Drools Rule Checker — IntelliJ IDEA Plugin for DRL Files

Full language support for Drools Rule Language (.drl) files in IntelliJ IDEA — grammar-based parsing, context-aware code completion, go-to-definition, real-time validation, quick fixes, and more.

The most comprehensive Drools IDE plugin available. Write Drools rules with the same level of intelligent assistance you get for Java.

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Why Drools Rule Checker?

If you write Drools rules in IntelliJ IDEA, you've probably noticed there's no built-in support for .drl files. No syntax highlighting, no completion, no error checking. This plugin fixes that.

Drools Rule Checker gives you:

• A proper grammar-based parser that understands DRL structure
• Code completion that knows your project's classes, methods, and fields
• Go-to-definition — Ctrl+Click on class names to jump to Java source
• Real-time validation — see errors as you type, not at deploy time
• Quick fixes — one-click solutions for common problems

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Features

Grammar-Based Parser with Error Recovery

Built on Grammar-Kit BNF and JFlex, the parser produces a full AST for all DRL constructs. If one rule has a syntax error, the rest of the file still parses correctly.

• Package declarations, imports, globals
• Rule blocks with attributes (salience, no-loop, agenda-group, etc.)
• When-clause patterns with fact types, binding variables, and constraints
• Conditional elements (not, exists, forall, from, collect, accumulate, eval)
• Then-clause Java/MVEL action code
• Function definitions, type declarations, queries

Context-Aware Code Completion

Context	What's Suggested
File top level	package, import, global, rule, function, declare, query
Inside rule (before when)	salience, no-loop, agenda-group, ruleflow-group, timer, etc.
Inside when-clause	and, or, not, exists, forall, from, accumulate, eval
Inside then-clause	insert, update, modify, retract, delete, drools.halt
After $variable.	Methods and fields of the bound type
At type positions	Classes from project classpath with auto-import
Inside constraints	Bean properties of the fact type

Go-To-Definition (Ctrl+Click)

• Click on a class name in fact patterns, globals, or imports → navigate to Java source or decompiled class
• Click on a method/field after $variable. → navigate to the method or field definition on the bound type
• Click on a binding variable ($customer) → navigate to its declaration in the when-clause
• Supports chained access: $customer.address.city resolves each segment

Real-Time Validation

Check	Severity
Missing when/then/end clauses	Error
Incorrect clause order	Error
Unresolvable class in fact pattern	Error
Unresolvable import	Error
Unbalanced parentheses in constraints	Error
Invalid salience value (non-numeric)	Error
Invalid date format in attributes	Error
Unresolvable global type	Error
Unterminated string literals	Error
Duplicate rule names	Warning
Unused binding variables	Warning
Duplicate imports	Warning
Unused imports	Weak Warning

Quick Fixes

• Add missing import — one click to insert the import statement
• Remove unused import — clean up unused imports
• Rename duplicate rule — auto-append numeric suffix
• Add missing semicolon — insert ; at the right position
• Remove unused binding — convert $var : Type() to Type()

Structure View

Outline panel showing all rules, queries, functions, and declarations. Click to navigate.

Code Folding

Collapse rule blocks, import groups, declare blocks, queries, functions, and multi-line comments.

Bracket Matching & Commenter

• Automatic bracket matching for (), {}, []
• Toggle line comments (//) and block comments (/* */) with keyboard shortcuts

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Installation

From JetBrains Marketplace (Recommended)

1. Open IntelliJ IDEA
2. Go to File → Settings → Plugins
3. Search for "Drools Rule Checker"
4. Click Install and restart

Manual Installation

1. Download the latest .zip from GitHub Releases
2. Go to Settings → Plugins → ⚙️ → Install Plugin from Disk...
3. Select the ZIP file and restart

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Usage Example

package com.example.rules;

import com.example.model.Customer;
import com.example.model.Order;

global org.slf4j.Logger log;

rule "Apply Premium Discount"
    salience 100
    no-loop true
    when
        $customer : Customer(loyaltyTier == "PREMIUM", active == true)
        $order : Order(total > 500.00) from $customer.getOrders()
    then
        double discount = $order.getTotal() * 0.20;
        $order.setDiscount(discount);
        update($order);
        log.info("Applied 20% discount of {} to order {}", discount, $order.getId());
end

With this plugin installed, you get:

• Syntax highlighting for all elements
• Completion after $customer. showing Customer methods
• Completion after $order. showing Order methods
• Ctrl+Click on Customer navigates to the Java class
• Warning if $customer is declared but never used
• Error if Customer class can't be resolved on classpath

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Supported Drools Constructs

• ✅ Package declarations
• ✅ Import statements (including wildcard)
• ✅ Global declarations
• ✅ Rule definitions with all attributes
• ✅ When-clause patterns and constraints
• ✅ Binding variables ($var : Type())
• ✅ Conditional elements (not, exists, forall, from, collect, accumulate, eval)
• ✅ Then-clause Java/MVEL code
• ✅ Function definitions
• ✅ Type declarations (declare blocks)
• ✅ Query definitions

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Building from Source

Prerequisites

• Java 17+
• Gradle 8.0+ (wrapper included)
• IntelliJ IDEA 2024.2+ (for running/debugging)

Build Commands

git clone https://github.com/MohitPimoli/drool-rule-checker.git
cd drool-rule-checker

# Build the plugin
./gradlew clean buildPlugin

# Run in a sandboxed IDE for testing
./gradlew runIde

# Run tests
./gradlew test

Project Structure

src/main/
├── grammars/
│   ├── Drools.bnf          # Grammar-Kit BNF grammar
│   └── Drools.flex         # JFlex lexer specification
├── gen/                     # Generated parser and PSI classes
├── java/com/plugin/drool/
│   ├── DroolsLanguage.java
│   ├── DroolsParserDefinition.java
│   ├── DroolsLexerAdapter.java
│   ├── DroolsAnnotator.java           # PSI-based validation
│   ├── DroolsCompletionContributor.java # Context-aware completion
│   ├── DroolsReferenceContributor.java  # Go-to-definition
│   ├── DroolsStructureViewFactory.java  # Outline panel
│   ├── DroolsFoldingBuilder.java        # Code folding
│   ├── DroolsResolutionCache.java       # Class resolution cache
│   ├── util/
│   │   └── DotAccessExpressionResolver.java # $-binding expression reconstruction
│   ├── psi/mixin/                       # Typed PSI mixins
│   └── fixes/                           # Quick-fix actions
└── resources/META-INF/
    └── plugin.xml

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Compatibility

IDE	Version
IntelliJ IDEA Community	2025.0+
IntelliJ IDEA Ultimate	2025.0+

Requires the Java plugin to be enabled (for classpath resolution and go-to-definition).

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Contributing

Contributions welcome! See CONTRIBUTING.md for guidelines.

• 🐛 Report bugs
• 💡 Request features
• 🔧 Submit pull requests

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License

MIT License — see LICENSE for details.

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Links

• JetBrains Marketplace
• GitHub Repository
• Issue Tracker
• Changelog

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Keywords: Drools, DRL, IntelliJ IDEA plugin, Drools IDE, Drools editor, Drools syntax highlighting, Drools code completion, Drools validation, rule engine, business rules, JBoss Drools, KIE, .drl files, Drools IntelliJ, Drools JetBrains