Prevent the invariant prefix optimization from defying the walk behavior

src/walk/glob.rs

@@ -190,7 +190,22 @@ impl<'t> Glob<'t> {
                 None
             }
             else {
-                Some(prefix.into())
+                // here, we don't know if the glob will be walked with or without symlinks,
+                // so we need to ensure that the invariant prefix optimisation doesn't cross a
+                // symlink todo: `anchor` knows nothing about the walk behaviour. if it did, we
+                // could probably skip this conditionally for a small perf bonus
+                let prefix: PathBuf = prefix.into();
+                let mut curr_prefix = prefix.as_path();
+                let mut last_symlink = curr_prefix;
+                while let Some(parent) = curr_prefix.parent() {
+                    if parent.is_symlink() {
+                        last_symlink = parent;
+                    }
+                    curr_prefix = parent;
+                }
+                // we found the last symlink, but we need the chance to
+                // filter it, so take the parent one more time
+                Some(last_symlink.parent().unwrap_or(last_symlink).into())
             }
         }