From 1f06f8405c8e2553574a8327944894722e147b9d Mon Sep 17 00:00:00 2001
From: Horasal <1991933+horasal@users.noreply.github.com>
Date: Mon, 28 Aug 2023 20:38:11 +0900
Subject: [PATCH] handle empty pipeline while parsing let (fix Issue10083)
 (#10116)

- fixes #10083

# Description

nushell crashes in the following 2 condition:

- `let a = {}` , then delete `{`
- `let a = | {}`, then delete `{`

When delete `{` the pipeline becomes empty but current `nu-parser`
assume they are non-empty. This pr adds extra empty check to avoid
crash.


Co-authored-by: Horasal <horsal@horsal.dev>
---
 crates/nu-parser/src/parser.rs        | 21 ++++++++++++++-------
 crates/nu-parser/tests/test_parser.rs | 12 ++++++++++++
 2 files changed, 26 insertions(+), 7 deletions(-)

diff --git a/crates/nu-parser/src/parser.rs b/crates/nu-parser/src/parser.rs
index 85a510f9b1..ae1bb6a048 100644
--- a/crates/nu-parser/src/parser.rs
+++ b/crates/nu-parser/src/parser.rs
@@ -5476,10 +5476,14 @@ pub fn parse_pipeline(
                                         {
                                             let block = working_set.get_block(*block_id);
 
-                                            let element = block.pipelines[0].elements[0].clone();
-
-                                            if let PipelineElement::Expression(prepend, expr) =
-                                                element
+                                            if let Some(PipelineElement::Expression(
+                                                prepend,
+                                                expr,
+                                            )) = block
+                                                .pipelines
+                                                .first()
+                                                .and_then(|p| p.elements.first())
+                                                .cloned()
                                             {
                                                 if expr.has_in_variable(working_set) {
                                                     let new_expr = PipelineElement::Expression(
@@ -5608,9 +5612,12 @@ pub fn parse_pipeline(
                                 {
                                     let block = working_set.get_block(*block_id);
 
-                                    let element = block.pipelines[0].elements[0].clone();
-
-                                    if let PipelineElement::Expression(prepend, expr) = element {
+                                    if let Some(PipelineElement::Expression(prepend, expr)) = block
+                                        .pipelines
+                                        .first()
+                                        .and_then(|p| p.elements.first())
+                                        .cloned()
+                                    {
                                         if expr.has_in_variable(working_set) {
                                             let new_expr = PipelineElement::Expression(
                                                 prepend,
diff --git a/crates/nu-parser/tests/test_parser.rs b/crates/nu-parser/tests/test_parser.rs
index e6647e37d5..8278f702ab 100644
--- a/crates/nu-parser/tests/test_parser.rs
+++ b/crates/nu-parser/tests/test_parser.rs
@@ -1007,6 +1007,18 @@ mod string {
     }
 }
 
+#[rstest]
+#[case(b"let a = }")]
+#[case(b"mut a = }")]
+#[case(b"let a = | }")]
+#[case(b"mut a = | }")]
+fn test_semi_open_brace(#[case] phrase: &[u8]) {
+    let engine_state = EngineState::new();
+    let mut working_set = StateWorkingSet::new(&engine_state);
+    // this should not panic
+    let _block = parse(&mut working_set, None, phrase, true);
+}
+
 mod range {
     use super::*;
     use nu_protocol::ast::{RangeInclusion, RangeOperator};