#### Signature Help Request (:leftwards_arrow_with_hook:)
The signature help request is sent from the client to the server to request signature information at a given cursor position.
_Client Capability_:
* property name (optional): `textDocument.signatureHelp`
* property type: `SignatureHelpClientCapabilities` defined as follows:
```typescript
export interface SignatureHelpClientCapabilities {
/**
* Whether signature help supports dynamic registration.
*/
dynamicRegistration?: boolean;
/**
* The client supports the following `SignatureInformation`
* specific properties.
*/
signatureInformation?: {
/**
* Client supports the follow content formats for the documentation
* property. The order describes the preferred format of the client.
*/
documentationFormat?: MarkupKind[];
/**
* Client capabilities specific to parameter information.
*/
parameterInformation?: {
/**
* The client supports processing label offsets instead of a
* simple label string.
*
* @since 3.14.0
*/
labelOffsetSupport?: boolean;
};
/**
* The client supports the `activeParameter` property on
* `SignatureInformation` literal.
*
* @since 3.16.0
*/
activeParameterSupport?: boolean;
};
/**
* The client supports to send additional context information for a
* `textDocument/signatureHelp` request. A client that opts into
* contextSupport will also support the `retriggerCharacters` on
* `SignatureHelpOptions`.
*
* @since 3.15.0
*/
contextSupport?: boolean;
}
```
_Server Capability_:
* property name (optional): `signatureHelpProvider`
* property type: `SignatureHelpOptions` defined as follows:
```typescript
export interface SignatureHelpOptions extends WorkDoneProgressOptions {
/**
* The characters that trigger signature help
* automatically.
*/
triggerCharacters?: string[];
/**
* List of characters that re-trigger signature help.
*
* These trigger characters are only active when signature help is already
* showing. All trigger characters are also counted as re-trigger
* characters.
*
* @since 3.15.0
*/
retriggerCharacters?: string[];
}
```
_Registration Options_: `SignatureHelpRegistrationOptions` defined as follows:
```typescript
export interface SignatureHelpRegistrationOptions
extends TextDocumentRegistrationOptions, SignatureHelpOptions {
}
```
_Request_:
* method: `textDocument/signatureHelp`
* params: `SignatureHelpParams` defined as follows:
```typescript
export interface SignatureHelpParams extends TextDocumentPositionParams,
WorkDoneProgressParams {
/**
* The signature help context. This is only available if the client
* specifies to send this using the client capability
* `textDocument.signatureHelp.contextSupport === true`
*
* @since 3.15.0
*/
context?: SignatureHelpContext;
}
```
```typescript
/**
* How a signature help was triggered.
*
* @since 3.15.0
*/
export namespace SignatureHelpTriggerKind {
/**
* Signature help was invoked manually by the user or by a command.
*/
export const Invoked: 1 = 1;
/**
* Signature help was triggered by a trigger character.
*/
export const TriggerCharacter: 2 = 2;
/**
* Signature help was triggered by the cursor moving or by the document
* content changing.
*/
export const ContentChange: 3 = 3;
}
export type SignatureHelpTriggerKind = 1 | 2 | 3;
```
```typescript
/**
* Additional information about the context in which a signature help request
* was triggered.
*
* @since 3.15.0
*/
export interface SignatureHelpContext {
/**
* Action that caused signature help to be triggered.
*/
triggerKind: SignatureHelpTriggerKind;
/**
* Character that caused signature help to be triggered.
*
* This is undefined when triggerKind !==
* SignatureHelpTriggerKind.TriggerCharacter
*/
triggerCharacter?: string;
/**
* `true` if signature help was already showing when it was triggered.
*
* Retriggers occur when the signature help is already active and can be
* caused by actions such as typing a trigger character, a cursor move, or
* document content changes.
*/
isRetrigger: boolean;
/**
* The currently active `SignatureHelp`.
*
* The `activeSignatureHelp` has its `SignatureHelp.activeSignature` field
* updated based on the user navigating through available signatures.
*/
activeSignatureHelp?: SignatureHelp;
}
```
_Response_:
* result: `SignatureHelp` \| `null` defined as follows:
```typescript
/**
* Signature help represents the signature of something
* callable. There can be multiple signature but only one
* active and only one active parameter.
*/
export interface SignatureHelp {
/**
* One or more signatures. If no signatures are available the signature help
* request should return `null`.
*/
signatures: SignatureInformation[];
/**
* The active signature. If omitted or the value lies outside the
* range of `signatures` the value defaults to zero or is ignore if
* the `SignatureHelp` as no signatures.
*
* Whenever possible implementors should make an active decision about
* the active signature and shouldn't rely on a default value.
*
* In future version of the protocol this property might become
* mandatory to better express this.
*/
activeSignature?: uinteger;
/**
* The active parameter of the active signature. If omitted or the value
* lies outside the range of `signatures[activeSignature].parameters`
* defaults to 0 if the active signature has parameters. If
* the active signature has no parameters it is ignored.
*
* Since version 3.16.0 the `SignatureInformation` itself provides a
* `activeParameter` property and it should be used instead of this one.
*/
activeParameter?: uinteger;
}
```
```typescript
/**
* Represents the signature of something callable. A signature
* can have a label, like a function-name, a doc-comment, and
* a set of parameters.
*/
export interface SignatureInformation {
/**
* The label of this signature. Will be shown in
* the UI.
*/
label: string;
/**
* The human-readable doc-comment of this signature. Will be shown
* in the UI but can be omitted.
*/
documentation?: string | MarkupContent;
/**
* The parameters of this signature.
*/
parameters?: ParameterInformation[];
/**
* The index of the active parameter.
*
* If provided, this is used in place of `SignatureHelp.activeParameter`.
*
* @since 3.16.0
*/
activeParameter?: uinteger;
}
```
```typescript
/**
* Represents a parameter of a callable-signature. A parameter can
* have a label and a doc-comment.
*/
export interface ParameterInformation {
/**
* The label of this parameter information.
*
* Either a string or an inclusive start and exclusive end offsets within
* its containing signature label. (see SignatureInformation.label). The
* offsets are based on a UTF-16 string representation as `Position` and
* `Range` does.
*
* *Note*: a label of type string should be a substring of its containing
* signature label. Its intended use case is to highlight the parameter
* label part in the `SignatureInformation.label`.
*/
label: string | [uinteger, uinteger];
/**
* The human-readable doc-comment of this parameter. Will be shown
* in the UI but can be omitted.
*/
documentation?: string | MarkupContent;
}
```
* error: code and message set in case an exception happens during the signature help request.