JDT LS should mention as capability that it can support willRenameFiles

[angelozerr]

I have tested quicly JDT LS inside IntelliJ with https://github.com/redhat-developer/lsp4ij with my current willRenameFiles LSP client support and it doesn't work because JDT LS doesn't return the proper server capability.

It is working on vscode-java because you did some hack https://github.com/redhat-developer/vscode-java/blob/9bfd8a89b7f2259757999443adda0d5a7a505cc8/src/fileEventHandler.ts#L141

I think JDT LS should return this kind of capability:

[Trace - 4:38:09 PM] Received response 'initialize - (0)' in 7241ms.
Result: {
    "capabilities": {
  ...
        },
        "workspace": {
            "fileOperations": {
                "willRename": {
                    "filters": [
                        {
                            "scheme": "file",
                            "pattern": {
                                "glob": "**/*.{java}",
                                "matches": "file"
                            }
                        }
                    ]
                },
                "didRename": {
                    "filters": [
                        {
                            "scheme": "file",
                            "pattern": {
                                "glob": "**/*.{java}",
                                "matches": "file"
                            }
                        }
                    ]
                }
            }
        }
...
}

And if there are some good reason why you did this hack and if server capability returns that, it could break vscode-java, perhaps JDT LS could receive a property to say "please return me the workspace.fileOperations' capability.

[rgrunber]

My guess would be we never properly set :

/**
   * The server is interested in receiving willRenameFiles requests.
    */
willRename?: FileOperationRegistrationOptions;

eclipse.jdt.ls/org.eclipse.jdt.ls.core/src/org/eclipse/jdt/ls/core/internal/handlers/InitHandler.java

Lines 218 to 223 in d518f6d

	WorkspaceServerCapabilities wsCapabilities = new WorkspaceServerCapabilities();
	WorkspaceFoldersOptions wsFoldersOptions = new WorkspaceFoldersOptions();
	wsFoldersOptions.setSupported(Boolean.TRUE);
	wsFoldersOptions.setChangeNotifications(Boolean.TRUE);
	wsCapabilities.setWorkspaceFolders(wsFoldersOptions);
	capabilities.setWorkspace(wsCapabilities);

So maybe clients are respecting that and we need to declare it.