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.