Feature Overview

The ReScript IntelliJ Plugin provides 90+ features organized into two layers:

Native features are built into the plugin and work without any external dependencies. They provide instant, offline functionality.

LSP features require the ReScript Language Server and provide semantic understanding of your code.

Features are grouped into eight categories: Syntax Highlighting, Code Completion, Navigation, Code Editing, Run & Build, Testing, Code Analysis, and Advanced Features. See the cards below for details on each category, or refer to the Native vs. LSP table for a summary of which features require the language server.

Feature Categories

Syntax Highlighting

JFlex lexer + LSP semantic tokens for accurate coloring.

Syntax Highlighting

Code Completion

Intelligent completions, postfix templates, and live templates.

Code Completion

Navigation

Go to Definition, Symbol, Related files, and more.

Navigation

Code Editing

Folding, formatting, intentions, surround, and smart editing.

Code Editing

Run & Build

Run configurations, gutter icons, and build status.

Run & Build

Testing

Jest/Vitest integration with test tree UI.

Testing

Code Analysis

Inspections, dead code analysis, and import optimization.

Code Analysis

Advanced Features

Code Lens, Compiled JS Preview, Module Hierarchy, .d.ts Binding Generation, Project Wizard, and more.

Advanced Features

Native vs. LSP Features

Feature	Native	LSP	Details
Syntax highlighting	Yes	Yes (semantic overlay)	Native lexer handles keyword, string, operator, and punctuation coloring. LSP adds semantic precision for variables, types, namespaces, and variant constructors.
Code folding	Yes		Collapses multi-line declarations, block comments, and region markers using the PSI tree. No semantic analysis needed.
Brace matching	Yes		Matches {}, [], (), and JSX tag brackets using token-level information from the lexer.
Comments toggle	Yes		Inserts or removes // and /* */ based on cursor position. Purely textual operation.
Structure view	Yes		Displays top-level declarations (let, type, module, external, open, include, exception) from the lightweight parser.
Live templates	Yes		Expands code snippets (e.g., let, switch, @react.component). Templates are defined within the plugin and need no external data.
Postfix templates	Yes		Transforms expressions via suffixes (.switch, .pipe, .log, .some, .ok, .error, .ignore). Works by rewriting text around the cursor.
File switching (Alt+O)	Yes		Toggles between .res and .resi by filename. No semantic understanding required.
Code completion		Yes	Provides context-aware completions for identifiers, record fields, module members, and variant constructors using the type system.
Go to Definition		Yes	Resolves the definition site of any symbol. Requires type analysis to follow module paths and aliases.
Hover documentation		Yes	Displays inferred types and doc comments on mouse hover. Relies on the compiler’s type information.
Find references		Yes	Locates all usages of a symbol across the project. Requires cross-file semantic analysis.
Diagnostics		Yes	Reports type errors, syntax errors, and warnings inline. Powered by the ReScript compiler via the language server.
Inlay hints		Yes	Shows inferred types next to let bindings and function parameters. Requires type inference from the compiler.
Rename		Yes	Renames a symbol and updates all references project-wide. Requires complete semantic understanding.
Code formatting		Yes (via CLI)	Invokes rescript format through the language server to format the current file.
Signature help		Yes	Displays parameter information when typing function arguments. Requires type analysis.
Code Lens		Yes	Shows type annotations above functions via the CodeVision API. Requires type inference.
Project Wizard	Yes		Creates new projects from 16 pre-configured templates. Generates all build files and starter code locally.

Understanding Native Features

Native features are powered entirely by the JFlex lexer and lightweight parser bundled within the plugin. They operate on the syntactic structure of ReScript code — tokenizing keywords, matching brackets, recognizing top-level declarations — without understanding types or semantics.

This means native features:

• Work instantly with zero startup delay, because there is no external process to launch.

• Function offline and in projects without node_modules, since they depend only on the plugin itself.

• Do not require @rescript/language-server or even Node.js to be installed.

Examples of purely syntactic operations include folding a module block (the parser sees the module keyword and matching braces), toggling a line comment (inserting // at the line start), and expanding a live template (replacing a text abbreviation with a predefined snippet).

Understanding LSP Features

LSP features communicate with @rescript/language-server over a stdio connection. The language server runs the ReScript compiler internally, giving it access to:

• Type inference — knowing that x is an int or that user.name is a string.

• Cross-file resolution — following open Belt to find Belt.Array.map.

• Error detection — reporting type mismatches, missing fields, and exhaustiveness warnings.

Because the language server performs full compilation, LSP features can provide rich, accurate information that would be impossible with syntax analysis alone. For example, Go to Definition can resolve a function imported through multiple module aliases, and code completion can suggest record fields that match the inferred type context.

Graceful Degradation When LSP Is Disconnected

The plugin is designed so that the absence of the language server never prevents basic editing. When the LSP connection is unavailable — for example, because @rescript/language-server is not installed, Node.js is missing, or the server process has crashed — the following behavior applies:

Features that continue to work normally:

• Syntax highlighting (lexer-based coloring for keywords, strings, numbers, operators, punctuation, module names, JSX tags, and decorators)

• Code folding for all recognized declarations

• Brace matching and auto-closing brackets

• Line and block comment toggling

• Structure view with top-level declaration outline

• Live templates and postfix templates

• File switching between .res and .resi

• Smart Enter and declaration up/down movement

• Surround With templates

Features that become unavailable:

• Code completion shows no suggestions (the completion popup does not appear for ReScript files).

• Go to Definition, Find Usages, and Hover do nothing when invoked.

• No diagnostic errors or warnings are displayed in the editor gutter or Problems panel.

• Inlay hints and Code Lens annotations are not shown.

• Rename refactoring is not available.

• Code formatting via Cmd+Option+L does not modify the file.

• Signature help does not appear when typing function arguments.

Visual indicator: When the language server cannot be found, the plugin displays an editor notification bar at the top of ReScript files with a message explaining that LSP features are unavailable and providing instructions for installing @rescript/language-server.

Recovery: Once the language server is installed or its path is configured in Settings > Languages & Frameworks > ReScript, the LSP connection is established automatically when a .res or .resi file is opened. All LSP features become available without restarting the IDE.