 
 	let cargo_lock_existed = cargo_lock.exists();
 
+	// If we can find a `Cargo.lock`, we assume that this is the workspace root and there exists a
+	// `Cargo.toml` that we can use for getting the metadata.
+	let cargo_manifest = if let Some(mut cargo_lock) = find_cargo_lock(cargo_manifest) {
+		cargo_lock.set_file_name("Cargo.toml");
+		cargo_lock
+	} else {
+		cargo_manifest.to_path_buf()
+	};
+
 	let crate_metadata = MetadataCommand::new()
 		.manifest_path(cargo_manifest)
 		.exec()
@@ -151,18 +160,29 @@ fn find_cargo_lock(cargo_manifest: &Path) -> Option<PathBuf> {
 		}
 	}
 
+	if let Ok(workspace) = env::var(crate::WASM_BUILD_WORKSPACE_HINT) {
+		let path = PathBuf::from(workspace);
+
+		if path.join("Cargo.lock").exists() {
+			return Some(path.join("Cargo.lock"))
+		} else {
+			build_helper::warning!(
+				"`{}` env variable doesn't point to a directory that contains a `Cargo.lock`.",
+				crate::WASM_BUILD_WORKSPACE_HINT,
+			);
+		}
+	}
+
 	if let Some(path) = find_impl(build_helper::out_dir()) {
 		return Some(path)
 	}
 
-	if let Some(path) = find_impl(cargo_manifest.to_path_buf()) {
-		return Some(path)
-	}
-
 	build_helper::warning!(
-		"Could not find `Cargo.lock` for `{}`, while searching from `{}`.",
+		"Could not find `Cargo.lock` for `{}`, while searching from `{}`. \
+		 To fix this, point the `{}` env variable to the directory of the workspace being compiled.",
 		cargo_manifest.display(),
-		build_helper::out_dir().display()
+		build_helper::out_dir().display(),
+		crate::WASM_BUILD_WORKSPACE_HINT,
 	);
 
 	None