Allow parse-time evaluation of calls, pipelines and subexpressions (#9499)

Co-authored-by: Antoine Stevan <44101798+amtoine@users.noreply.github.com>

crates/nu-engine/src/call_ext.rs

@@ -1,6 +1,7 @@
 use nu_protocol::{
     ast::Call,
-    engine::{EngineState, Stack},
+    engine::{EngineState, Stack, StateWorkingSet},
+    eval_const::eval_constant,
     FromValue, ShellError,
 };
 
@@ -14,6 +15,12 @@ pub trait CallExt {
         name: &str,
     ) -> Result<Option<T>, ShellError>;
 
+    fn get_flag_const<T: FromValue>(
+        &self,
+        working_set: &StateWorkingSet,
+        name: &str,
+    ) -> Result<Option<T>, ShellError>;
+
     fn rest<T: FromValue>(
         &self,
         engine_state: &EngineState,
@@ -21,6 +28,12 @@ pub trait CallExt {
         starting_pos: usize,
     ) -> Result<Vec<T>, ShellError>;
 
+    fn rest_const<T: FromValue>(
+        &self,
+        working_set: &StateWorkingSet,
+        starting_pos: usize,
+    ) -> Result<Vec<T>, ShellError>;
+
     fn opt<T: FromValue>(
         &self,
         engine_state: &EngineState,
@@ -35,6 +48,12 @@ pub trait CallExt {
         pos: usize,
     ) -> Result<T, ShellError>;
 
+    fn req_const<T: FromValue>(
+        &self,
+        working_set: &StateWorkingSet,
+        pos: usize,
+    ) -> Result<T, ShellError>;
+
     fn req_parser_info<T: FromValue>(
         &self,
         engine_state: &EngineState,
@@ -58,6 +77,19 @@ impl CallExt for Call {
         }
     }
 
+    fn get_flag_const<T: FromValue>(
+        &self,
+        working_set: &StateWorkingSet,
+        name: &str,
+    ) -> Result<Option<T>, ShellError> {
+        if let Some(expr) = self.get_flag_expr(name) {
+            let result = eval_constant(working_set, &expr)?;
+            FromValue::from_value(&result).map(Some)
+        } else {
+            Ok(None)
+        }
+    }
+
     fn rest<T: FromValue>(
         &self,
         engine_state: &EngineState,
@@ -74,6 +106,21 @@ impl CallExt for Call {
         Ok(output)
     }
 
+    fn rest_const<T: FromValue>(
+        &self,
+        working_set: &StateWorkingSet,
+        starting_pos: usize,
+    ) -> Result<Vec<T>, ShellError> {
+        let mut output = vec![];
+
+        for expr in self.positional_iter().skip(starting_pos) {
+            let result = eval_constant(working_set, expr)?;
+            output.push(FromValue::from_value(&result)?);
+        }
+
+        Ok(output)
+    }
+
     fn opt<T: FromValue>(
         &self,
         engine_state: &EngineState,
@@ -107,6 +154,24 @@ impl CallExt for Call {
         }
     }
 
+    fn req_const<T: FromValue>(
+        &self,
+        working_set: &StateWorkingSet,
+        pos: usize,
+    ) -> Result<T, ShellError> {
+        if let Some(expr) = self.positional_nth(pos) {
+            let result = eval_constant(working_set, expr)?;
+            FromValue::from_value(&result)
+        } else if self.positional_len() == 0 {
+            Err(ShellError::AccessEmptyContent { span: self.head })
+        } else {
+            Err(ShellError::AccessBeyondEnd {
+                max_idx: self.positional_len() - 1,
+                span: self.head,
+            })
+        }
+    }
+
     fn req_parser_info<T: FromValue>(
         &self,
         engine_state: &EngineState,