1 files changed, 79 insertions, 0 deletions
diff --git a/cli/fs_util.rs b/cli/fs_util.rs
index fa1535469..843f5e0cf 100644
--- a/cli/fs_util.rs
+++ b/cli/fs_util.rs
@@ -15,6 +15,7 @@ use std::io::ErrorKind;
 use std::io::Write;
 use std::path::Path;
 use std::path::PathBuf;
+use std::time::Duration;
 use walkdir::WalkDir;
 
 pub fn atomic_write_file<T: AsRef<[u8]>>(
@@ -357,6 +358,84 @@ pub fn copy_dir_recursive(from: &Path, to: &Path) -> Result<(), AnyError> {
   Ok(())
 }
 
+/// Hardlinks the files in one directory to another directory.
+///
+/// Note: Does not handle symlinks.
+pub fn hard_link_dir_recursive(from: &Path, to: &Path) -> Result<(), AnyError> {
+  std::fs::create_dir_all(&to)
+    .with_context(|| format!("Creating {}", to.display()))?;
+  let read_dir = std::fs::read_dir(&from)
+    .with_context(|| format!("Reading {}", from.display()))?;
+
+  for entry in read_dir {
+    let entry = entry?;
+    let file_type = entry.file_type()?;
+    let new_from = from.join(entry.file_name());
+    let new_to = to.join(entry.file_name());
+
+    if file_type.is_dir() {
+      hard_link_dir_recursive(&new_from, &new_to).with_context(|| {
+        format!("Dir {} to {}", new_from.display(), new_to.display())
+      })?;
+    } else if file_type.is_file() {
+      // note: chance for race conditions here between attempting to create,
+      // then removing, then attempting to create. There doesn't seem to be
+      // a way to hard link with overwriting in Rust, but maybe there is some
+      // way with platform specific code. The workaround here is to handle
+      // scenarios where something else might create or remove files.
+      if let Err(err) = std::fs::hard_link(&new_from, &new_to) {
+        if err.kind() == ErrorKind::AlreadyExists {
+          if let Err(err) = std::fs::remove_file(&new_to) {
+            if err.kind() == ErrorKind::NotFound {
+              // Assume another process/thread created this hard link to the file we are wanting
+              // to remove then sleep a little bit to let the other process/thread move ahead
+              // faster to reduce contention.
+              std::thread::sleep(Duration::from_millis(10));
+            } else {
+              return Err(err).with_context(|| {
+                format!(
+                  "Removing file to hard link {} to {}",
+                  new_from.display(),
+                  new_to.display()
+                )
+              });
+            }
+          }
+
+          // Always attempt to recreate the hardlink. In contention scenarios, the other process
+          // might have been killed or exited after removing the file, but before creating the hardlink
+          if let Err(err) = std::fs::hard_link(&new_from, &new_to) {
+            // Assume another process/thread created this hard link to the file we are wanting
+            // to now create then sleep a little bit to let the other process/thread move ahead
+            // faster to reduce contention.
+            if err.kind() == ErrorKind::AlreadyExists {
+              std::thread::sleep(Duration::from_millis(10));
+            } else {
+              return Err(err).with_context(|| {
+                format!(
+                  "Hard linking {} to {}",
+                  new_from.display(),
+                  new_to.display()
+                )
+              });
+            }
+          }
+        } else {
+          return Err(err).with_context(|| {
+            format!(
+              "Hard linking {} to {}",
+              new_from.display(),
+              new_to.display()
+            )
+          });
+        }
+      }
+    }
+  }
+
+  Ok(())
+}
+
 pub fn symlink_dir(oldpath: &Path, newpath: &Path) -> Result<(), AnyError> {
   let err_mapper = |err: Error| {
     Error::new(