Replace hard linked metadata.rmeta with a copy when finalizing the incremental compilation session dir fails

compiler/rustc_incremental/src/persist/fs.rs

@@ -115,6 +115,8 @@ use rustc_data_structures::svh::Svh;
 use rustc_data_structures::unord::{UnordMap, UnordSet};
 use rustc_data_structures::{base_n, flock};
 use rustc_fs_util::{LinkOrCopy, link_or_copy, try_canonicalize};
+use rustc_middle::dep_graph::WorkProduct;
+use rustc_session::config::OutputType;
 use rustc_session::{IncrCompSession, Session, StableCrateId};
 use rustc_span::{Symbol, bug};
 use tracing::debug;
@@ -332,7 +334,31 @@ pub fn finalize_session_directory(
     let new_path = incr_comp_session_dir.parent().unwrap().join(&*sub_dir_name);
     debug!("finalize_session_directory() - new path: {}", new_path.display());
 
-    match rename_path_with_retry(&*incr_comp_session_dir, &new_path, 3) {
+    let result = std_fs::rename(&*incr_comp_session_dir, &new_path).or_else(|e| {
+        if !cfg!(windows) || e.kind() != ErrorKind::PermissionDenied {
+            return Err(e);
+        }
+
+        // On ReFS, renaming a directory that contains a hard link to the metadata workproduct file
+        // can fail if it is being used by another process (such as another rustc instance).
+        // As a fallback, we try to replace the hard link with a copy, which should allow the
+        // rename to succeed.
+        // See https://github.com/rust-lang/rust/issues/151181
+        if let Err(err) = replace_hard_link_with_copy(&in_incr_comp_dir_sess(
+            &incr_comp_session,
+            &format!(
+                "{}.{}",
+                WorkProduct::METADATA_WORKPRODUCT_CGU_NAME,
+                OutputType::Metadata.extension()
+            ),
+        )) {
+            debug!("finalize_session_directory() - error replacing hard link with copy: {}", err);
+        }
+
+        rename_path_with_retry(&*incr_comp_session_dir, &new_path, 3)
+    });
+
+    match result {
         Ok(_) => {
             debug!("finalize_session_directory() - directory renamed successfully");
         }
@@ -893,3 +919,15 @@ fn rename_path_with_retry(from: &Path, to: &Path, mut retries_left: usize) -> st
         }
     }
 }
+
+/// Turns a hard link of the file at `path` into a copy.
+fn replace_hard_link_with_copy(path: &Path) -> std::io::Result<()> {
+    let tmp_name = path.with_added_extension("tmp");
+
+    // In case a stale temporary file was linked from a previous failed attempt.
+    safe_remove_file(&tmp_name)?;
+
+    std_fs::copy(path, &tmp_name).and_then(|_| std_fs::rename(&tmp_name, path)).inspect_err(|_| {
+        let _ = safe_remove_file(&tmp_name);
+    })
+}

compiler/rustc_incremental/src/persist/fs/tests.rs

@@ -75,3 +75,18 @@ fn test_find_source_directory_in_iter() {
         None
     );
 }
+
+#[test]
+fn test_replace_hard_link_with_copy_unshares_hard_link() {
+    let dir = rustc_fs_util::TempDirBuilder::new().tempdir_in(std::env::temp_dir()).unwrap();
+    let file = dir.path().join("file");
+    let link = dir.path().join("link");
+    std_fs::write(&file, b"original").unwrap();
+    std_fs::hard_link(&file, &link).unwrap();
+
+    replace_hard_link_with_copy(&link).unwrap();
+
+    std_fs::write(&file, b"changed").unwrap();
+    assert_eq!(std_fs::read(&link).unwrap(), b"original");
+    assert!(!link.with_added_extension("tmp").exists());
+}

compiler/rustc_interface/src/queries.rs

@@ -7,7 +7,7 @@ use rustc_data_structures::svh::Svh;
 use rustc_errors::timings::TimingSection;
 use rustc_hir::def_id::LOCAL_CRATE;
 use rustc_metadata::EncodedMetadata;
-use rustc_middle::dep_graph::{DepGraph, WorkProductMap};
+use rustc_middle::dep_graph::{DepGraph, WorkProduct, WorkProductMap};
 use rustc_middle::ty::TyCtxt;
 use rustc_session::config::{self, OutputFilenames, OutputType};
 use rustc_session::{IncrCompSession, Session};
@@ -99,8 +99,8 @@ impl Linker {
             let (id, product) = rustc_incremental::copy_cgu_workproduct_to_incr_comp_cache_dir(
                 sess,
                 incr_comp_session.as_ref().unwrap(),
-                "metadata",
-                &[("rmeta", path)],
+                WorkProduct::METADATA_WORKPRODUCT_CGU_NAME,
+                &[(OutputType::Metadata.extension(), path)],
                 &[],
             );
             work_products.insert(id, product);

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -18,7 +18,7 @@ use rustc_hir::def_id::{CRATE_DEF_ID, LOCAL_CRATE, LocalDefId, LocalDefIdSet};
 use rustc_hir::definitions::DefPathData;
 use rustc_hir::find_attr;
 use rustc_hir_pretty::id_to_string;
-use rustc_middle::dep_graph::WorkProductId;
+use rustc_middle::dep_graph::{WorkProduct, WorkProductId};
 use rustc_middle::middle::dependency_format::Linkage;
 use rustc_middle::mir::interpret;
 use rustc_middle::query::Providers;
@@ -28,7 +28,7 @@ use rustc_middle::ty::codec::TyEncoder;
 use rustc_middle::ty::fast_reject::{self, TreatParams};
 use rustc_serialize::{Decodable, Decoder, Encodable, Encoder, opaque};
 use rustc_session::config::mitigation_coverage::DeniedPartialMitigation;
-use rustc_session::config::{OptLevel, TargetModifier};
+use rustc_session::config::{OptLevel, OutputType, TargetModifier};
 use rustc_span::def_id::CRATE_MOD_ID;
 use rustc_span::hygiene::HygieneEncodeContext;
 use rustc_span::{
@@ -2502,11 +2502,12 @@ pub fn encode_metadata(tcx: TyCtxt<'_>, path: &Path, ref_path: Option<&Path>) {
 
     // If the metadata dep-node is green, try to reuse the saved work product.
     if tcx.dep_graph.is_fully_enabled()
-        && let work_product_id = WorkProductId::from_cgu_name("metadata")
+        && let work_product_id =
+            WorkProductId::from_cgu_name(WorkProduct::METADATA_WORKPRODUCT_CGU_NAME)
         && let Some(work_product) = tcx.dep_graph.previous_work_product(&work_product_id)
         && tcx.dep_graph.try_mark_green(tcx, &dep_node).is_some()
     {
-        let saved_path = &work_product.saved_files["rmeta"];
+        let saved_path = &work_product.saved_files[OutputType::Metadata.extension()];
         let incr_comp_session_dir = &tcx.incr_comp_session.unwrap().session_directory;
         let source_file_in_incr_dir = &incr_comp_session_dir.join(saved_path);
         debug!("copying preexisting metadata from {source_file_in_incr_dir:?} to {path:?}");

compiler/rustc_middle/src/dep_graph/graph.rs

@@ -1143,6 +1143,13 @@ pub struct WorkProduct {
     pub saved_files: UnordMap<String, String>,
 }
 
+impl WorkProduct {
+    /// The metadata work product is not produced by any CGU and thus its
+    /// name cannot be derived from `CodegenUnit`. Both the writers and readers
+    /// of the metadata work product use this constant to agree on the name.
+    pub const METADATA_WORKPRODUCT_CGU_NAME: &str = "metadata";
+}
+
 pub type WorkProductMap = UnordMap<WorkProductId, WorkProduct>;
 
 // Index type for `DepNodeData`'s edges.