From d27a55267b8a5fb2b9c5bcfb5378e5b3f2aa3dce Mon Sep 17 00:00:00 2001
From: m0g3r <87276771+m0g3r@users.noreply.github.com>
Date: Thu, 13 Aug 2026 00:09:15 +0200
Subject: [PATCH] Fix panic compiling an empty component with debug info

generate_simulated_dwarf unwrapped the first core-module translation to
name its compilation unit, but a component with no core modules has no
translations, so `wasmtime compile -D debug-info=y` panicked on a valid
`(component)` input. Return early instead: with no translations there are
no functions to describe.
---
 .../cranelift/src/debug/transform/simulate.rs  |  9 ++++++++-
 tests/all/cli_tests.rs                         | 18 ++++++++++++++++++
 tests/all/cli_tests/empty_component.wat        |  1 +
 3 files changed, 27 insertions(+), 1 deletion(-)
 create mode 100644 tests/all/cli_tests/empty_component.wat

diff --git a/crates/cranelift/src/debug/transform/simulate.rs b/crates/cranelift/src/debug/transform/simulate.rs
index dd39c2f54398..2504ea32653a 100644
--- a/crates/cranelift/src/debug/transform/simulate.rs
+++ b/crates/cranelift/src/debug/transform/simulate.rs
@@ -296,8 +296,15 @@ pub fn generate_simulated_dwarf(
     out_strings: &mut write::StringTable,
     isa: &dyn TargetIsa,
 ) -> Result<(), Error> {
+    // A component without any core modules has no functions to describe, and
+    // the compilation unit below names itself after the first translation's
+    // wasm file. There is nothing to simulate, so leave the DWARF empty.
+    let Some((_, first_translation)) = compilation.translations.iter().next() else {
+        return Ok(());
+    };
+
     let (wasm_file, path) = {
-        let di = &compilation.translations.iter().next().unwrap().1.debuginfo;
+        let di = &first_translation.debuginfo;
         let path = di
             .wasm_file
             .path
diff --git a/tests/all/cli_tests.rs b/tests/all/cli_tests.rs
index 8f175b7077d8..9c2b8e9b208e 100644
--- a/tests/all/cli_tests.rs
+++ b/tests/all/cli_tests.rs
@@ -3716,3 +3716,21 @@ fn non_utf8_raises_error() -> Result<()> {
     }
     Ok(())
 }
+
+#[test]
+fn compile_empty_component_with_debug_info() -> Result<()> {
+    // A component with no core modules reached simulated-DWARF generation with
+    // nothing to describe, which used to panic instead of compiling.
+    let td = TempDir::new()?;
+    let cwasm = td.path().join("empty-component.cwasm");
+    let stdout = run_wasmtime(&[
+        "compile",
+        "-D",
+        "debug-info=y",
+        "tests/all/cli_tests/empty_component.wat",
+        "-o",
+        cwasm.to_str().unwrap(),
+    ])?;
+    assert_eq!(stdout, "");
+    Ok(())
+}
diff --git a/tests/all/cli_tests/empty_component.wat b/tests/all/cli_tests/empty_component.wat
new file mode 100644
index 000000000000..e5627d1d0fc7
--- /dev/null
+++ b/tests/all/cli_tests/empty_component.wat
@@ -0,0 +1 @@
+(component)