Remove local non-workspace dependencies in workspace_members

Author: bjorn3

src/bootstrap/src/core/metadata.rs

@@ -5,7 +5,7 @@
 //! source, dependencies, targets, and available features. The collected metadata is then
 //! used to update the `Build` structure, ensuring proper dependency resolution and
 //! compilation flow.
-use std::collections::BTreeMap;
+use std::collections::{BTreeMap, HashSet};
 use std::path::PathBuf;
 
 use serde_derive::Deserialize;
@@ -89,7 +89,21 @@ fn workspace_members(build: &Build) -> Vec<Package> {
             .arg("--manifest-path")
             .arg(build.src.join(manifest_path));
         let metadata_output = cargo.run_always().run_capture_stdout(build).stdout();
-        let Output { packages, .. } = t!(serde_json::from_str(&metadata_output));
+        let Output { mut packages, .. } = t!(serde_json::from_str(&metadata_output));
+
+        // We need to remove local dependencies that exist outside of the workspace.
+        // This can happen when a package from the library workspace is directly
+        // depended on by the compiler, like for example proc_macro.
+        let local_deps =
+            packages.iter().map(|package| package.name.clone()).collect::<HashSet<_>>();
+        for package in &mut packages {
+            let () = package
+                .dependencies
+                .extract_if(.., |dep| !local_deps.contains(&dep.name))
+                .map(|_| ())
+                .collect();
+        }
+
         packages
     };