fix(tvix/eval): skip runtime completely on compiler errors

This branch was missing, and an assumption elsewhere just executed the
returned (broken) bytecode.

This fixes b/253.

Change-Id: I015023ba921bc08ea03882167f1f560feca25e50
Reviewed-on: https://cl.tvl.fyi/c/depot/+/8090
Tested-by: BuildkiteCI
Reviewed-by: flokli <flokli@flokli.de>
Autosubmit: tazjin <tazjin@tvl.su>

tvix/eval/src/lib.rs

@@ -317,6 +317,12 @@ fn parse_compile_internal(
     result.warnings = compiler_result.warnings;
     result.errors.extend(compiler_result.errors);
 
+    // Short-circuit if errors exist at this point (do not pass broken
+    // bytecode to the runtime).
+    if !result.errors.is_empty() {
+        return None;
+    }
+
     // Return the lambda (for execution) and the globals map (to
     // ensure the invariant that the globals outlive the runtime).
     Some((compiler_result.lambda, compiler_result.globals))

tvix/eval/src/tests/one_offs.rs

@@ -22,3 +22,15 @@ fn test_source_builtin() {
         value,
     );
 }
+
+#[test]
+fn skip_broken_bytecode() {
+    let result = Evaluation::new(/* code = */ "x", None).evaluate();
+
+    assert_eq!(result.errors.len(), 1);
+
+    assert!(matches!(
+        result.errors[0].kind,
+        ErrorKind::UnknownStaticVariable
+    ));
+}