No completion results while inserting trait method names while inside a proc_macro

Completion inside a macro appears to not work. I was working on a language server using tower-lsp, which looks like this:

#[tower_lsp::async_trait]
impl LanguageServer for Backend {
    async fn did_change_configuration(&self, _: DidChangeConfigurationParams) {}
    async fn did_open(&self, _: DidOpenTextDocumentParams) {}

    async fn initialize(&self, _: InitializeParams) -> Result<InitializeResult> {
        Ok(InitializeResult {
            capabilities: ServerCapabilities {
                hover_provider: Some(HoverProviderCapability::Simple(true)),
                completion_provider: Some(CompletionOptions::default()),
                ..Default::default()
            },
            ..Default::default()
        })
    }

    async fn initialized(&self, _: InitializedParams) {
        self.client
            .log_message(MessageType::INFO, "server initialized!")
            .await;
    }

    async fn shutdown(&self) -> Result<()> {
        Ok(())
    }

    async fn completion(&self, _: CompletionParams) -> Result<Option<CompletionResponse>> {
        Ok(Some(CompletionResponse::Array(vec![
            CompletionItem::new_simple("Hello".to_string(), "Some detail".to_string()),
            CompletionItem::new_simple("Bye".to_string(), "More detail".to_string()),
        ])))
    }

    async fn hover(&self, _: HoverParams) -> Result<Option<Hover>> {
        Ok(Some(Hover {
            contents: HoverContents::Scalar(MarkedString::String("You're hovering!".to_string())),
            range: None,
        }))
    }
}

Autocompletion for the new methods at the top, did_change_configuration and did_open, did not return any results. Expected behavior would be the traits of the method.

Reproduce the issue with the supplied tower-lsp LanguageServer example, focusing on completion for the trait methods inside the proc_macro. Compare completion behavior for the existing methods with the expected trait methods, and consider the issue done when those methods produce completion results.