configurable cd hook

Signed-off-by: Ava Affine <ava@sunnypup.io>

src/stl/posix.rs

@@ -63,6 +63,7 @@ use {
 };
 
 pub const POSIX_LOAD_NAME: &str = "load";
+pub const CD_USER_CB: &str = "CFG_FLESH_CD_CB";
 
 pub struct ShellState {
     pub parent_pid: Pid,
@@ -714,38 +715,69 @@ fn fg_callback(
 }
 
 const CD_DOCSTRING: &str =
-    "Expects 1 argument (a string). Changes to a new directory";
+    "Expects 1 argument (a string). Changes to a new directory.
+If CFG_RELISH_CD_CB is defined, cd will evaluate it.
+cd returns the result that CFG_RELISH_CD_CB returns.";
 fn cd_callback(ast: &Seg, syms: &mut SymTable) -> Result<Ctr, Traceback> {
-    if let Ctr::String(ref dir) = *ast.car {
-        let dirp = Path::new(dir);
-        if let Err(s) = set_current_dir(dirp) {
-            Err(start_trace(
-                ("cd", s.to_string())
-                    .into()))
-        } else {
-            if let Ok(abs) = canonicalize(dirp) {
+    let dir: &String;
+    match *ast.car {
+        Ctr::String(ref d) => dir = d,
+        Ctr::Symbol(ref d) => dir = d,
+        Ctr::Seg(ref s) => {
+            match eval(s, syms) {
+                Ok(r) => {
+                    if r == ast.car {
+                        return Err(start_trace(("cd", "innapropriate input.").into()));
+                    }
+                    return cd_callback(&Seg::from_mono(r), syms);
+                }
+                Err(e) => {
+                    return Err(e.with_trace(("cd", "couldnt evaluate input").into()));
+                }
+            }
+        },
+        _ => return Err(start_trace(
+            ("cd", "expected input to be a string or symbol")
+                .into()))
+    }
+
+    let dirp = Path::new(dir);
+    match canonicalize(dirp) {
+        Ok(abs) => {
+            if let Err(s) = set_current_dir(dirp) {
+                Err(start_trace(
+                    ("cd", s.to_string())
+                        .into()))
+            } else {
                 syms.insert(
                     String::from("PWD"),
                     Symbol::from_ast(
                         &String::from("PWD"),
-                        &String::from("current working directory"),
+                        &String::from("current working directory, set by cd"),
                         &Seg::from_mono(Box::new(
                             Ctr::String(abs.to_string_lossy().into()))),
                         None,
                     ));
 
-                // Run configurable user function
-
-                Ok(Ctr::None)
-            } else {
-                Err(start_trace(
-                    ("cd", "cannot make absolute path").into()))
+                match syms.call_symbol(
+                    &CD_USER_CB.to_string(),
+                    &Seg::new(),
+                    true,
+                ) {
+                    Ok(r) => {
+                        Ok(*r)
+                    },
+                    Err(s) => {
+                        Err(s.with_trace(("cd", "failed to call callback").into()))
+                    },
+                }
             }
+        },
+        Err(e) => {
+            Err(
+                start_trace(    ("cd", e.to_string()).into())
+                    .with_trace(("cd", "could not make absolute path").into()))
         }
-    } else {
-        Err(start_trace(
-            ("cd", "expected input to be a string")
-                .into()))
     }
 }
 
@@ -948,11 +980,25 @@ pub fn load_posix_shell(syms: &mut SymTable, shell_state: Rc<RefCell<ShellState>
         "cd".to_string(),
         Symbol {
             name: String::from("cd"),
-            args: Args::Strict(vec![Type::String]),
-            conditional_branches: false,
+            args: Args::Lazy(1),
+            conditional_branches: true,
             docs: CD_DOCSTRING.to_string(),
             value: ValueType::Internal(Rc::new(cd_callback)),
             ..Default::default()
         },
     );
+
+    syms.insert(
+        String::from(CD_USER_CB),
+        Symbol {
+            name: String::from(CD_USER_CB),
+            args: Args::None,
+            conditional_branches: false,
+            docs: String::from("lambda called at each invocation of cd"),
+            value: ValueType::Internal(Rc::new(move |_ast: &Seg, _sym: &mut SymTable| -> Result<Ctr, Traceback> {
+                Ok(Ctr::None)
+            })),
+            ..Default::default()
+        },
+    );
 }