fix: fixcd (#6799)

* fix: fixcd

try to fix

Log: try to fix the bug with can enter a permisson error fold

* change wording

* fat

* fmt

Co-authored-by: Darren Schroeder <343840+fdncred@users.noreply.github.com>

crates/nu-command/src/filesystem/cd.rs

@@ -6,6 +6,29 @@ use nu_protocol::engine::{Command, EngineState, Stack};
 use nu_protocol::{
     Category, Example, PipelineData, ShellError, Signature, Spanned, SyntaxShape, Value,
 };
+use std::path::Path;
+
+// when the file under the fold executeable
+#[cfg(unix)]
+mod permission_mods {
+    pub type Mode = u32;
+    pub mod unix {
+        use super::Mode;
+        pub const USER_EXECUTE: Mode = libc::S_IXUSR as Mode;
+        pub const GROUP_EXECUTE: Mode = libc::S_IXGRP as Mode;
+        pub const OTHER_EXECUTE: Mode = libc::S_IXOTH as Mode;
+    }
+}
+
+// use to return the message of the result of change director
+// TODO: windows, maybe should use file_attributes function in https://doc.rust-lang.org/std/os/windows/fs/trait.MetadataExt.html
+// TODO: the meaning of the result of the function can be found in https://learn.microsoft.com/en-us/windows/win32/fileio/file-attribute-constants
+// TODO: if have realize the logic on windows, remove the cfg
+#[derive(Debug)]
+enum PermissionResult<'a> {
+    PermissionOk,
+    PermissionDenied(&'a str),
+}
 
 #[derive(Clone)]
 pub struct Cd;
@@ -141,6 +164,7 @@ impl Command for Cd {
             }
         };
 
+        let path_tointo = path.clone();
         let path_value = Value::String { val: path, span };
         let cwd = Value::String {
             val: cwd.to_string_lossy().to_string(),
@@ -172,9 +196,16 @@ impl Command for Cd {
 
         //FIXME: this only changes the current scope, but instead this environment variable
         //should probably be a block that loads the information from the state in the overlay
-
-        stack.add_env_var("PWD".into(), path_value);
-        Ok(PipelineData::new(call.head))
+        match have_permission(&path_tointo) {
+            PermissionResult::PermissionOk => {
+                stack.add_env_var("PWD".into(), path_value);
+                Ok(PipelineData::new(call.head))
+            }
+            PermissionResult::PermissionDenied(reason) => Err(ShellError::IOError(format!(
+                "Cannot change directory to {}: {}",
+                path_tointo, reason
+            ))),
+        }
     }
 
     fn examples(&self) -> Vec<Example> {
@@ -197,3 +228,65 @@ impl Command for Cd {
         ]
     }
 }
+#[cfg(windows)]
+fn have_permission(dir: impl AsRef<Path>) -> PermissionResult<'static> {
+    match dir.as_ref().read_dir() {
+        Err(e) => {
+            if matches!(e.kind(), std::io::ErrorKind::PermissionDenied) {
+                PermissionResult::PermissionDenied("Folder is unable to be read")
+            } else {
+                PermissionResult::PermissionOk
+            }
+        }
+        Ok(_) => PermissionResult::PermissionOk,
+    }
+}
+
+#[cfg(unix)]
+fn have_permission(dir: impl AsRef<Path>) -> PermissionResult<'static> {
+    match dir.as_ref().metadata() {
+        Ok(metadata) => {
+            use std::os::unix::fs::MetadataExt;
+            let bits = metadata.mode();
+            let has_bit = |bit| bits & bit == bit;
+            let current_user = users::get_current_uid();
+            if current_user == 0 {
+                return PermissionResult::PermissionOk;
+            }
+            let current_group = users::get_current_gid();
+            let owner_user = metadata.uid();
+            let owner_group = metadata.gid();
+            match (current_user == owner_user, current_group == owner_group) {
+                (true, _) => {
+                    if has_bit(permission_mods::unix::USER_EXECUTE) {
+                        PermissionResult::PermissionOk
+                    } else {
+                        PermissionResult::PermissionDenied(
+                            "You are the owner but do not have the execute permission",
+                        )
+                    }
+                }
+                (false, true) => {
+                    if has_bit(permission_mods::unix::GROUP_EXECUTE) {
+                        PermissionResult::PermissionOk
+                    } else {
+                        PermissionResult::PermissionDenied(
+                            "You are in the group but do not have the execute permission",
+                        )
+                    }
+                }
+                // other_user or root
+                (false, false) => {
+                    if has_bit(permission_mods::unix::OTHER_EXECUTE) {
+                        PermissionResult::PermissionOk
+                    } else {
+                        PermissionResult::PermissionDenied(
+                            "You are neither the owner, in the group, nor the super user and do not have permission",
+                        )
+                    }
+                }
+            }
+        }
+        Err(_) => PermissionResult::PermissionDenied("Could not retrieve the metadata"),
+    }
+}