canonicalize.patch

diff --git a/library/std/src/sys/pal/wasi/fs.rs b/library/std/src/sys/pal/wasi/fs.rs
index e8238665452..5f77b656894 100644
--- a/library/std/src/sys/pal/wasi/fs.rs
+++ b/library/std/src/sys/pal/wasi/fs.rs
@@ -1,6 +1,7 @@
 #![deny(unsafe_op_in_unsafe_fn)]
 
 use super::fd::WasiFd;
+use crate::env;
 use crate::ffi::{CStr, OsStr, OsString};
 use crate::fmt;
 use crate::io::{self, BorrowedCursor, IoSlice, IoSliceMut, SeekFrom};
@@ -652,10 +653,30 @@ fn metadata_at(fd: &WasiFd, flags: wasi::Lookupflags, path: &Path) -> io::Result
     Ok(FileAttr { meta })
 }
 
-pub fn canonicalize(_p: &Path) -> io::Result<PathBuf> {
-    // This seems to not be in wasi's API yet, and we may need to end up
-    // emulating it ourselves. For now just return an error.
-    unsupported()
+pub fn canonicalize(p: &Path) -> io::Result<PathBuf> {
+    fn __canonicalize(path: &Path, buf: &mut PathBuf) {
+        if path.is_absolute() {
+            buf.clear();
+        }
+        for part in path {
+            if part == ".." {
+                buf.pop();
+            } else if part != "." {
+                buf.push(part);
+                if let Ok(linkpath) = buf.read_link() {
+                    buf.pop();
+                    __canonicalize(&linkpath, buf);
+                }
+            }
+        }
+    }
+    let mut path = if p.is_absolute() {
+        PathBuf::new()
+    } else {
+        PathBuf::from(env::current_dir()?)
+    };
+    __canonicalize(p, &mut path);
+    Ok(path)
 }
 
 fn open_at(fd: &WasiFd, path: &Path, opts: &OpenOptions) -> io::Result<File> {