--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/rust/hg-core/src/checkexec.rs	Thu Jan 05 17:15:03 2023 +0000
@@ -0,0 +1,111 @@
+use std::fs;
+use std::io;
+use std::os::unix::fs::{MetadataExt, PermissionsExt};
+use std::path::Path;
+
+// This is a rust rewrite of [checkexec] function from [posix.py]
+
+const EXECFLAGS: u32 = 0o111;
+
+fn is_executable(path: impl AsRef<Path>) -> Result<bool, io::Error> {
+    let metadata = fs::metadata(path)?;
+    let mode = metadata.mode();
+    Ok(mode & EXECFLAGS != 0)
+}
+
+fn make_executable(path: impl AsRef<Path>) -> Result<(), io::Error> {
+    let mode = fs::metadata(path.as_ref())?.mode();
+    fs::set_permissions(
+        path,
+        fs::Permissions::from_mode((mode & 0o777) | EXECFLAGS),
+    )?;
+    Ok(())
+}
+
+fn copy_mode(
+    src: impl AsRef<Path>,
+    dst: impl AsRef<Path>,
+) -> Result<(), io::Error> {
+    let mode = match fs::symlink_metadata(src) {
+        Ok(metadata) => metadata.mode(),
+        Err(e) if e.kind() == io::ErrorKind::NotFound =>
+        // copymode in python has a more complicated handling of FileNotFound
+        // error, which we don't need because all it does is applying
+        // umask, which the OS already does when we mkdir.
+        {
+            return Ok(())
+        }
+        Err(e) => return Err(e),
+    };
+    fs::set_permissions(dst, fs::Permissions::from_mode(mode))?;
+    Ok(())
+}
+
+fn check_exec_impl(path: impl AsRef<Path>) -> Result<bool, io::Error> {
+    let basedir = path.as_ref().join(".hg");
+    let cachedir = basedir.join("wcache");
+    let storedir = basedir.join("store");
+
+    if !cachedir.exists() {
+        fs::create_dir(&cachedir)
+            .and_then(|()| {
+                if storedir.exists() {
+                    copy_mode(&storedir, &cachedir)
+                } else {
+                    copy_mode(&basedir, &cachedir)
+                }
+            })
+            .ok();
+    }
+
+    let leave_file: bool;
+    let checkdir: &Path;
+    let checkisexec = cachedir.join("checkisexec");
+    let checknoexec = cachedir.join("checknoexec");
+    if cachedir.is_dir() {
+        match is_executable(&checkisexec) {
+            Err(e) if e.kind() == io::ErrorKind::NotFound => (),
+            Err(e) => return Err(e),
+            Ok(is_exec) => {
+                if is_exec {
+                    let noexec_is_exec = match is_executable(&checknoexec) {
+                        Err(e) if e.kind() == io::ErrorKind::NotFound => {
+                            fs::write(&checknoexec, "")?;
+                            is_executable(&checknoexec)?
+                        }
+                        Err(e) => return Err(e),
+                        Ok(exec) => exec,
+                    };
+                    if !noexec_is_exec {
+                        // check-exec is exec and check-no-exec is not exec
+                        return Ok(true);
+                    }
+                    fs::remove_file(&checknoexec)?;
+                }
+                fs::remove_file(&checkisexec)?;
+            }
+        }
+        checkdir = &cachedir;
+        leave_file = true;
+    } else {
+        checkdir = path.as_ref();
+        leave_file = false;
+    };
+
+    let tmp_file = tempfile::NamedTempFile::new_in(checkdir)?;
+    if !is_executable(tmp_file.path())? {
+        make_executable(tmp_file.path())?;
+        if is_executable(tmp_file.path())? {
+            if leave_file {
+                tmp_file.persist(checkisexec).ok();
+            }
+            return Ok(true);
+        }
+    }
+
+    Ok(false)
+}
+
+pub fn check_exec(path: impl AsRef<Path>) -> bool {
+    check_exec_impl(path).unwrap_or(false)
+}