lsp: Use InitializeResult from lsp-types

Make the previous patch typesafe by enabling the "proposed" feature in
the `lsp-types` crate, so that the `InitializeResult` has the
`offsetEncoding` field.

Fix the fallout of this change.

tools/lsp/Cargo.toml

@@ -57,7 +57,7 @@ i-slint-compiler = { version = "=0.2.6", path = "../../internal/compiler"}
 clap = { version = "3.2", features = ["derive", "wrap_help"] }
 dunce = "1.0.1"
 euclid = "0.22"
-lsp-types = "0.93.0"
+lsp-types = { version = "0.93.0", features = ["proposed"] }
 serde = "1.0.118"
 serde_json = "1.0.60"
 

tools/lsp/main.rs

@@ -14,7 +14,10 @@ mod util;
 
 use i_slint_compiler::CompilerConfiguration;
 use lsp_types::notification::{DidChangeTextDocument, DidOpenTextDocument, Notification};
-use lsp_types::{DidChangeTextDocumentParams, DidOpenTextDocumentParams, InitializeParams};
+use lsp_types::{
+    DidChangeTextDocumentParams, DidOpenTextDocumentParams, InitializeParams, InitializeResult,
+    ServerInfo,
+};
 use server_loop::*;
 
 use clap::Parser;
@@ -128,18 +131,18 @@ fn main() {
 pub fn run_lsp_server() -> Result<(), Error> {
     let (connection, io_threads) = Connection::stdio();
     let (id, params) = connection.initialize_start()?;
-    let server_capabilities = server_loop::server_capabilities();
 
-    let initialize_data = serde_json::json!({
-        "capabilities": server_capabilities,
-        "offsetEncoding": "utf-8", // We support utf-8 *only*
-        "serverInfo": {
-            "name": "slint-ls",
-            "version": String::from(env!("CARGO_PKG_VERSION")),
-        }
-    });
+    let initialization_reply = InitializeResult {
+        capabilities: server_loop::server_capabilities(),
 
-    connection.initialize_finish(id, initialize_data)?;
+        server_info: Some(ServerInfo {
+            name: "slint-ls".into(),
+            version: Some(env!("CARGO_PKG_VERSION").to_string()),
+        }),
+        offset_encoding: Some("utf-8".to_string()),
+    };
+
+    connection.initialize_finish(id, serde_json::to_value(initialization_reply)?)?;
 
     main_loop(&connection, params)?;
     io_threads.join()?;

tools/lsp/server_loop.rs

@@ -114,6 +114,7 @@ pub fn server_capabilities() -> ServerCapabilities {
             trigger_characters: Some(vec![".".to_owned()]),
             work_done_progress_options: WorkDoneProgressOptions::default(),
             all_commit_characters: None,
+            completion_item: None,
         }),
         definition_provider: Some(OneOf::Left(true)),
         text_document_sync: Some(TextDocumentSyncCapability::Kind(