From 5d6b26d98dc3466f0efa8843545971110be75953 Mon Sep 17 00:00:00 2001
From: Bahex <17417311+Bahex@users.noreply.github.com>
Date: Wed, 7 May 2025 18:26:39 +0300
Subject: [PATCH] feat(closure): closures that are const values

---
 crates/nu-protocol/src/eval_const.rs | 38 +++++++++++++++++++++++++---
 1 file changed, 34 insertions(+), 4 deletions(-)

diff --git a/crates/nu-protocol/src/eval_const.rs b/crates/nu-protocol/src/eval_const.rs
index b387de4120..e68828cfdd 100644
--- a/crates/nu-protocol/src/eval_const.rs
+++ b/crates/nu-protocol/src/eval_const.rs
@@ -5,8 +5,9 @@
 use crate::{
     ast::{Assignment, Block, Call, Expr, Expression, ExternalArgument},
     debugger::{DebugContext, WithoutDebug},
-    engine::{EngineState, StateWorkingSet},
+    engine::{Closure, EngineState, StateWorkingSet},
     eval_base::Eval,
+    ir::Instruction,
     record, BlockId, Config, HistoryFileFormat, PipelineData, Record, ShellError, Span, Value,
     VarId,
 };
@@ -548,12 +549,41 @@ impl Eval for EvalConst {
     }
 
     fn eval_row_condition_or_closure(
-        _: &StateWorkingSet,
+        state: &StateWorkingSet,
         _: &mut (),
-        _: BlockId,
+        block_id: BlockId,
         span: Span,
     ) -> Result<Value, ShellError> {
-        Err(ShellError::NotAConstant { span })
+        let block = state.get_block(block_id);
+        let ir_block = block
+            .ir_block
+            .as_ref()
+            .ok_or(ShellError::NotAConstant { span })?;
+
+        let non_const_var_idx = ir_block.instructions.iter().position(|ins| {
+            let Instruction::LoadVariable { var_id, .. } = ins else {
+                return false;
+            };
+            let var = state.get_variable(*var_id);
+            !(var.const_val.is_some()
+                || block
+                    .span
+                    .is_some_and(|b| b.contains_span(var.declaration_span)))
+        });
+
+        if let Some(idx) = non_const_var_idx {
+            Err(ShellError::NotAConstant {
+                span: ir_block.spans[idx],
+            })
+        } else {
+            Ok(Value::closure(
+                Closure {
+                    block_id,
+                    captures: vec![],
+                },
+                span,
+            ))
+        }
     }
 
     fn eval_overlay(_: &StateWorkingSet, span: Span) -> Result<Value, ShellError> {