Fix proc-macro-test-impl building without any proc-macros

Cargo.lock

@@ -1304,14 +1304,9 @@ name = "proc-macro-test"
 version = "0.0.0"
 dependencies = [
  "cargo_metadata",
- "proc-macro-test-impl",
  "toolchain",
 ]
 
-[[package]]
-name = "proc-macro-test-impl"
-version = "0.0.0"
-
 [[package]]
 name = "proc-macro2"
 version = "1.0.69"

crates/proc-macro-srv/proc-macro-test/Cargo.toml

@@ -12,10 +12,8 @@ doctest = false
 [build-dependencies]
 cargo_metadata = "0.18.1"
 
-proc-macro-test-impl = { path = "imp", version = "0.0.0" }
-
 # local deps
-toolchain.path = "../../toolchain"
+toolchain = { path = "../../toolchain", version = "0.0.0" }
 
 [features]
-sysroot-abi = ["proc-macro-test-impl/sysroot-abi"]
+sysroot-abi = []

crates/proc-macro-srv/proc-macro-test/build.rs

@@ -70,6 +70,9 @@ fn main() {
         // instance to use the same target directory.
         .arg("--target-dir")
         .arg(&target_dir);
+    if cfg!(feature = "sysroot-abi") {
+        cmd.args(["--features", "sysroot-abi"]);
+    }
 
     if let Ok(target) = std::env::var("TARGET") {
         cmd.args(["--target", &target]);

crates/proc-macro-srv/src/proc_macros.rs

@@ -97,7 +97,7 @@ impl ProcMacros {
             }
         }
 
-        Err(bridge::PanicMessage::String("Nothing to expand".to_string()).into())
+        Err(bridge::PanicMessage::String(format!("proc-macro `{macro_name}` is missing")).into())
     }
 
     pub(crate) fn list_macros(&self) -> Vec<(String, ProcMacroKind)> {