Add RapidCheck property-based tests that find real DuckDB bugs

[peterxcli]

What is this?

A property-based test harness for DuckDB using RapidCheck (the C++ equivalent of Rust's proptest), inspired by apache/arrow-rs#10352.

Instead of fixed inputs, each test states a property and RapidCheck runs it against hundreds of randomly generated inputs, shrinking any failure to a minimal counterexample:

• round trips — any value must survive CAST(v AS VARCHAR) -> CAST(back AS T), Value::ToSQLString() -> re-parse, to_json -> cast back, INSERT -> SELECT, and write -> CHECKPOINT -> reopen for every force_compression setting
• oracles — LIKE/ILIKE vs a 40-line reference matcher; substring/split/pad/trim/translate/levenshtein vs reference implementations; integer/HUGEINT/DECIMAL arithmetic must error exactly when the __int128 result is out of range; date parts vs independent civil-calendar algorithms
• consistency — constant vs parameterized paths, list_sort vs ORDER BY, list_contains vs list_position

The core piece is test/property/generators.cpp: random LogicalTypes (including nested STRUCT/LIST/ARRAY/MAP/UNION/ENUM) and random Values of any type, seeded with adversarial special cases (NaN/-0.0/denormals, NUL bytes, combining marks, quotes/braces in strings, extreme dates/timestamps/intervals, decimal width/scale limits).

How to build

# 1. build DuckDB with assertions + ASAN/UBSAN (best build for bug hunting)
GEN=ninja CORE_EXTENSIONS='json' make relassert

# 2. build the property tests (standalone project; links against the build above,
#    so iterating on tests never rebuilds DuckDB; RapidCheck is fetched via FetchContent)
cmake -S test/property -B build/property -G Ninja -DDUCKDB_BUILD_DIR=$PWD/build/relassert
cmake --build build/property

How to run / how to find bugs

# run everything (100 cases per property by default)
build/property/property_test "[property]"

# crank up iterations for a hunting session; noshrink=1 surveys failures fast
# (shrinking large nested counterexamples re-runs a query per shrink step)
RC_PARAMS="max_success=1000 max_size=45 noshrink=1" build/property/property_test "[property]"

# one suite: [roundtrip] [strings] [lists] [arithmetic] [datetime] [storage]
build/property/property_test "[strings]"

# reproduce a failure deterministically (RapidCheck prints the seed of every run)
RC_PARAMS="seed=4570269180443172881" build/property/property_test "VARCHAR cast round trip"

When a property fails you get the shrunk counterexample plus the exact value/SQL/error, e.g.:

Falsifiable after 981 tests and 7 shrinks
Round trip through VARCHAR failed
  original: TIME WITH TIME ZONE[][]: [['00:00:00-05:59']] timetz_bits=75658
  back:     TIME WITH TIME ZONE[][]: [['00:00:00-05:59']] timetz_bits=79139

…which is how the TIMETZ formatting bug below was found (two different offsets printing identically).

Bugs found so far

Full write-up with minimal reproductions in test/property/FINDINGS.md. Verified on v1.6.0-dev13151:

1. SELECT last_day(DATE '5881580-07-10') throws an INTERNAL error that invalidates the whole database — last_day computes first-of-next-month (out of range) and is not marked SetFallible()
2. date_trunc('week'/'isoyear', DATE '5877642-06-25 (BC)') — signed integer overflow (UB) in date_t::operator- (date.hpp:58); aborts under UBSan
3. TIMETZ offsets with zero minutes but nonzero seconds print incorrectly: '12:00:00-05:00:59'::TIMETZ prints 12:00:00-05:59 (a different offset)
4. list_sort([INTERVAL '31 days', INTERVAL '1 month']) returns [31 days, 1 month] although 31 days > 1 month is true and ORDER BY sorts the other way — create_sort_key skips interval normalization
5. Value::ToSQLString() doesn't escape quotes in STRUCT keys, renders BIT values bare (re-parse as INTEGER), and loses UNION member types
6. INTERVAL text asymmetry: to_microseconds(9223372036854775807)::VARCHAR prints 10-digit hours that the interval parser (9-digit limit) cannot read back
7. list_contains([false,true,NULL], NULL) returns NULL but list_position(...) returns 3 — the twin functions disagree on NULL semantics
8. weekofyear/isoyear/date_trunc fail with "Date out of range" on minimum-year dates whose result is representable
9. Sort internally round-trips column types through SQL strings (Sort::Sort -> DecodeSortKeyBind), which breaks for API-created types with unparseable string forms (e.g. ENUM values containing NUL, possible via Arrow dictionaries)
10. '883406386745030.3'::JSON::DECIMAL(16,1) -> 883406386745030.2 (JSON -> DECIMAL goes through a double)
11. (-32768)::SMALLINT % (-1)::SMALLINT errors ("Overflow in division") where PostgreSQL returns 0
12. levenshtein/damerau_levenshtein/hamming count bytes, not characters, for multi-byte UTF-8

Each known bug is fenced off in the tests with an RC_PRE guard marked KNOWN ISSUE, so the suite is fully green (12 test cases / 35 properties at 1000 iterations each) and keeps hunting for new bugs rather than rediscovering these.

Files

file	contents
test/property/README.md	build/run/extend docs
test/property/FINDINGS.md	the bug list with repros
test/property/CMakeLists.txt	standalone project, -DDUCKDB_BUILD_DIR=...
test/property/include/property_test.hpp	PropDB helpers, value comparison, assertion macros
test/property/generators.cpp	random types + values for any DuckDB type
test/property/test_*.cpp	the six property suites

🤖 Generated with Claude Code

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Compute generated range endpoints in int128

When large steps cross zero, the mathematical endpoint fits in BIGINT even though the intermediate multiplication does not. For example, start = INT64_MIN, stop = INT64_MAX, and step = INT64_MAX produce range_count == 3, but this line evaluates 2 * INT64_MAX in int64_t; the default UBSan build therefore aborts inside the oracle, while an unsanitized build can report a false endpoint mismatch. Keep the endpoint calculation in __int128 until after the addition and checked conversion.

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[chatgpt-codex-connector]

Pin RapidCheck to an immutable revision

When RAPIDCHECK_SOURCE_DIR is not supplied, every clean configuration fetches whatever commit master references at that moment. An upstream API change, force-push, or regression can consequently make the same DuckDB commit stop building or change its property-generation behavior without any repository change. Use a specific commit or release tag so the test harness remains reproducible.

Useful? React with 👍 / 👎.