xai-org/x-algorithm · error · SemanticCheckFailure

block body cannot be empty

Error message

block body cannot be empty

What it means

A block expression `begin ... end` (or equivalent) must contain at least one statement; toBlock rejects empty blocks because there is no value to yield.

Source

Thrown at botmaker/src/java/com/twitter/botmaker/compiler/Compiler.java:1055

        throw new SemanticCheckFailure(
            String.format("Sort expects a collection of %s objects, but gets %s",
                Comparable.class.getName(),
                elementType)
        );
      }

      ASTNode result = Sort.toSort(exprText, collectionNode);
      return result;
    } else {
      throw new SemanticCheckFailure(String.format(
          "%s node with invalid number of children: %d", root.getText(), root.getChildCount()));
    }
  }

  private ASTNode toBlock(CompilerContext context, Tree root)
      throws ParseFailure, SemanticCheckFailure {
    if (root.getChildCount() == 0) {
      throw new SemanticCheckFailure("block body cannot be empty");
    }

    CompilerScope currentScope = context.addScope();
    ImmutableList.Builder<ASTNode> childrenBuilder = ImmutableList.builder();
    for (int i = 0; i < root.getChildCount(); i++) {
      childrenBuilder.add(createASTNodeTree(context, root.getChild(i)));
    }
    ImmutableList.Builder<Pair<String, Type>> variableListBuilder = ImmutableList.builder();
    for (Map.Entry<String, Parameter> entry : currentScope.getVariables().entrySet()) {
      variableListBuilder.add(Pair.of(entry.getKey(), entry.getValue().getReturnType()));
    }
    context.removeScope();
    return new Block(
        root.getText(),
        childrenBuilder.build(),
        variableListBuilder.build()
    );
  }

View on GitHub (pinned to 24c60942c5)

Solutions

1. Add at least one expression/statement to the block
2. If the block may legitimately be empty, guard generation so the whole block is omitted
3. Make the block end with the value you want it to evaluate to

Example fix

// before
begin end
// after
begin 0L end

if (blockStatements.isEmpty()) omitBlock(); // or insert a default value expression

catch (SemanticCheckFailure e) { if ("block body cannot be empty".equals(e.getMessage())) insertDefaultValue(); else throw e; }

When it happens

Trigger: Writing a block whose body is empty, usually because a template stripped out all statements or a conditional block was left blank after editing.

Common situations: Rule templates that omit optional sections, refactoring that deletes the last statement in a block, or code generation emitting `begin end` for empty inputs.

Related errors

• unrecognized function name:
• class to be imported has to be either a TBase or ThriftStruc
• cannot find class %s
• function passed to Foldl() returns %s but seed value is a %s
• Foldl1 is expected to return %s but passed function returns

AI-assisted analysis of xai-org/x-algorithm@24c60942c5 (2026-08-28). Data as JSON: /api/errors/40d31cda446f3c2b. Report an issue: GitHub.