feat(mongodb): add MongoDB Shell (mongosh) parser

Add ANTLR grammar for parsing MongoDB shell syntax with Go code generation.

Supported features:
- Shell commands: show dbs, show databases, show collections
- Database statements: db.collection.method(...) with method chains
- Collection access: dot notation, bracket notation, getCollection()
- Read methods: find(), findOne()
- Cursor modifiers: sort(), limit(), skip(), projection(), project()
- Helper functions as distinct AST nodes: ObjectId(), ISODate(), Date(),
  UUID(), Long(), NumberLong(), Int32(), NumberInt(), Double(),
  Decimal128(), NumberDecimal(), Timestamp(), RegExp()
- Document syntax: unquoted/quoted keys, nested documents, arrays,
  trailing commas
- Regex literals: /pattern/flags
- Literals: strings (single/double quoted), numbers, booleans, null
- Comments: line (//) and block (/* */)

The 'new' keyword is intentionally not supported for helper functions.
When users write 'new ObjectId()', the parser generates a helpful error
message using ANTLR's NotifyErrorListeners mechanism.

Also adds mongodb to the CI workflow parser list.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: h3n4l

.github/workflows/tests.yml

@@ -34,7 +34,7 @@ jobs:
         id: set-matrix
         run: |
           # List of all available parsers
-          ALL_PARSERS="redshift postgresql cql snowflake tsql doris starrocks trino plsql googlesql mysql partiql tidb mariadb cosmosdb"
+          ALL_PARSERS="redshift postgresql cql snowflake tsql doris starrocks trino plsql googlesql mysql partiql tidb mariadb cosmosdb mongodb"
           # Add more parsers here as they are added to the repository
           # ALL_PARSERS="redshift mysql postgresql"
 

mongodb/Makefile

@@ -0,0 +1,10 @@
+all: build test
+
+build:
+	@echo "Building MongoDB Shell parser..."
+	antlr -Dlanguage=Go -package mongodb -visitor -o . MongoShellLexer.g4 MongoShellParser.g4
+
+test:
+	go test -v -run TestMongoShellParser
+
+.PHONY: all build test

mongodb/MongoShellLexer.g4

@@ -0,0 +1,132 @@
+/*
+ * MongoDB Shell (mongosh) Lexer Grammar
+ * For use with ANTLR 4
+ */
+
+lexer grammar MongoShellLexer;
+
+// Keywords
+SHOW: 'show';
+DBS: 'dbs';
+DATABASES: 'databases';
+COLLECTIONS: 'collections';
+DB: 'db';
+NEW: 'new';
+TRUE: 'true';
+FALSE: 'false';
+NULL: 'null';
+GET_COLLECTION: 'getCollection';
+GET_COLLECTION_NAMES: 'getCollectionNames';
+
+// Helper function names (recognized as distinct tokens)
+OBJECT_ID: 'ObjectId';
+ISO_DATE: 'ISODate';
+DATE: 'Date';
+UUID: 'UUID';
+LONG: 'Long';
+NUMBER_LONG: 'NumberLong';
+INT32: 'Int32';
+NUMBER_INT: 'NumberInt';
+DOUBLE: 'Double';
+DECIMAL128: 'Decimal128';
+NUMBER_DECIMAL: 'NumberDecimal';
+TIMESTAMP: 'Timestamp';
+REG_EXP: 'RegExp';
+
+// Cursor modifiers (methods)
+FIND: 'find';
+FIND_ONE: 'findOne';
+SORT: 'sort';
+LIMIT: 'limit';
+SKIP_: 'skip';
+PROJECTION: 'projection';
+PROJECT: 'project';
+
+// Punctuation
+LPAREN: '(';
+RPAREN: ')';
+LBRACE: '{';
+RBRACE: '}';
+LBRACKET: '[';
+RBRACKET: ']';
+COLON: ':';
+COMMA: ',';
+DOT: '.';
+SEMI: ';';
+
+// Operators (for query operators like $gt, $lt, etc.)
+DOLLAR: '$';
+
+// Comments - must come before REGEX_LITERAL to properly capture /* ... */
+LINE_COMMENT
+    : '//' ~[\r\n]* -> channel(HIDDEN)
+    ;
+
+BLOCK_COMMENT
+    : '/*' .*? '*/' -> channel(HIDDEN)
+    ;
+
+// Regex literal
+REGEX_LITERAL
+    : '/' REGEX_BODY '/' REGEX_FLAGS?
+    ;
+
+fragment REGEX_BODY
+    : REGEX_CHAR+
+    ;
+
+fragment REGEX_CHAR
+    : ~[/\r\n\\]
+    | '\\' .
+    ;
+
+fragment REGEX_FLAGS
+    : [gimsuy]+
+    ;
+
+// Numbers
+NUMBER
+    : '-'? INT ('.' [0-9]+)? EXPONENT?
+    | '-'? '.' [0-9]+ EXPONENT?
+    ;
+
+fragment INT
+    : '0'
+    | [1-9] [0-9]*
+    ;
+
+fragment EXPONENT
+    : [eE] [+-]? [0-9]+
+    ;
+
+// Strings - both single and double quoted
+DOUBLE_QUOTED_STRING
+    : '"' (ESC | ~["\\])* '"'
+    ;
+
+SINGLE_QUOTED_STRING
+    : '\'' (ESC | ~['\\])* '\''
+    ;
+
+fragment ESC
+    : '\\' (["\\/bfnrt] | UNICODE | '\'')
+    ;
+
+fragment UNICODE
+    : 'u' HEX HEX HEX HEX
+    ;
+
+fragment HEX
+    : [0-9a-fA-F]
+    ;
+
+// Identifiers - for unquoted keys, collection names, method names
+// Allows $-prefixed identifiers for MongoDB operators like $gt, $in, etc.
+IDENTIFIER
+    : [$_a-zA-Z] [$_a-zA-Z0-9]*
+    ;
+
+// Whitespace
+WS
+    : [ \t\r\n]+ -> channel(HIDDEN)
+    ;