feat: Add inlay hints in java

Author: CGNonofr

src/extensions/java.ts

@@ -2,9 +2,54 @@ import {
   DisposableCollection, MonacoLanguageClient
 } from 'monaco-languageclient'
 import { StaticFeature, FeatureState } from 'vscode-languageclient/lib/common/api'
-import { WorkspaceEdit } from 'vscode-languageserver-protocol'
+import { InlayHint, InlayHintParams, InlayHintRefreshRequest, InlayHintRequest, WorkspaceEdit } from 'vscode-languageserver-protocol'
 import * as vscode from 'vscode'
 
+async function asInlayHints (values: InlayHint[] | undefined | null, client: MonacoLanguageClient): Promise<vscode.InlayHint[] | undefined> {
+  if (!Array.isArray(values)) {
+    return undefined
+  }
+  return values.map(lsHint => asInlayHint(lsHint, client))
+}
+
+function asInlayHint (value: InlayHint, client: MonacoLanguageClient): vscode.InlayHint {
+  const label = value.label as string
+  const result = new vscode.InlayHint(client.protocol2CodeConverter.asPosition(value.position), label)
+  result.paddingRight = true
+  result.kind = vscode.InlayHintKind.Parameter
+  return result
+}
+
+/**
+ * Comes from https://github.com/redhat-developer/vscode-java/blob/9b6046eecc65fd47507f309a3ccc9add45c6d3be/src/inlayHintsProvider.ts#L5
+ */
+class JavaInlayHintsProvider implements vscode.InlayHintsProvider {
+  private onDidChange = new vscode.EventEmitter<void>()
+  public onDidChangeInlayHints = this.onDidChange.event
+
+  constructor (private client: MonacoLanguageClient) {
+    this.client.onRequest(InlayHintRefreshRequest.type, async () => {
+      this.onDidChange.fire()
+    })
+  }
+
+  public async provideInlayHints (document: vscode.TextDocument, range: vscode.Range, token: vscode.CancellationToken): Promise<vscode.InlayHint[] | undefined> {
+    const requestParams: InlayHintParams = {
+      textDocument: this.client.code2ProtocolConverter.asTextDocumentIdentifier(document),
+      range: this.client.code2ProtocolConverter.asRange(range)
+    }
+    try {
+      const values = await this.client.sendRequest(InlayHintRequest.type, requestParams, token)
+      if (token.isCancellationRequested) {
+        return []
+      }
+      return asInlayHints(values, this.client)
+    } catch (error) {
+      return this.client.handleFailedRequest(InlayHintRequest.type, token, error, [])
+    }
+  }
+}
+
 export class JavaExtensionFeature implements StaticFeature {
   private disposables: DisposableCollection
   constructor (private languageClient: MonacoLanguageClient) {
@@ -19,6 +64,8 @@ export class JavaExtensionFeature implements StaticFeature {
       const edit = await this.languageClient.protocol2CodeConverter.asWorkspaceEdit(obj)
       return vscode.workspace.applyEdit(edit)
     }))
+
+    this.disposables.push(vscode.languages.registerInlayHintsProvider(this.languageClient.clientOptions.documentSelector!, new JavaInlayHintsProvider(this.languageClient)))
   }
 
   getState (): FeatureState {