[RULE] Rule G025: Flag Post-Decrement Loop Indexing Patterns

[mijinummi]

Labels: medium-difficulty, gasguard-rules, ast, gasguard
Difficulty: Medium
Module: rules/g025_loop_decrement.rs

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🧠 Concept

Implement static rule G025 to detect loop structures that use post-decrement operators (i--) instead of pre-decrement operators (--i).

⚠️ Problem

Post-decrement operations (i--) copy original values to stack locations before applying decrements, creating redundant stack manipulation instructions compared to --i.

📁 Implementation Scope

• rules/g025_loop_decrement.rs
• test/fixtures/g025_samples.sol

🛠️ Requirements

1. Analyze loop step statements in AST loop nodes.
2. Identify post-decrement expressions on loop counter variables.
3. Emit recommendation to replace post-decrement (i--) with pre-decrement (--i).

🎯 Acceptance Criteria

• Flags post-decrement loop counter expressions accurately.
• Passes without warnings on pre-decrement loop statements.

[Francis6-git]

My approach:
I’ll implement G025 by analyzing loop step expressions in the Solidity AST and detecting post-decrement (i--) operations on loop counters.

I’ll add fixture cases covering valid detections, pre-decrement (--i) cases, and non-loop decrements, then verify the rule reports only the intended patterns and passes the existing test suite.