migration-validator

name	migration-validator
description	Safety verification checklist for C-to-Rust migrations. Validates compilation, unsafe block minimization, memory safety, API compatibility, and idiomatic Rust patterns. Use when: validate migration, check Rust safety, verify converted code, migration QA.
license	MIT
metadata	{"version":"1.0.0","category":"validation","tags":["rust","migration","validation","safety","testing","quality-assurance"]}

Migration Validation Checklist

Compilation Check

• Rust code compiles with rustc --edition 2024
• No errors, only warnings acceptable if minor
• Clippy passes with 0 warnings (cargo clippy)

Safety Check

• Count unsafe blocks (target: 0 for easy/medium, minimize for hard)
• Every unsafe block has a // SAFETY: comment
• No raw pointer dereferences without bounds checking
• No transmute unless absolutely necessary
• No unwrap() on user-controlled data

Semantic Equivalence

• Same function signature (equivalent types)
• Same behavior for all valid inputs
• Same error conditions / edge cases
• Overflow behavior matches (wrapping vs. checked)
• Printf format matches exactly (especially %g → custom format_g())
• Bool/int distinction preserved (C int 0/1 ≠ Rust bool)

Differential Testing

• Compile C with cc -std=gnu11 -lm
• Compile Rust with rustc --edition 2024
• Run both with identical test inputs
• Compare outputs byte-by-byte (not just "looks similar")
• Test edge cases: empty input, max values, null/None, negative numbers
• Float tolerance: exact match preferred, tolerance only for known precision differences

Idiomatic Score

Enhanced formula with positive AND negative signals:

• Base: 100
• Negative: - (unsafe_blocks * 10) - (clippy_warnings * 2) - (unwrap_count * 3) - (as_casts * 1)
• Positive: + min(10, result_count * 2) + min(5, option_count) + min(5, iter_usage)
• Ranges: 90-100 Excellent, 70-89 Good, 60-69 Acceptable, <60 Needs repair

Quality Floor (P0)

• Track baseline unsafe count from initial translation
• NEVER allow repair to increase unsafe above baseline
• If repair adds unsafe → reject that iteration, try again
• This prevents the "oscillation" problem where repair trades quality for compilation

Best-Version Tracking (P1)

• Keep the version with highest score throughout repair loop
• If nothing passes validation, use best version as fallback (not raw c2rust)
• Prefer: compiling version > high-score non-compiling > c2rust fallback

Repair Loop Rules

• Effective iterations scale with file size:
  • <1000 LOC: full configured max (default 5)
  • 1000-2000 LOC: min(configured, 3)

  • 2000 LOC: min(configured, 2)

  • Chunked translations: max(configured, 8) — chunks are small, repair is affordable
• Stall detection: 2 unchanged error counts → re-translate at temp 0.7
• Temperature ramp: base 0.2 + 0.1 per iteration (capped at 1.0)
• Quality gate: if initial translation has >5 unsafe → re-translate at temp 0.5
• P5: Idiomatic hints — when compiles + diff passes but score < threshold, repair agent gets refactoring hints instead of empty feedback (prevents wasted iterations)

Validated Production Migrations

These fixtures are regression-tested and represent known-good migrations:

File	LOC C→Rust	Score	Unsafe	Notes
add, power, gcd, etc.	<50	100	0	Simple arithmetic
hash_table.c	204→~200	81	0	malloc/free → Box/Vec
cjson_combined.c	520→319	100	0	JSON parser, recursive data
expr_eval.c	1686→1446	100	0	74 functions, recursive descent
cjson_full_combined.c	1696→1439	100*	0	Full cJSON library (49/78 fns)
picohttpparser.c	1102→1551	100	0	HTTP parser, state machine
genann_combined.c	642→622	100	0	Neural network, fn ptrs→enum, autonomous pipeline
olive_combined.c	1443→1176	100	0	2D graphics, pixel buffers, checksum diff test
http_parser_combined.c	3680→1492	N/A	0	HTTP parser, goto state machine→line parsing, manual completion
miniz_core_standalone.c	4429	N/A	N/A	FallbackUnsafe (ceiling case)

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