Bracketbow

A free, open-source alternative to the Rainbow Brackets plugin for IntelliJ-based IDEs. Colors ( ), [ ], { } brackets by nesting depth.

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Requirements

• JDK 17+ (JDK 21 recommended)
• IntelliJ IDEA Community (free) or Ultimate
• Internet connection for the first Gradle run (~500 MB download)

Quick Start

# Open the project in IntelliJ (File → Open → this folder)
# Wait for Gradle sync, then:

./gradlew runIde      # Launches a sandbox IDE with the plugin loaded
./gradlew buildPlugin # Produces a distributable .zip

Install the built build/distributions/bracketbow-0.1.0.zip in your real IDE via: Settings → Plugins → ⚙ → Install Plugin from Disk...

On Windows use gradlew.bat runIde

Settings

Settings → Tools → Bracketbow

• Enable/disable the plugin globally
• Color level count — how many levels before colors cycle (3–10)
• Bracket types — toggle round ( ), square [ ], and curly { } independently
• Languages — enable/disable per language (Java, Kotlin, XML, HTML, JSON)
• Edit colors — opens Settings → Editor → Color Scheme → Bracketbow

Architecture

Code is split into packages by responsibility:

src/main/kotlin/com/bracketbow/
├── psi/
│   ├── BracketDetector.kt    ← Is this element a bracket? (pure logic)
│   └── DepthCalculator.kt    ← How deep is this bracket nested? (pure logic)
├── colors/
│   ├── BracketbowColors.kt              ← Color level definitions
│   └── BracketbowColorSettingsPage.kt   ← Color Scheme settings page
├── settings/
│   ├── BracketbowSettings.kt            ← PersistentStateComponent
│   └── BracketbowConfigurable.kt        ← Settings UI (Kotlin UI DSL v2)
└── annotator/
    └── BracketbowAnnotator.kt           ← Thin coordinator

Each file does exactly one thing. Classes in psi/ have no IntelliJ API dependency beyond PsiElement and are easily unit-testable. The annotator just wires the pieces together.

Data flow

IntelliJ              BracketbowAnnotator     psi/                  colors/
  │                          │                   │                      │
  │── annotate(element) ────►│                   │                      │
  │                          │── isBracketLeaf() ►│                      │
  │                          │◄── true/false ─────│                      │
  │                          │── depthOf(element) ►│                      │
  │                          │◄── int ─────────────│                      │
  │                          │── forDepth(depth) ───────────────────────►│
  │                          │◄── TextAttributesKey ────────────────────│
  │◄── annotation ───────────│                   │                      │

How depth is calculated

For the innermost ( in ((())):

1. BracketDetector.isBracketLeaf → true
2. DepthCalculator.depthOf:
   • parent #1: innermost paren expression → isBracketGroup true → depth 0
   • parent #2: middle paren expression → true → depth 1
   • parent #3: outermost paren expression → true → depth 2
   • parent #4: file/statement → false → stop
3. BracketbowColors.forDepth(2) → BRACKETBOW_LEVEL_2
4. IntelliJ applies the corresponding color

Development

./gradlew runIde       # Live test in sandbox IDE
./gradlew buildPlugin  # Build distributable zip
./gradlew verifyPlugin # JetBrains compatibility check
./gradlew clean        # Fix stuck Gradle builds

Requires JDK 17. If your active JDK is newer and Gradle fails, prefix with: JAVA_HOME=/path/to/jdk17 ./gradlew ...

License

MIT — see LICENSE.