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Catalyst Rules

Static performance analysis for Crystal. Detect allocation anti-patterns, algorithmic complexity issues, and resource leaks before they reach production.

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• Installation
• Usage
• catalyst --list-rules

Categories

Array & Enumerable (13 rules)

ID	Rule	Severity	Fix
CAT-001	sort.first → min/max	warning	✅
CAT-002	map{}.sum → sum{}	warning	✅
CAT-003	select + reject → partition	info	❌
CAT-004	Array#include? → Set	warning	❌
CAT-005	shift/unshift → Deque	info	❌
CAT-007	reverse.each → reverse_each	hint	✅
CAT-008	select.first/last → find	warning	✅
CAT-022	shuffle.first → sample	info	❌
CAT-033	select.map → single-pass	warning	❌
CAT-034	each_with_index.map → map_with_index	info	❌
CAT-046	reverse.reverse no-op	hint	❌
CAT-047	upcase/downcase no-op	hint	❌
CAT-048	puts to_s redundant	hint	❌

Hash (6 rules)

ID	Rule	Severity	Fix
CAT-006	hash.keys.each → each_key	info	✅
CAT-009	group_by → counter hash	info	❌
CAT-021	values.each → each_value	info	❌
CAT-024	keys/values.map → each_kv	info	❌
CAT-030	keys.includes? → has_key?	info	❌
CAT-031	values.includes? → has_value?	info	❌

String (9 rules)

ID	Rule	Severity	Fix
CAT-010	String#+ in loop → String.build	warning	❌
CAT-011	Multi-pass gsub	hint	❌
CAT-018	downcase == → compare	hint	✅
CAT-023	includes? → char comparison	info	❌
CAT-032	split.first → split_limit	info	❌
CAT-035	split("") → each_char	hint	❌
CAT-036	chars.each → each_char	info	❌
CAT-039	Regex.new → constant	warning	❌
CAT-040	String.build for literals	hint	❌

Resource & IO (8 rules)

ID	Rule	Severity	Fix
CAT-013	TCPSocket leak	error	❌
CAT-014	File.read → streaming	info	✅
CAT-020	IO::Memory → pipe	warning	✅
CAT-025	File.open leak	error	❌
CAT-026	Dir.open leak	error	❌
CAT-027	Tempfile leak	error	❌
CAT-028	HTTP::Client leak	error	❌
CAT-029	DB.open leak	error	❌

Type & Serialization (4 rules)

ID	Rule	Severity	Fix
CAT-012	JSON.parse → Serializable	info	❌
CAT-015	Struct vs Class	info	❌
CAT-016	Large union types	info	❌
CAT-019	Regex.new in loop	warning	✅

Performance & Idiom (9 rules)

ID	Rule	Severity	Fix
CAT-017	Time.local → Time.utc	hint	✅
CAT-037	Logging block form	info	❌
CAT-038	Capacity hints	info	❌
CAT-041	Parse → constant	hint	❌
CAT-042	sleep(0) → Fiber.yield	hint	❌
CAT-043	Random.new reuse	info	❌
CAT-044	** → Math.pow	info	❌
CAT-049	Thread.new → spawn	warning	❌
CAT-050	Fiber.new → spawn	warning	❌

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Total: 49 rules | catalyst --list-rules