Fix protoc().parent() call

`Path::parent()` returns `None` for root and empty paths, so handle it
by panicking in this case.  In this case it should never happen under
non-contrived circumstances.

Signed-off-by: Tom Jakubowski <[email protected]>

Author: tomjakubowski

.github/actions/install-deps/action.yaml

@@ -54,8 +54,8 @@ runs:
               remove-haskell: "true"
               remove-codeql: "true"
 
+        # Sticking to 3.29 because of:
         # https://github.com/open-telemetry/opentelemetry-cpp/issues/2998
-        # Skip on arm64 Linux - use system cmake instead
         - name: Setup cmake
           # uses: jwlawson/actions-setup-cmake@v2
           uses: tomjakubowski/actions-setup-cmake@v0-aarch64-test4

rust/perspective-server/build.rs

@@ -46,7 +46,12 @@ fn cmake_build() -> Result<Option<PathBuf>, std::io::Error> {
     dst.define("ARROW_BUILD_EXAMPLES", "OFF");
     dst.define("RAPIDJSON_BUILD_EXAMPLES", "OFF");
     dst.define("ARROW_CXX_FLAGS_DEBUG", "-Wno-error");
-    dst.define("PSP_PROTOC_PATH", protoc().parent());
+    dst.define(
+        "PSP_PROTOC_PATH",
+        protoc()
+            .parent()
+            .expect("protoc() returned root path or empty string"),
+    );
     dst.define("CMAKE_COLOR_DIAGNOSTICS", "ON");
     dst.define(
         "PSP_PROTO_PATH",