Handle invalid shebang lines

src/error.rs

@@ -190,6 +190,10 @@ pub(crate) enum Error<'src> {
   Interrupted {
     signal: Signal,
   },
+  InvalidShebang {
+    recipe: Name<'src>,
+    shebang: String,
+  },
   ListInStringContext {
     context: StringContext<'src>,
     value: Value,
@@ -817,6 +821,9 @@ impl ColorDisplay for Error<'_> {
       Interrupted { signal } => {
         write!(f, "interrupted by {signal}")?;
       }
+      InvalidShebang { recipe, shebang } => {
+        write!(f, "recipe `{recipe}` has invalid shebang `{shebang}`")?;
+      }
       ListInStringContext { context, value, .. } => {
         write!(f, "list value {} {context}", value.color_display(color))?;
 

src/recipe.rs

@@ -494,14 +494,11 @@ impl<'src> Recipe<'src> {
           .unwrap_or_else(|| Interpreter::default_script_interpreter().clone()),
       )
     } else if self.body.first().is_some_and(Line::is_shebang) {
-      let line = evaluated_lines
-        .first()
-        .ok_or_else(|| Error::internal("evaluated_lines was empty"))?;
-
-      let shebang =
-        Shebang::new(line).ok_or_else(|| Error::internal(format!("bad shebang line: {line}")))?;
-
-      Executor::Shebang(shebang)
+      let shebang = &evaluated_lines[0];
+      Executor::Shebang(Shebang::new(shebang).ok_or_else(|| Error::InvalidShebang {
+        recipe: self.name,
+        shebang: shebang.into(),
+      })?)
     } else {
       Executor::Command(
         context

tests/shebang.rs

@@ -169,3 +169,17 @@ fn run_shebang() {
     .stderr("error: recipe `a` failed with exit code 200\n")
     .status(200);
 }
+
+#[test]
+fn invalid_shebang_error() {
+  Test::new()
+    .justfile(
+      "
+        foo:
+          #!{{ '' }}
+          echo bar
+      ",
+    )
+    .stderr_regex("error: recipe `foo` has invalid shebang `#!`\n")
+    .failure();
+}