ANTLR grammar fails to parse tabular subquery on the right of in

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#194 opened on Aug 19, 2026 3 comments 0 reactions 0 assignees View on GitHub

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Assessment

Difficulty: 3/5
Estimated time: 1-2 days
Newbie friendliness: 72/100

Issue type: Bug
Clarity: Mostly clear
Activity status: Active
Tech stack: java, python
Domain: compilers

Research direction

Start with the listEqualityExpression rule in Kql.g4 and reproduce the failure using the provided Java ANTLR generation command and Python parser example. Update the grammar so the tabular subquery form parses while preserving the comma-separated invocation form, then rerun the full KQL example and confirm it produces no parse errors.

Written by the indexing model from the issue text.

Description

The KQL docs mention that this is a valid expression:

StormEvents 
| where State in (
    StormEvents
    | summarize count() by State
    | top 5 by count_
    ) 
| count

https://learn.microsoft.com/en-us/kusto/query/in-cs-operator?view=azure-data-explorer#tabular-expression

The KQL ANTLR grammar in the repo fails to parse it:

line 5:4 mismatched input '|' expecting {')', ','}
line 7:4 mismatched input ')' expecting {<EOF>, ';'}

This seems to be due to this line in Kql.g4:

listEqualityExpression:
    Left=relationalExpression OperatorToken=(IN | NOT_IN | IN_CI | NOT_IN_CI | HAS_ANY | HAS_ALL) '(' Expressions+=invocationExpression (',' Expressions+=invocationExpression)* ')';

which may need to be replaced with something like this (extra pipeExpression):

listEqualityExpression:
      Left=relationalExpression OperatorToken=(IN | NOT_IN | IN_CI | NOT_IN_CI | HAS_ANY | HAS_ALL) '(' Subquery=pipeExpression ')'
    | Left=relationalExpression OperatorToken=(IN | NOT_IN | IN_CI | NOT_IN_CI | HAS_ANY | HAS_ALL) '(' Expressions+=invocationExpression (',' Expressions+=invocationExpression)* ')'
    ;

Full repro:

Install Java 11: https://learn.microsoft.com/en-us/java/openjdk/download
Install Python 3.14 https://www.python.org/downloads/
Run pip install antlr4-python3-runtime==4.13.2
Download https://repo1.maven.org/maven2/org/antlr/antlr4/4.13.2/antlr4-4.13.2-complete.jar
Run java -jar antlr4-4.13.2-complete.jar -Dlanguage=Python3 -visitor -o out Kql.g4

Use the Python KQL parser:

from antlr4 import InputStream, CommonTokenStream
from KqlLexer import KqlLexer
from KqlParser import KqlParser

def parse(query: str):
    parser = KqlParser(CommonTokenStream(KqlLexer(InputStream(query))))
    tree = parser.top()
    print(tree.toStringTree(recog=parser))

parse('''
StormEvents 
| where State in (
    StormEvents
    | summarize count() by State
    | top 5 by count_
    ) 
| count
''')

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