Fix ladder diagram execution order in generated ST code

[devin-ai-integration]

Fix ladder diagram execution order in generated ST code

Summary

Fixes a critical bug where ladder diagram rungs were being executed out of order in generated Structured Text programs. The issue affected projects where blocks without explicit executionOrderId were sorted by position, causing incorrect top-to-bottom execution sequence.

Root cause: Two bugs in the sorting logic:

1. SortInstances() used operator.eq() which returns booleans, but cmp_to_key() requires integer comparisons (-1/0/1)
2. ComputeProgram() sorted outVariables&coils and blocks separately then concatenated them, always placing coils before blocks regardless of Y-position

Fix: Changed to use integer subtraction for proper comparison and combine all unordered instances before sorting by Y-coordinate.

Impact: Blocks now execute in correct top-to-bottom order based on their visual position in the ladder diagram.

Review & Testing Checklist for Human

• Test with multiple PLCopen XML projects - especially ones with complex ladder diagrams, mixed block types, and varying Y-coordinates to ensure no regressions
• Verify Y-coordinate sorting logic - confirm the 10-pixel tolerance for "same rung" detection works correctly with your typical ladder diagram layouts
• Test mixed executionOrderId scenarios - projects with some blocks having explicit executionOrderId > 0 and others relying on position-based sorting
• End-to-end execution testing - deploy generated ST code to actual PLC hardware/simulator to verify execution order is correct and no functional regressions occurred

Notes

• Only tested with the specific plc.xml file provided by the user - broader testing needed to catch edge cases
• This change affects ALL ladder diagram and function block diagram projects, so thorough regression testing is critical
• The fix maintains existing behavior for SFC (Sequential Function Chart) and explicit executionOrderId cases

Link to Devin run: https://app.devin.ai/sessions/c3ee655cdb0f4f7ab869c1554723a288
Requested by: Thiago Alves (@thiagoralves)

[devin-ai-integration]

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[Copilot]

Pull Request Overview

This PR fixes a critical bug in the PLCopen compiler where ladder diagram rungs were executing out of order in generated Structured Text code. The issue stemmed from incorrect comparison functions and improper sorting of different instance types.

Key changes:

• Fixed comparison function to return integers instead of booleans for proper sorting
• Combined all unordered instances before sorting to maintain correct Y-coordinate order
• Removed unused operator import

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