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Fixes #2637. Vertical_Bender.comp's INITIALIZE had a dangling if/else with no braces:
localG = coords_set(0, 0, 0);
ran unconditionally after the else, silently zeroing a correctly-computed gravity vector even when mcgravitation was true. This meant the component behaved as if gravity were always off, regardless of -g. Fix adds the missing braces so both statements are properly scoped to the else branch. One-line, behavior-only-changes-when-gravity-is-actually-enabled fix — verified to have zero effect on gravity-off simulations (bit-identical output before/after) and a real, expected effect once gravity is genuinely active inside the bender.

Declaration of use of AI-tools

• Please add a checkmark here if you used AI-tools during the work for this contribution

Used Claude (Anthropic) throughout: to trace the bug's root cause (identifying the dangling-else pattern and confirming its scope via the component's other mcgravitation checks), to trace its git history back to its introduction in 2017, and to benchmark its effect before/after the fix on a real instrument model. The fix itself is a two-character change (adding {/}).

Development OS / boundary conditions

macOS (Darwin). No special dependencies.

The identical fix was extensively tested via a separate instrument model (LOKI) using this component under McStas 3.5.42 / 3.7.24

PR Checklist for contributing to McStas/McXtrace

For a coherent and useful contribution to McStas/McXtrace, please fill in relevant parts of the checklist:

• My contribution includes patches to an existing component file

  • I have used the mcdoc utility and rendered a reasonable documentation page for the component (please attach as screenshot in comments!)
  • I have ensured that basic use of the component is OK (e.g. an instrument using it compiles?)
  • I have used the mctest utility to test one or more instruments making use of the component (please attach mcviewtest report as screenshot in comments)
  • I have used the mccode-clangformat tool to apply the standard McCode component indentation scheme
  • I have used the mcrun --c-lint "linter" and followed advice to remove most / all warnings that are raised

• My PR is meant to fix a specific, existing issue

  • I have indicated the issue number here: [BUG]: Vertical_Bender (contrib): dangling if/else silently disables gravity regardless of -g #2637
  • I have added documentation for the fix and possible side effects