Skip to main content

Invalid jump

Velox reports Invalid jump when a goto crosses into or out of a protected structured-statement region. The label can be declared and defined in the same procedure and still be an invalid target because entering or leaving that region would bypass compiler-managed control or cleanup state.

Example​

This jump enters a while body from outside the loop:

procedure ScriptEvent(var Value: Variant);
label
  InsideLoop;
begin
  goto InsideLoop; // Error: Invalid jump

  while Value <> '' do
  begin
  InsideLoop:
    Value := '';
  end;
end;

Keep control flow inside the structured statement, or replace the jump with a condition:

procedure ScriptEvent(var Value: Variant);
begin
  while Value <> '' do
    Value := '';
end;

How Velox detects it​

The modified PascalScript compiler records the bytecode range occupied by each supported structured region. After compiling the region, it compares every recorded label and goto in the current procedure:

  • a jump originating inside the range must target a label inside the same range; and
  • a jump originating outside the range must not target a label inside the range.

The check is applied to for, while and repeat bodies, case statements, with statements, and the bodies of try, except and finally. It is stricter than merely requiring the label and jump to be in the same procedure.

Correction procedure​

  1. Locate both the goto and its target label.
  2. Identify every loop, case, with or exception block that contains one but not the other.
  3. Move both points into the same region, or replace the jump with break, continue, exit, a Boolean flag or a helper procedure as appropriate.
  4. Recompile after correcting the earliest invalid boundary.

Edge cases and quirks​

  • A jump across a nested boundary is invalid even when the source indentation makes the target appear nearby.
  • The check works on compiled bytecode ranges, so the reported row can be at the end of the structured statement rather than at the original goto.
  • if bodies do not have their own explicit HasInvalidJumps range in the current compiler. Do not rely on that implementation detail to design control flow; another enclosing region can still reject the jump.
  • Velox recognises goto without Free Pascal's separate {$GOTO ON} switch. The Free Pascal page is compatibility guidance, not the Velox enablement rule.
  • Label '%s' not set - a declared label that has no definition.
  • Not in a loop - using break or continue without an active loop.
  • try..finally - cleanup semantics that a jump must not bypass.

External references​