Fix micro_rpc cross workspace dependency

Add a manual test to check regressions in the future.

Ref project-oak#4573

Cargo.toml

@@ -4,7 +4,7 @@ members = [
   "linux_boot_params",
   "micro_rpc",
   "micro_rpc_build",
-  "micro_rpc_tests",
+  "micro_rpc_tests", "micro_rpc_workspace_test",
   "oak_attestation_verification",
   "oak_channel",
   "oak_client",

micro_rpc/build.rs

@@ -16,11 +16,8 @@
 
 fn main() {
     micro_rpc_build::compile(
-        &[format!(
-            "{}proto/micro_rpc/messages.proto",
-            env!("WORKSPACE_ROOT")
-        )],
-        &[env!("WORKSPACE_ROOT")],
+        &["../proto/micro_rpc/messages.proto"],
+        &["../proto"],
         Default::default(),
     );
 }

micro_rpc_workspace_test/.cargo/config.toml

@@ -0,0 +1,2 @@
+[env]
+WORKSPACE_ROOT = { value = "_invalid_workspace_root_" }

micro_rpc_workspace_test/Cargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "micro_rpc_workspace_test"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+micro_rpc = { path = "../micro_rpc" }

micro_rpc_workspace_test/README.md

@@ -0,0 +1,15 @@
+This directory contains a manual test to check whether the `micro_rpc` crate can
+be depended on from a crate in another workspace.
+
+See https://github.com/project-oak/oak/issues/4573 for context.
+
+This crate overwrites the `WORKSPACE_ROOT` env variable with an invalid value in
+the `.cargo/config.toml` file, which is necessary to shadow the corresponding
+one in the root of this repository, to simulate an external workspace that would
+not have that env variable set.
+
+To reproduce the issue, run the following command from the repository root:
+
+```bash
+env --chdir=./micro_rpc_workspace_test bash -c 'cargo clean && cargo build'
+```

micro_rpc_workspace_test/src/main.rs

@@ -0,0 +1,3 @@
+fn main() {
+    println!("Hello, world!");
+}