Recursively export constants from modules (#10049)

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# Description
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https://github.com/nushell/nushell/pull/9773 introduced constants to
modules and allowed to export them, but only within one level. This PR:
* allows recursive exporting of constants from all submodules
* fixes submodule imports in a list import pattern
* makes sure exported constants are actual constants

Should unblock https://github.com/nushell/nushell/pull/9678

### Example:
```nushell
module spam {
    export module eggs {
        export module bacon {
            export const viking = 'eats'
        }
    }
}

use spam 
print $spam.eggs.bacon.viking  # prints 'eats'

use spam [eggs]
print $eggs.bacon.viking  # prints 'eats'

use spam eggs bacon viking
print $viking  # prints 'eats'
```

### Limitation 1:

Considering the above `spam` module, attempting to get `eggs bacon` from
`spam` module doesn't work directly:
```nushell
use spam [ eggs bacon ]  # attempts to load `eggs`, then `bacon`
use spam [ "eggs bacon" ]  # obviously wrong name for a constant, but doesn't work also for commands
```

Workaround (for example):
```nushell
use spam eggs
use eggs [ bacon ]

print $bacon.viking  # prints 'eats'
```

I'm thinking I'll just leave it in, as you can easily work around this.
It is also a limitation of the import pattern in general, not just
constants.

### Limitation 2:

`overlay use` successfully imports the constants, but `overlay hide`
does not hide them, even though it seems to hide normal variables
successfully. This needs more investigation.

# User-Facing Changes
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helps us keep track of breaking changes. -->

Allows recursive constant exports from submodules.

# Tests + Formatting
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crates/nu-cmd-lang/src/core_commands/overlay/use_.rs

@@ -68,7 +68,7 @@ impl Command for OverlayUse {
 
         let maybe_origin_module_id =
             if let Some(overlay_expr) = call.get_parser_info("overlay_expr") {
-                if let Expr::Overlay(module_id) = overlay_expr.expr {
+                if let Expr::Overlay(module_id) = &overlay_expr.expr {
                     module_id
                 } else {
                     return Err(ShellError::NushellFailedSpanned {
@@ -106,11 +106,11 @@ impl Command for OverlayUse {
         };
 
         if let Some(module_id) = maybe_origin_module_id {
-            // Add environment variables only if:
+            // Add environment variables only if (determined by parser):
             // a) adding a new overlay
             // b) refreshing an active overlay (the origin module changed)
 
-            let module = engine_state.get_module(module_id);
+            let module = engine_state.get_module(*module_id);
 
             // Evaluate the export-env block (if any) and keep its environment
             if let Some(block_id) = module.env_block {
@@ -122,7 +122,7 @@ impl Command for OverlayUse {
                 )?;
 
                 let block = engine_state.get_block(block_id);
-                let mut callee_stack = caller_stack.gather_captures(&block.captures);
+                let mut callee_stack = caller_stack.gather_captures(engine_state, &block.captures);
 
                 if let Some(path) = &maybe_path {
                     // Set the currently evaluated directory, if the argument is a valid path

crates/nu-cmd-lang/src/core_commands/use_.rs

@@ -1,8 +1,8 @@
 use nu_engine::{eval_block, find_in_dirs_env, get_dirs_var_from_call, redirect_env};
-use nu_protocol::ast::{Call, Expr, Expression, ImportPattern, ImportPatternMember};
+use nu_protocol::ast::{Call, Expr, Expression};
 use nu_protocol::engine::{Command, EngineState, Stack};
 use nu_protocol::{
-    Category, Example, Module, PipelineData, ShellError, Signature, Span, SyntaxShape, Type, Value,
+    Category, Example, PipelineData, ShellError, Signature, SyntaxShape, Type, Value,
 };
 
 #[derive(Clone)]
@@ -63,9 +63,24 @@ This command is a parser keyword. For details, check:
         };
 
         if let Some(module_id) = import_pattern.head.id {
-            let module = engine_state.get_module(module_id);
+            // Add constants
+            for var_id in &import_pattern.constants {
+                let var = engine_state.get_var(*var_id);
+
+                if let Some(constval) = &var.const_val {
+                    caller_stack.add_var(*var_id, constval.clone());
+                } else {
+                    return Err(ShellError::NushellFailedSpanned {
+                        msg: "Missing Constant".to_string(),
+                        label: "constant not added by the parser".to_string(),
+                        span: var.declaration_span,
+                    });
+                }
+            }
 
             // Evaluate the export-env block if there is one
+            let module = engine_state.get_module(module_id);
+
             if let Some(block_id) = module.env_block {
                 let block = engine_state.get_block(block_id);
 
@@ -84,7 +99,7 @@ This command is a parser keyword. For details, check:
                     .as_ref()
                     .and_then(|path| path.parent().map(|p| p.to_path_buf()));
 
-                let mut callee_stack = caller_stack.gather_captures(&block.captures);
+                let mut callee_stack = caller_stack.gather_captures(engine_state, &block.captures);
 
                 // If so, set the currently evaluated directory (file-relative PWD)
                 if let Some(parent) = maybe_parent {
@@ -110,14 +125,6 @@ This command is a parser keyword. For details, check:
                 // Merge the block's environment to the current stack
                 redirect_env(engine_state, caller_stack, &callee_stack);
             }
-
-            use_variables(
-                engine_state,
-                import_pattern,
-                module,
-                caller_stack,
-                call.head,
-            );
         } else {
             return Err(ShellError::GenericError(
                 format!(
@@ -170,76 +177,6 @@ This command is a parser keyword. For details, check:
     }
 }
 
-fn use_variables(
-    engine_state: &EngineState,
-    import_pattern: &ImportPattern,
-    module: &Module,
-    caller_stack: &mut Stack,
-    head_span: Span,
-) {
-    if !module.variables.is_empty() {
-        if import_pattern.members.is_empty() {
-            // add a record variable.
-            if let Some(var_id) = import_pattern.module_name_var_id {
-                let mut cols = vec![];
-                let mut vals = vec![];
-                for (var_name, var_id) in module.variables.iter() {
-                    if let Some(val) = engine_state.get_var(*var_id).clone().const_val {
-                        cols.push(String::from_utf8_lossy(var_name).to_string());
-                        vals.push(val)
-                    }
-                }
-                caller_stack.add_var(
-                    var_id,
-                    Value::record(cols, vals, module.span.unwrap_or(head_span)),
-                )
-            }
-        } else {
-            let mut have_glob = false;
-            for m in &import_pattern.members {
-                if matches!(m, ImportPatternMember::Glob { .. }) {
-                    have_glob = true;
-                    break;
-                }
-            }
-            if have_glob {
-                // bring all variables into scope directly.
-                for (_, var_id) in module.variables.iter() {
-                    if let Some(val) = engine_state.get_var(*var_id).clone().const_val {
-                        caller_stack.add_var(*var_id, val);
-                    }
-                }
-            } else {
-                let mut members = vec![];
-                for m in &import_pattern.members {
-                    match m {
-                        ImportPatternMember::List { names, .. } => {
-                            for (n, _) in names {
-                                if module.variables.contains_key(n) {
-                                    members.push(n);
-                                }
-                            }
-                        }
-                        ImportPatternMember::Name { name, .. } => {
-                            if module.variables.contains_key(name) {
-                                members.push(name)
-                            }
-                        }
-                        ImportPatternMember::Glob { .. } => continue,
-                    }
-                }
-                for m in members {
-                    if let Some(var_id) = module.variables.get(m) {
-                        if let Some(val) = engine_state.get_var(*var_id).clone().const_val {
-                            caller_stack.add_var(*var_id, val);
-                        }
-                    }
-                }
-            }
-        }
-    }
-}
-
 #[cfg(test)]
 mod test {
     #[test]