Inlay Hints

Inlay Parameter Hints Provider

Inlay parameter hints are simple string inline inlays placed before parameter names in method and function calls. It is not possible to provide advanced presentation and behavior of inlay parameter hints.

To provide inlay parameter hints, implement InlayParameterHintsProvider and register it in com.intellij.codeInsight.parameterNameHints extension point (EP). The API documentation of InlayParameterHintsProvider explains in detail the rationale behind all methods.

Examples:

• GroovyInlayParameterHintsProvider - shows parameter hints in Groovy code

• KotlinInlayParameterHintsProvider - shows parameter hints in Kotlin code

To suppress inlay parameter hints in specific places, implement ParameterNameHintsSuppressor and register it in com.intellij.codeInsight.parameterNameHintsSuppressor EP.

Declarative Inlay Hints Provider

Declarative inlay hints are inline textual inlays that can hold expandable list of clickable items. Please note this API has limited presentation customization possibilities due to its UI-independent design, which allows utilizing it by different frontend technologies (not only in Swing).

To provide declarative inlay hints implement declarative InlayHintsProvider and register it in com.intellij.codeInsight.declarativeInlayProvider EP. See the API documentation for the details.

Examples:

• JavaImplicitTypeDeclarativeInlayHintsProvider - shows inferred type for variables declared with the var keyword in Java code when the inferred type may not be clear

• JavaMethodChainsDeclarativeInlayProvider - shows method return types in call chains in Java code

To provide a custom configuration UI, implement InlayHintsCustomSettingsProvider registered in com.intellij.codeInsight.declarativeInlayProviderCustomSettingsProvider extension point.

Code Vision Provider

Code vision provider allows for providing block inlay hints for elements like class, method, field, etc. If there are multiple hints provided for a single element, all will be displayed in the same line to save vertical space.

Code vision hints can be displayed over the element, or on the right, at the end of line. It is configurable by users in Settings | Editor | Inlay Hints | Code vision by choosing a value in Default position for metrics combo box, or by selecting Position in specific provider entries.

There are three extension points for implementing a code vision provider:

• DaemonBoundCodeVisionProvider registered in com.intellij.codeInsight.daemonBoundCodeVisionProvider EP

• CodeVisionProvider registered in com.intellij.codeInsight.codeVisionProvider EP

• CodeVisionGroupSettingProvider registered in com.intellij.config.codeVisionGroupSettingProvider EP

DaemonBoundCodeVisionProvider API should be used in cases when code vision entries are related to PSI, so that calculated values are invalidated and recalculated on PSI changes.

CodeVisionProvider API should be used for cases when presented information doesn't depend on the PSI.

The CodeVisionGroupSettingProvider is necessary for displaying the name and description of the code vision provider in the settings. The groupId must match the value specified in the implementation of the CodeVisionProvider; if not specified, it defaults to the id. The groupName is the name shown in the code vision group, and the description will be visible in the right details panel.

Examples:

• JavaInheritorsCodeVisionProvider - shows number of Java class or method inheritors. Clicking the inlay hint opens the list of inheritors. This provider is DaemonBoundCodeVisionProvider.

• JavaReferencesCodeVisionProvider - shows number of usages of Java class or member. Clicking the inlay opens the list of usages or navigates to the usage if only one exists. This provider is DaemonBoundCodeVisionProvider.

• VcsCodeVisionProvider - shows the author of a given element, e.g., class or method, based on VCS information. This provider is CodeVisionProvider.

Inlay Hints Provider

Inlay hints provider allows for implementing both inline and block inlay hints with custom presentation and behavior. See the API documentation for the details.

To provide inlay hints, implement InlayHintsProvider and register it in com.intellij.codeInsight.inlayProvider EP. See the API documentation for the details.

Examples:

• GroovyLocalVariableTypeHintsInlayProvider - shows local variable types in Groovy code

• MarkdownTableInlayProvider - decorates tables in Markdown files.

• For a more complex example, see KotlinLambdasHintsProvider, its parent class and all implementations.

Further Tips

1. Go to Settings | Editor | Inlay Hints (Product Help) and check out inlays that have already been implemented.

2. To support multiple languages with a single type of inlay hints, see declarative InlayHintsProviderFactory (2023.1+) or InlayHintsProviderFactory (pre-2023.1).

3. For testing inlay hints, see InlayHintsProviderTestCase and InlayParameterHintsTest.