We keep it in this repository for your curiosity. But this is not the parser of ClickHouse.

Grammar is located inside ClickHouseLexer.g4 and ClickHouseParser.g4 files.

To generate source code you need to install locally the antlr4 binary:

cd src/Parsers/New
antlr4 -no-listener -visitor -package DB -Dlanguage=Cpp ClickHouseLexer.g4  # if you have changes in a lexer part of grammar
antlr4 -no-listener -visitor -package DB -Dlanguage=Cpp ClickHouseParser.g4

Commit only git-tracked generated files - not all of the generated content is required.