ClickHouse/utils/grammar-fuzzer/README.md

How to use Fuzzer

The fuzzer consists of auto-generated files:

ClickHouseUnlexer.py
ClickHouseUnparser.py

They are generated from grammar files (.g4) using Grammarinator:

pip3 install grammarinator
grammarinator-process ClickHouseLexer.g4 ClickHouseParser.g4 -o fuzzer/

Then you can generate test input for ClickHouse client:

cd fuzzer
grammarinator-generate \
  -r query_list                                               \ # top-level rule
  -o /tmp/sql_test_%d.sql                                     \ # template for output test names
  -n 10                                                       \ # number of tests
  -c 0.3                                                      \
  -d 20                                                       \ # depth of recursion
  -p ClickHouseUnparser.py -l ClickHouseUnlexer.py            \ # auto-generated unparser and unlexer
  --test-transformers SpaceTransformer.single_line_whitespace \ # transform function to insert whitespace

For more details see grammarinator-generate --help. As a test-transformer function also can be used SpaceTransformer.multi_line_transformer - both functions reside in fuzzer/SpaceTransformer.py file.

Parsing steps

1. Replace all operators with corresponding functions.
2. Replace all asterisks with columns - if it's inside function call, then expand it as multiple arguments. Warn about undeterministic invocations when functions have positional arguments.

Old vs. new parser

• a as b [c] - accessing aliased array expression is not possible.
• a as b . 1 - accessing aliased tuple expression is not possible.
• between a is not null and b - between operator should have lower priority than is null.
• *.1 - accessing asterisk tuple expression is not possible.