From ad4fac015aae52e444e135969e8d144c43ae4533 Mon Sep 17 00:00:00 2001
From: robobun <117481402+robobun@users.noreply.github.com>
Date: Thu, 21 May 2026 20:17:52 +0000
Subject: [PATCH 1/2] shell_parser: drop stale capacity==1 debug_assert in
 parse_atom

BabyVec::with_capacity_in(1) routes through grow_to which floors the
allocation at 4 slots, so atoms.capacity() is never 1. The assertion
was a stack-fallback check carried over from the Zig port and does not
guard any invariant in the Rust implementation. Every single-atom parse
(e.g. `echo foo`) tripped it in debug builds since 303cd282b5
introduced BabyVec as the ArenaVec backing.
---
 src/shell_parser/parse.rs | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/src/shell_parser/parse.rs b/src/shell_parser/parse.rs
index 8ae38c01f92..0961042fb71 100644
--- a/src/shell_parser/parse.rs
+++ b/src/shell_parser/parse.rs
@@ -1915,10 +1915,7 @@ impl<'bump> Parser<'bump> {
 
         Ok(match atoms.len() {
             0 => None,
-            1 => {
-                debug_assert!(atoms.capacity() == 1);
-                Some(ast::Atom::new_simple(atoms.into_iter().next().unwrap()))
-            }
+            1 => Some(ast::Atom::new_simple(atoms.into_iter().next().unwrap())),
             _ => Some(ast::Atom::Compound(ast::CompoundAtom {
                 atoms: atoms.into_bump_slice(),
                 brace_expansion_hint: has_brace_open && has_brace_close && has_comma,

From f86c738b42c1d050c54dc05a2ffa1e86ffd697c5 Mon Sep 17 00:00:00 2001
From: robobun <117481402+robobun@users.noreply.github.com>
Date: Thu, 21 May 2026 20:20:30 +0000
Subject: [PATCH 2/2] test(shell): single-atom parse coverage (ls, echo ~)

---
 test/js/bun/shell/parse.test.ts | 36 +++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/test/js/bun/shell/parse.test.ts b/test/js/bun/shell/parse.test.ts
index a091858e9dc..2da7a674bc1 100644
--- a/test/js/bun/shell/parse.test.ts
+++ b/test/js/bun/shell/parse.test.ts
@@ -59,6 +59,42 @@ describe("parse shell", () => {
     expect(result).toEqual(expected);
   });
 
+  test("single atom", () => {
+    expect(JSON.parse(parse`ls`)).toEqual({
+      stmts: [
+        {
+          exprs: [
+            {
+              cmd: {
+                assigns: [],
+                name_and_args: [{ simple: { Text: "ls" } }],
+                redirect: redirect({}),
+                redirect_file: null,
+              },
+            },
+          ],
+        },
+      ],
+    });
+
+    expect(JSON.parse(parse`echo ~`)).toEqual({
+      stmts: [
+        {
+          exprs: [
+            {
+              cmd: {
+                assigns: [],
+                name_and_args: [{ simple: { Text: "echo" } }, { simple: { tilde: {} } }],
+                redirect: redirect({}),
+                redirect_file: null,
+              },
+            },
+          ],
+        },
+      ],
+    });
+  });
+
   test("compound atom", () => {
     const expected = {
       stmts: [