diff --git a/README.md b/README.md
index 4de9887..3b9f774 100644
--- a/README.md
+++ b/README.md
@@ -79,6 +79,7 @@ The following options are currently available.
 | `include_at_in_builtins` | `bool` | `false` | Whether the @ sign should be part of the completion of builtins |
 | `skip_std_references` | `bool` | `false` | When true, skips searching for references in std. Improves lookup speed for functions in user's code. Renaming and go-to-definition will continue to work as is |
 | `max_detail_length` | `usize` | `1048576` | The detail field of completions is truncated to be no longer than this (in bytes) |
+| `prefer_ast_check_as_child_process` | `bool` | `true` | Can be used in conjuction with `enable_ast_check_diagnostics` to favor using `zig ast-check` instead of ZLS's fork |
 | `record_session` | `bool` | `false` | When true, zls will record all request is receives and write in into `record_session_path`, so that they can replayed with `zls replay` |
 | `record_session_path` | `?[]const u8` | `null` | Output file path when `record_session` is set. The recommended file extension *.zlsreplay |
 | `replay_session_path` | `?[]const u8` | `null` | Used when calling `zls replay` for specifying the replay file. If no extra argument is given `record_session_path` is used as the default path. |
diff --git a/schema.json b/schema.json
index 894e8ba..59931d2 100644
--- a/schema.json
+++ b/schema.json
@@ -94,6 +94,11 @@
             "type": "integer",
             "default": "1048576"
         },
+        "prefer_ast_check_as_child_process": {
+            "description": "Can be used in conjuction with `enable_ast_check_diagnostics` to favor using `zig ast-check` instead of ZLS's fork",
+            "type": "boolean",
+            "default": "true"
+        },
         "record_session": {
             "description": "When true, zls will record all request is receives and write in into `record_session_path`, so that they can replayed with `zls replay`",
             "type": "boolean",
diff --git a/src/Config.zig b/src/Config.zig
index c198a24..d9fd7cf 100644
--- a/src/Config.zig
+++ b/src/Config.zig
@@ -61,6 +61,9 @@ skip_std_references: bool = false,
 /// The detail field of completions is truncated to be no longer than this (in bytes)
 max_detail_length: usize = 1048576,
 
+/// Can be used in conjuction with `enable_ast_check_diagnostics` to favor using `zig ast-check` instead of ZLS's fork
+prefer_ast_check_as_child_process: bool = true,
+
 /// When true, zls will record all request is receives and write in into `record_session_path`, so that they can replayed with `zls replay`
 record_session: bool = false,
 
diff --git a/src/DocumentStore.zig b/src/DocumentStore.zig
index ee90de1..1da039e 100644
--- a/src/DocumentStore.zig
+++ b/src/DocumentStore.zig
@@ -13,6 +13,8 @@ const Config = @import("Config.zig");
 const ZigVersionWrapper = @import("ZigVersionWrapper.zig");
 const translate_c = @import("translate_c.zig");
 const ComptimeInterpreter = @import("ComptimeInterpreter.zig");
+const AstGen = @import("stage2/AstGen.zig");
+const Zir = @import("stage2/Zir.zig");
 
 const DocumentStore = @This();
 
@@ -56,6 +58,13 @@ pub const Handle = struct {
     uri: Uri,
     text: [:0]const u8,
     tree: Ast,
+    /// do not access unless `zir_status != .none`
+    zir: Zir = undefined,
+    zir_status: enum {
+        none,
+        outdated,
+        done,
+    } = .none,
     /// Not null if a ComptimeInterpreter is actually used
     interpreter: ?*ComptimeInterpreter = null,
     document_scope: analysis.DocumentScope,
@@ -74,6 +83,7 @@ pub const Handle = struct {
             allocator.destroy(interpreter);
         }
         self.document_scope.deinit(allocator);
+        if (self.zir_status != .none) self.zir.deinit(allocator);
         self.tree.deinit(allocator);
         allocator.free(self.text);
         allocator.free(self.uri);
@@ -214,6 +224,15 @@ pub fn refreshDocument(self: *DocumentStore, uri: Uri, new_text: [:0]const u8) !
     handle.tree.deinit(self.allocator);
     handle.tree = new_tree;
 
+    if (self.wantZir() and handle.open and new_tree.errors.len == 0) {
+        const new_zir = try AstGen.generate(self.allocator, new_tree);
+        if (handle.zir_status != .none) handle.zir.deinit(self.allocator);
+        handle.zir = new_zir;
+        handle.zir_status = .done;
+    } else if (handle.zir_status == .done) {
+        handle.zir_status = .outdated;
+    }
+
     var new_document_scope = try analysis.makeDocumentScope(self.allocator, handle.tree);
     handle.document_scope.deinit(self.allocator);
     handle.document_scope = new_document_scope;
@@ -696,17 +715,31 @@ fn createDocument(self: *DocumentStore, uri: Uri, text: [:0]const u8, open: bool
         var tree = try Ast.parse(self.allocator, text, .zig);
         errdefer tree.deinit(self.allocator);
 
+        // remove unused capacity
         var nodes = tree.nodes.toMultiArrayList();
         try nodes.setCapacity(self.allocator, nodes.len);
         tree.nodes = nodes.slice();
 
+        // remove unused capacity
         var tokens = tree.tokens.toMultiArrayList();
         try tokens.setCapacity(self.allocator, tokens.len);
         tree.tokens = tokens.slice();
 
+        const generate_zir = self.wantZir() and open and tree.errors.len == 0;
+        var zir: ?Zir = if (generate_zir) try AstGen.generate(self.allocator, tree) else null;
+        errdefer if (zir) |*code| code.deinit(self.allocator);
+
+        // remove unused capacity
+        if (zir) |*code| {
+            var instructions = code.instructions.toMultiArrayList();
+            try instructions.setCapacity(self.allocator, instructions.len);
+            code.instructions = instructions.slice();
+        }
+
         var document_scope = try analysis.makeDocumentScope(self.allocator, tree);
         errdefer document_scope.deinit(self.allocator);
 
+        // remove unused capacity
         try document_scope.scopes.setCapacity(self.allocator, document_scope.scopes.len);
 
         break :blk Handle{
@@ -714,6 +747,8 @@ fn createDocument(self: *DocumentStore, uri: Uri, text: [:0]const u8, open: bool
             .uri = duped_uri,
             .text = text,
             .tree = tree,
+            .zir = if (zir) |code| code else undefined,
+            .zir_status = if (zir != null) .done else .none,
             .document_scope = document_scope,
         };
     };
@@ -1082,6 +1117,12 @@ pub fn enumCompletionItems(self: DocumentStore, arena: std.mem.Allocator, handle
     return try self.tagStoreCompletionItems(arena, handle, "enum_completions");
 }
 
+pub fn wantZir(self: DocumentStore) bool {
+    if (!self.config.enable_ast_check_diagnostics) return false;
+    const can_run_ast_check = std.process.can_spawn and self.config.zig_exe_path != null and self.config.prefer_ast_check_as_child_process;
+    return !can_run_ast_check;
+}
+
 pub fn ensureInterpreterExists(self: *DocumentStore, uri: Uri) !*ComptimeInterpreter {
     var handle = self.handles.get(uri).?;
     if (handle.interpreter != null) return handle.interpreter.?;
diff --git a/src/Server.zig b/src/Server.zig
index 17fb4b2..e2f31dd 100644
--- a/src/Server.zig
+++ b/src/Server.zig
@@ -29,6 +29,7 @@ const completions = @import("features/completions.zig");
 const goto = @import("features/goto.zig");
 const hover_handler = @import("features/hover.zig");
 const selection_range = @import("features/selection_range.zig");
+const diagnostics_gen = @import("features/diagnostics.zig");
 
 const tres = @import("tres");
 
@@ -209,285 +210,6 @@ fn showMessage(
     });
 }
 
-fn generateDiagnostics(server: *Server, handle: DocumentStore.Handle) error{OutOfMemory}!types.PublishDiagnosticsParams {
-    const tracy_zone = tracy.trace(@src());
-    defer tracy_zone.end();
-
-    std.debug.assert(server.client_capabilities.supports_publish_diagnostics);
-
-    const tree = handle.tree;
-
-    var allocator = server.arena.allocator();
-    var diagnostics = std.ArrayListUnmanaged(types.Diagnostic){};
-
-    for (tree.errors) |err| {
-        var mem_buffer: [256]u8 = undefined;
-        var fbs = std.io.fixedBufferStream(&mem_buffer);
-        tree.renderError(err, fbs.writer()) catch if (std.debug.runtime_safety) unreachable else continue; // if an error occurs here increase buffer size
-
-        try diagnostics.append(allocator, .{
-            .range = offsets.tokenToRange(tree, err.token, server.offset_encoding),
-            .severity = .Error,
-            .code = .{ .string = @tagName(err.tag) },
-            .source = "zls",
-            .message = try server.arena.allocator().dupe(u8, fbs.getWritten()),
-            // .relatedInformation = undefined
-        });
-    }
-
-    if (server.config.enable_ast_check_diagnostics and tree.errors.len == 0) {
-        getAstCheckDiagnostics(server, handle, &diagnostics) catch |err| {
-            log.err("failed to run ast-check: {}", .{err});
-        };
-    }
-
-    if (server.config.warn_style) {
-        var node: u32 = 0;
-        while (node < tree.nodes.len) : (node += 1) {
-            if (ast.isBuiltinCall(tree, node)) {
-                const builtin_token = tree.nodes.items(.main_token)[node];
-                const call_name = tree.tokenSlice(builtin_token);
-
-                if (!std.mem.eql(u8, call_name, "@import")) continue;
-
-                var buffer: [2]Ast.Node.Index = undefined;
-                const params = ast.builtinCallParams(tree, node, &buffer).?;
-
-                if (params.len != 1) continue;
-
-                const import_str_token = tree.nodes.items(.main_token)[params[0]];
-                const import_str = tree.tokenSlice(import_str_token);
-
-                if (std.mem.startsWith(u8, import_str, "\"./")) {
-                    try diagnostics.append(allocator, .{
-                        .range = offsets.tokenToRange(tree, import_str_token, server.offset_encoding),
-                        .severity = .Hint,
-                        .code = .{ .string = "dot_slash_import" },
-                        .source = "zls",
-                        .message = "A ./ is not needed in imports",
-                    });
-                }
-            }
-        }
-
-        // TODO: style warnings for types, values and declarations below root scope
-        if (tree.errors.len == 0) {
-            for (tree.rootDecls()) |decl_idx| {
-                const decl = tree.nodes.items(.tag)[decl_idx];
-                switch (decl) {
-                    .fn_proto,
-                    .fn_proto_multi,
-                    .fn_proto_one,
-                    .fn_proto_simple,
-                    .fn_decl,
-                    => blk: {
-                        var buf: [1]Ast.Node.Index = undefined;
-                        const func = tree.fullFnProto(&buf, decl_idx).?;
-                        if (func.extern_export_inline_token != null) break :blk;
-
-                        if (func.name_token) |name_token| {
-                            const is_type_function = Analyser.isTypeFunction(tree, func);
-
-                            const func_name = tree.tokenSlice(name_token);
-                            if (!is_type_function and !Analyser.isCamelCase(func_name)) {
-                                try diagnostics.append(allocator, .{
-                                    .range = offsets.tokenToRange(tree, name_token, server.offset_encoding),
-                                    .severity = .Hint,
-                                    .code = .{ .string = "bad_style" },
-                                    .source = "zls",
-                                    .message = "Functions should be camelCase",
-                                });
-                            } else if (is_type_function and !Analyser.isPascalCase(func_name)) {
-                                try diagnostics.append(allocator, .{
-                                    .range = offsets.tokenToRange(tree, name_token, server.offset_encoding),
-                                    .severity = .Hint,
-                                    .code = .{ .string = "bad_style" },
-                                    .source = "zls",
-                                    .message = "Type functions should be PascalCase",
-                                });
-                            }
-                        }
-                    },
-                    else => {},
-                }
-            }
-        }
-    }
-
-    for (handle.cimports.items(.hash), handle.cimports.items(.node)) |hash, node| {
-        const result = server.document_store.cimports.get(hash) orelse continue;
-        if (result != .failure) continue;
-        const stderr = std.mem.trim(u8, result.failure, " ");
-
-        var pos_and_diag_iterator = std.mem.split(u8, stderr, ":");
-        _ = pos_and_diag_iterator.next(); // skip file path
-        _ = pos_and_diag_iterator.next(); // skip line
-        _ = pos_and_diag_iterator.next(); // skip character
-
-        try diagnostics.append(allocator, .{
-            .range = offsets.nodeToRange(handle.tree, node, server.offset_encoding),
-            .severity = .Error,
-            .code = .{ .string = "cImport" },
-            .source = "zls",
-            .message = try allocator.dupe(u8, pos_and_diag_iterator.rest()),
-        });
-    }
-
-    if (server.config.highlight_global_var_declarations) {
-        const main_tokens = tree.nodes.items(.main_token);
-        const tags = tree.tokens.items(.tag);
-        for (tree.rootDecls()) |decl| {
-            const decl_tag = tree.nodes.items(.tag)[decl];
-            const decl_main_token = tree.nodes.items(.main_token)[decl];
-
-            switch (decl_tag) {
-                .simple_var_decl,
-                .aligned_var_decl,
-                .local_var_decl,
-                .global_var_decl,
-                => {
-                    if (tags[main_tokens[decl]] != .keyword_var) continue; // skip anything immutable
-                    // uncomment this to get a list :)
-                    //log.debug("possible global variable \"{s}\"", .{tree.tokenSlice(decl_main_token + 1)});
-                    try diagnostics.append(allocator, .{
-                        .range = offsets.tokenToRange(tree, decl_main_token, server.offset_encoding),
-                        .severity = .Hint,
-                        .code = .{ .string = "highlight_global_var_declarations" },
-                        .source = "zls",
-                        .message = "Global var declaration",
-                    });
-                },
-                else => {},
-            }
-        }
-    }
-
-    if (handle.interpreter) |int| {
-        try diagnostics.ensureUnusedCapacity(allocator, int.errors.count());
-
-        var err_it = int.errors.iterator();
-
-        while (err_it.next()) |err| {
-            diagnostics.appendAssumeCapacity(.{
-                .range = offsets.nodeToRange(tree, err.key_ptr.*, server.offset_encoding),
-                .severity = .Error,
-                .code = .{ .string = err.value_ptr.code },
-                .source = "zls",
-                .message = err.value_ptr.message,
-            });
-        }
-    }
-    // try diagnostics.appendSlice(allocator, handle.interpreter.?.diagnostics.items);
-
-    return .{
-        .uri = handle.uri,
-        .diagnostics = diagnostics.items,
-    };
-}
-
-fn getAstCheckDiagnostics(
-    server: *Server,
-    handle: DocumentStore.Handle,
-    diagnostics: *std.ArrayListUnmanaged(types.Diagnostic),
-) !void {
-    var allocator = server.arena.allocator();
-
-    const zig_exe_path = server.config.zig_exe_path orelse return;
-
-    var process = std.ChildProcess.init(&[_][]const u8{ zig_exe_path, "ast-check", "--color", "off" }, server.allocator);
-    process.stdin_behavior = .Pipe;
-    process.stderr_behavior = .Pipe;
-
-    process.spawn() catch |err| {
-        log.warn("Failed to spawn zig ast-check process, error: {}", .{err});
-        return;
-    };
-    try process.stdin.?.writeAll(handle.text);
-    process.stdin.?.close();
-
-    process.stdin = null;
-
-    const stderr_bytes = try process.stderr.?.reader().readAllAlloc(server.allocator, std.math.maxInt(usize));
-    defer server.allocator.free(stderr_bytes);
-
-    const term = process.wait() catch |err| {
-        log.warn("Failed to await zig ast-check process, error: {}", .{err});
-        return;
-    };
-
-    if (term != .Exited) return;
-
-    var last_diagnostic: ?types.Diagnostic = null;
-    // we don't store DiagnosticRelatedInformation in last_diagnostic instead
-    // its stored in last_related_diagnostics because we need an ArrayList
-    var last_related_diagnostics: std.ArrayListUnmanaged(types.DiagnosticRelatedInformation) = .{};
-
-    // NOTE: I believe that with color off it's one diag per line; is this correct?
-    var line_iterator = std.mem.split(u8, stderr_bytes, "\n");
-
-    while (line_iterator.next()) |line| lin: {
-        if (!std.mem.startsWith(u8, line, "<stdin>")) continue;
-
-        var pos_and_diag_iterator = std.mem.split(u8, line, ":");
-        const maybe_first = pos_and_diag_iterator.next();
-        if (maybe_first) |first| {
-            if (first.len <= 1) break :lin;
-        } else break;
-
-        const utf8_position = types.Position{
-            .line = (try std.fmt.parseInt(u32, pos_and_diag_iterator.next().?, 10)) - 1,
-            .character = (try std.fmt.parseInt(u32, pos_and_diag_iterator.next().?, 10)) - 1,
-        };
-
-        // zig uses utf-8 encoding for character offsets
-        const position = offsets.convertPositionEncoding(handle.text, utf8_position, .@"utf-8", server.offset_encoding);
-        const range = offsets.tokenPositionToRange(handle.text, position, server.offset_encoding);
-
-        const msg = pos_and_diag_iterator.rest()[1..];
-
-        if (std.mem.startsWith(u8, msg, "note: ")) {
-            try last_related_diagnostics.append(allocator, .{
-                .location = .{
-                    .uri = handle.uri,
-                    .range = range,
-                },
-                .message = try server.arena.allocator().dupe(u8, msg["note: ".len..]),
-            });
-            continue;
-        }
-
-        if (last_diagnostic) |*diagnostic| {
-            diagnostic.relatedInformation = try last_related_diagnostics.toOwnedSlice(allocator);
-            try diagnostics.append(allocator, diagnostic.*);
-            last_diagnostic = null;
-        }
-
-        if (std.mem.startsWith(u8, msg, "error: ")) {
-            last_diagnostic = types.Diagnostic{
-                .range = range,
-                .severity = .Error,
-                .code = .{ .string = "ast_check" },
-                .source = "zls",
-                .message = try server.arena.allocator().dupe(u8, msg["error: ".len..]),
-            };
-        } else {
-            last_diagnostic = types.Diagnostic{
-                .range = range,
-                .severity = .Error,
-                .code = .{ .string = "ast_check" },
-                .source = "zls",
-                .message = try server.arena.allocator().dupe(u8, msg),
-            };
-        }
-    }
-
-    if (last_diagnostic) |*diagnostic| {
-        diagnostic.relatedInformation = try last_related_diagnostics.toOwnedSlice(allocator);
-        try diagnostics.append(allocator, diagnostic.*);
-        last_diagnostic = null;
-    }
-}
-
 fn getAutofixMode(server: *Server) enum {
     on_save,
     will_save_wait_until,
@@ -507,12 +229,11 @@ fn getAutofixMode(server: *Server) enum {
 /// caller owns returned memory.
 pub fn autofix(server: *Server, allocator: std.mem.Allocator, handle: *const DocumentStore.Handle) error{OutOfMemory}!std.ArrayListUnmanaged(types.TextEdit) {
     if (!server.config.enable_ast_check_diagnostics) return .{};
-
     if (handle.tree.errors.len != 0) return .{};
+
     var diagnostics = std.ArrayListUnmanaged(types.Diagnostic){};
-    getAstCheckDiagnostics(server, handle.*, &diagnostics) catch |err| {
-        log.err("failed to run ast-check: {}", .{err});
-    };
+    try diagnostics_gen.getAstCheckDiagnostics(server, handle.*, &diagnostics);
+    if (diagnostics.items.len == 0) return .{};
 
     var builder = code_actions.Builder{
         .arena = server.arena.allocator(),
@@ -765,6 +486,16 @@ fn initializeHandler(server: *Server, request: types.InitializeParams) Error!typ
         , .{server.config.record_session_path});
     }
 
+    if (server.config.enable_ast_check_diagnostics and
+        server.config.prefer_ast_check_as_child_process)
+    {
+        if (!std.process.can_spawn) {
+            log.info("'prefer_ast_check_as_child_process' is ignored because your OS can't spawn a child process", .{});
+        } else if (server.config.zig_exe_path == null) {
+            log.info("'prefer_ast_check_as_child_process' is ignored because Zig could not be found", .{});
+        }
+    }
+
     return .{
         .serverInfo = .{
             .name = "zls",
@@ -1025,7 +756,7 @@ fn openDocumentHandler(server: *Server, notification: types.DidOpenTextDocumentP
 
     if (server.client_capabilities.supports_publish_diagnostics) blk: {
         if (!std.process.can_spawn) break :blk;
-        const diagnostics = try server.generateDiagnostics(handle);
+        const diagnostics = try diagnostics_gen.generateDiagnostics(server, handle);
         server.sendNotification("textDocument/publishDiagnostics", diagnostics);
     }
 }
@@ -1042,7 +773,7 @@ fn changeDocumentHandler(server: *Server, notification: types.DidChangeTextDocum
 
     if (server.client_capabilities.supports_publish_diagnostics) blk: {
         if (!std.process.can_spawn) break :blk;
-        const diagnostics = try server.generateDiagnostics(handle.*);
+        const diagnostics = try diagnostics_gen.generateDiagnostics(server, handle.*);
         server.sendNotification("textDocument/publishDiagnostics", diagnostics);
     }
 }
@@ -1054,7 +785,7 @@ fn saveDocumentHandler(server: *Server, notification: types.DidSaveTextDocumentP
     const handle = server.document_store.getHandle(uri) orelse return;
     try server.document_store.applySave(handle);
 
-    if (std.process.can_spawn and server.getAutofixMode() == .on_save) {
+    if (server.getAutofixMode() == .on_save) {
         var text_edits = try server.autofix(allocator, handle);
 
         var workspace_edit = types.WorkspaceEdit{ .changes = .{} };
@@ -1082,7 +813,6 @@ fn willSaveWaitUntilHandler(server: *Server, request: types.WillSaveTextDocument
 
     const handle = server.document_store.getHandle(request.textDocument.uri) orelse return null;
 
-    if (!std.process.can_spawn) return null;
     var text_edits = try server.autofix(allocator, handle);
 
     return try text_edits.toOwnedSlice(allocator);
@@ -1185,7 +915,7 @@ pub fn hoverHandler(server: *Server, request: types.HoverParams) Error!?types.Ho
     // TODO: Figure out a better solution for comptime interpreter diags
     if (server.client_capabilities.supports_publish_diagnostics) blk: {
         if (!std.process.can_spawn) break :blk;
-        const diagnostics = try server.generateDiagnostics(handle.*);
+        const diagnostics = try diagnostics_gen.generateDiagnostics(server, handle.*);
         server.sendNotification("textDocument/publishDiagnostics", diagnostics);
     }
 
@@ -1459,12 +1189,8 @@ fn codeActionHandler(server: *Server, request: types.CodeActionParams) Error!?[]
 
     // as of right now, only ast-check errors may get a code action
     var diagnostics = std.ArrayListUnmanaged(types.Diagnostic){};
-    if (server.config.enable_ast_check_diagnostics and handle.tree.errors.len == 0) blk: {
-        if (!std.process.can_spawn) break :blk;
-        getAstCheckDiagnostics(server, handle.*, &diagnostics) catch |err| {
-            log.err("failed to run ast-check: {}", .{err});
-            return error.InternalError;
-        };
+    if (server.config.enable_ast_check_diagnostics and handle.tree.errors.len == 0) {
+        try diagnostics_gen.getAstCheckDiagnostics(server, handle.*, &diagnostics);
     }
 
     var actions = std.ArrayListUnmanaged(types.CodeAction){};
diff --git a/src/config_gen/config.json b/src/config_gen/config.json
index 3ac4b16..2b4821d 100644
--- a/src/config_gen/config.json
+++ b/src/config_gen/config.json
@@ -107,6 +107,12 @@
             "type": "usize",
             "default": "1048576"
         },
+        {
+            "name": "prefer_ast_check_as_child_process",
+            "description": "Can be used in conjuction with `enable_ast_check_diagnostics` to favor using `zig ast-check` instead of ZLS's fork",
+            "type": "bool",
+            "default": "true"
+        },
         {
             "name": "record_session",
             "description": "When true, zls will record all request is receives and write in into `record_session_path`, so that they can replayed with `zls replay`",
diff --git a/src/features/diagnostics.zig b/src/features/diagnostics.zig
new file mode 100644
index 0000000..6603cd9
--- /dev/null
+++ b/src/features/diagnostics.zig
@@ -0,0 +1,391 @@
+const std = @import("std");
+const Ast = std.zig.Ast;
+const log = std.log.scoped(.zls_diagnostics);
+
+const Server = @import("../Server.zig");
+const DocumentStore = @import("../DocumentStore.zig");
+const types = @import("../lsp.zig");
+const Analyser = @import("../analysis.zig");
+const ast = @import("../ast.zig");
+const offsets = @import("../offsets.zig");
+const tracy = @import("../tracy.zig");
+
+const Module = @import("../stage2/Module.zig");
+const Zir = @import("../stage2/Zir.zig");
+
+pub fn generateDiagnostics(server: *Server, handle: DocumentStore.Handle) error{OutOfMemory}!types.PublishDiagnosticsParams {
+    const tracy_zone = tracy.trace(@src());
+    defer tracy_zone.end();
+
+    std.debug.assert(server.client_capabilities.supports_publish_diagnostics);
+
+    const tree = handle.tree;
+
+    var allocator = server.arena.allocator();
+    var diagnostics = std.ArrayListUnmanaged(types.Diagnostic){};
+
+    for (tree.errors) |err| {
+        var mem_buffer: [256]u8 = undefined;
+        var fbs = std.io.fixedBufferStream(&mem_buffer);
+        tree.renderError(err, fbs.writer()) catch if (std.debug.runtime_safety) unreachable else continue; // if an error occurs here increase buffer size
+
+        try diagnostics.append(allocator, .{
+            .range = offsets.tokenToRange(tree, err.token, server.offset_encoding),
+            .severity = .Error,
+            .code = .{ .string = @tagName(err.tag) },
+            .source = "zls",
+            .message = try server.arena.allocator().dupe(u8, fbs.getWritten()),
+            // .relatedInformation = undefined
+        });
+    }
+
+    if (server.config.enable_ast_check_diagnostics and tree.errors.len == 0) {
+        try getAstCheckDiagnostics(server, handle, &diagnostics);
+    }
+
+    if (server.config.warn_style) {
+        var node: u32 = 0;
+        while (node < tree.nodes.len) : (node += 1) {
+            if (ast.isBuiltinCall(tree, node)) {
+                const builtin_token = tree.nodes.items(.main_token)[node];
+                const call_name = tree.tokenSlice(builtin_token);
+
+                if (!std.mem.eql(u8, call_name, "@import")) continue;
+
+                var buffer: [2]Ast.Node.Index = undefined;
+                const params = ast.builtinCallParams(tree, node, &buffer).?;
+
+                if (params.len != 1) continue;
+
+                const import_str_token = tree.nodes.items(.main_token)[params[0]];
+                const import_str = tree.tokenSlice(import_str_token);
+
+                if (std.mem.startsWith(u8, import_str, "\"./")) {
+                    try diagnostics.append(allocator, .{
+                        .range = offsets.tokenToRange(tree, import_str_token, server.offset_encoding),
+                        .severity = .Hint,
+                        .code = .{ .string = "dot_slash_import" },
+                        .source = "zls",
+                        .message = "A ./ is not needed in imports",
+                    });
+                }
+            }
+        }
+
+        // TODO: style warnings for types, values and declarations below root scope
+        if (tree.errors.len == 0) {
+            for (tree.rootDecls()) |decl_idx| {
+                const decl = tree.nodes.items(.tag)[decl_idx];
+                switch (decl) {
+                    .fn_proto,
+                    .fn_proto_multi,
+                    .fn_proto_one,
+                    .fn_proto_simple,
+                    .fn_decl,
+                    => blk: {
+                        var buf: [1]Ast.Node.Index = undefined;
+                        const func = tree.fullFnProto(&buf, decl_idx).?;
+                        if (func.extern_export_inline_token != null) break :blk;
+
+                        if (func.name_token) |name_token| {
+                            const is_type_function = Analyser.isTypeFunction(tree, func);
+
+                            const func_name = tree.tokenSlice(name_token);
+                            if (!is_type_function and !Analyser.isCamelCase(func_name)) {
+                                try diagnostics.append(allocator, .{
+                                    .range = offsets.tokenToRange(tree, name_token, server.offset_encoding),
+                                    .severity = .Hint,
+                                    .code = .{ .string = "bad_style" },
+                                    .source = "zls",
+                                    .message = "Functions should be camelCase",
+                                });
+                            } else if (is_type_function and !Analyser.isPascalCase(func_name)) {
+                                try diagnostics.append(allocator, .{
+                                    .range = offsets.tokenToRange(tree, name_token, server.offset_encoding),
+                                    .severity = .Hint,
+                                    .code = .{ .string = "bad_style" },
+                                    .source = "zls",
+                                    .message = "Type functions should be PascalCase",
+                                });
+                            }
+                        }
+                    },
+                    else => {},
+                }
+            }
+        }
+    }
+
+    for (handle.cimports.items(.hash), handle.cimports.items(.node)) |hash, node| {
+        const result = server.document_store.cimports.get(hash) orelse continue;
+        if (result != .failure) continue;
+        const stderr = std.mem.trim(u8, result.failure, " ");
+
+        var pos_and_diag_iterator = std.mem.split(u8, stderr, ":");
+        _ = pos_and_diag_iterator.next(); // skip file path
+        _ = pos_and_diag_iterator.next(); // skip line
+        _ = pos_and_diag_iterator.next(); // skip character
+
+        try diagnostics.append(allocator, .{
+            .range = offsets.nodeToRange(handle.tree, node, server.offset_encoding),
+            .severity = .Error,
+            .code = .{ .string = "cImport" },
+            .source = "zls",
+            .message = try allocator.dupe(u8, pos_and_diag_iterator.rest()),
+        });
+    }
+
+    if (server.config.highlight_global_var_declarations) {
+        const main_tokens = tree.nodes.items(.main_token);
+        const tags = tree.tokens.items(.tag);
+        for (tree.rootDecls()) |decl| {
+            const decl_tag = tree.nodes.items(.tag)[decl];
+            const decl_main_token = tree.nodes.items(.main_token)[decl];
+
+            switch (decl_tag) {
+                .simple_var_decl,
+                .aligned_var_decl,
+                .local_var_decl,
+                .global_var_decl,
+                => {
+                    if (tags[main_tokens[decl]] != .keyword_var) continue; // skip anything immutable
+                    // uncomment this to get a list :)
+                    //log.debug("possible global variable \"{s}\"", .{tree.tokenSlice(decl_main_token + 1)});
+                    try diagnostics.append(allocator, .{
+                        .range = offsets.tokenToRange(tree, decl_main_token, server.offset_encoding),
+                        .severity = .Hint,
+                        .code = .{ .string = "highlight_global_var_declarations" },
+                        .source = "zls",
+                        .message = "Global var declaration",
+                    });
+                },
+                else => {},
+            }
+        }
+    }
+
+    if (handle.interpreter) |int| {
+        try diagnostics.ensureUnusedCapacity(allocator, int.errors.count());
+
+        var err_it = int.errors.iterator();
+
+        while (err_it.next()) |err| {
+            diagnostics.appendAssumeCapacity(.{
+                .range = offsets.nodeToRange(tree, err.key_ptr.*, server.offset_encoding),
+                .severity = .Error,
+                .code = .{ .string = err.value_ptr.code },
+                .source = "zls",
+                .message = err.value_ptr.message,
+            });
+        }
+    }
+    // try diagnostics.appendSlice(allocator, handle.interpreter.?.diagnostics.items);
+
+    return .{
+        .uri = handle.uri,
+        .diagnostics = diagnostics.items,
+    };
+}
+
+pub fn getAstCheckDiagnostics(
+    server: *Server,
+    handle: DocumentStore.Handle,
+    diagnostics: *std.ArrayListUnmanaged(types.Diagnostic),
+) error{OutOfMemory}!void {
+    std.debug.assert(server.config.enable_ast_check_diagnostics);
+    std.debug.assert(handle.tree.errors.len == 0);
+
+    if (server.config.prefer_ast_check_as_child_process and
+        std.process.can_spawn and
+        server.config.zig_exe_path != null)
+    {
+        getDiagnosticsFromAstCheck(server, handle, diagnostics) catch |err| {
+            log.err("failed to run ast-check: {}", .{err});
+        };
+    } else {
+        std.debug.assert(server.document_store.wantZir());
+        switch (handle.zir_status) {
+            .none, .outdated => {},
+            .done => try getDiagnosticsFromZir(server, handle, diagnostics),
+        }
+    }
+}
+
+fn getDiagnosticsFromAstCheck(
+    server: *Server,
+    handle: DocumentStore.Handle,
+    diagnostics: *std.ArrayListUnmanaged(types.Diagnostic),
+) !void {
+    comptime std.debug.assert(std.process.can_spawn);
+    std.debug.assert(server.config.zig_exe_path != null);
+    var allocator = server.arena.allocator();
+
+    const zig_exe_path = server.config.zig_exe_path.?;
+
+    var process = std.ChildProcess.init(&[_][]const u8{ zig_exe_path, "ast-check", "--color", "off" }, server.allocator);
+    process.stdin_behavior = .Pipe;
+    process.stderr_behavior = .Pipe;
+
+    process.spawn() catch |err| {
+        log.warn("Failed to spawn zig ast-check process, error: {}", .{err});
+        return;
+    };
+    try process.stdin.?.writeAll(handle.text);
+    process.stdin.?.close();
+
+    process.stdin = null;
+
+    const stderr_bytes = try process.stderr.?.reader().readAllAlloc(server.allocator, std.math.maxInt(usize));
+    defer server.allocator.free(stderr_bytes);
+
+    const term = process.wait() catch |err| {
+        log.warn("Failed to await zig ast-check process, error: {}", .{err});
+        return;
+    };
+
+    if (term != .Exited) return;
+
+    var last_diagnostic: ?types.Diagnostic = null;
+    // we don't store DiagnosticRelatedInformation in last_diagnostic instead
+    // its stored in last_related_diagnostics because we need an ArrayList
+    var last_related_diagnostics: std.ArrayListUnmanaged(types.DiagnosticRelatedInformation) = .{};
+
+    // NOTE: I believe that with color off it's one diag per line; is this correct?
+    var line_iterator = std.mem.split(u8, stderr_bytes, "\n");
+
+    while (line_iterator.next()) |line| lin: {
+        if (!std.mem.startsWith(u8, line, "<stdin>")) continue;
+
+        var pos_and_diag_iterator = std.mem.split(u8, line, ":");
+        const maybe_first = pos_and_diag_iterator.next();
+        if (maybe_first) |first| {
+            if (first.len <= 1) break :lin;
+        } else break;
+
+        const utf8_position = types.Position{
+            .line = (try std.fmt.parseInt(u32, pos_and_diag_iterator.next().?, 10)) - 1,
+            .character = (try std.fmt.parseInt(u32, pos_and_diag_iterator.next().?, 10)) - 1,
+        };
+
+        // zig uses utf-8 encoding for character offsets
+        const position = offsets.convertPositionEncoding(handle.text, utf8_position, .@"utf-8", server.offset_encoding);
+        const range = offsets.tokenPositionToRange(handle.text, position, server.offset_encoding);
+
+        const msg = pos_and_diag_iterator.rest()[1..];
+
+        if (std.mem.startsWith(u8, msg, "note: ")) {
+            try last_related_diagnostics.append(allocator, .{
+                .location = .{
+                    .uri = handle.uri,
+                    .range = range,
+                },
+                .message = try server.arena.allocator().dupe(u8, msg["note: ".len..]),
+            });
+            continue;
+        }
+
+        if (last_diagnostic) |*diagnostic| {
+            diagnostic.relatedInformation = try last_related_diagnostics.toOwnedSlice(allocator);
+            try diagnostics.append(allocator, diagnostic.*);
+            last_diagnostic = null;
+        }
+
+        if (std.mem.startsWith(u8, msg, "error: ")) {
+            last_diagnostic = types.Diagnostic{
+                .range = range,
+                .severity = .Error,
+                .code = .{ .string = "ast_check" },
+                .source = "zls",
+                .message = try server.arena.allocator().dupe(u8, msg["error: ".len..]),
+            };
+        } else {
+            last_diagnostic = types.Diagnostic{
+                .range = range,
+                .severity = .Error,
+                .code = .{ .string = "ast_check" },
+                .source = "zls",
+                .message = try server.arena.allocator().dupe(u8, msg),
+            };
+        }
+    }
+
+    if (last_diagnostic) |*diagnostic| {
+        diagnostic.relatedInformation = try last_related_diagnostics.toOwnedSlice(allocator);
+        try diagnostics.append(allocator, diagnostic.*);
+        last_diagnostic = null;
+    }
+}
+
+fn getDiagnosticsFromZir(
+    server: *Server,
+    handle: DocumentStore.Handle,
+    diagnostics: *std.ArrayListUnmanaged(types.Diagnostic),
+) error{OutOfMemory}!void {
+    std.debug.assert(handle.zir_status != .none);
+
+    const allocator = server.arena.allocator();
+
+    const payload_index = handle.zir.extra[@enumToInt(Zir.ExtraIndex.compile_errors)];
+    if (payload_index == 0) return;
+
+    const header = handle.zir.extraData(Zir.Inst.CompileErrors, payload_index);
+    const items_len = header.data.items_len;
+
+    try diagnostics.ensureUnusedCapacity(allocator, items_len);
+
+    var extra_index = header.end;
+    for (0..items_len) |_| {
+        const item = handle.zir.extraData(Zir.Inst.CompileErrors.Item, extra_index);
+        extra_index = item.end;
+        const err_loc = blk: {
+            if (item.data.node != 0) {
+                break :blk offsets.nodeToLoc(handle.tree, item.data.node);
+            }
+            const loc = offsets.tokenToLoc(handle.tree, item.data.token);
+            break :blk offsets.Loc{
+                .start = loc.start + item.data.byte_offset,
+                .end = loc.end,
+            };
+        };
+
+        var notes: []types.DiagnosticRelatedInformation = &.{};
+        if (item.data.notes != 0) {
+            const block = handle.zir.extraData(Zir.Inst.Block, item.data.notes);
+            const body = handle.zir.extra[block.end..][0..block.data.body_len];
+            notes = try allocator.alloc(types.DiagnosticRelatedInformation, body.len);
+            for (notes, body) |*note, note_index| {
+                const note_item = handle.zir.extraData(Zir.Inst.CompileErrors.Item, note_index);
+                const msg = handle.zir.nullTerminatedString(note_item.data.msg);
+
+                const loc = blk: {
+                    if (note_item.data.node != 0) {
+                        break :blk offsets.nodeToLoc(handle.tree, note_item.data.node);
+                    }
+                    const loc = offsets.tokenToLoc(handle.tree, note_item.data.token);
+                    break :blk offsets.Loc{
+                        .start = loc.start + note_item.data.byte_offset,
+                        .end = loc.end,
+                    };
+                };
+
+                note.* = .{
+                    .location = .{
+                        .uri = handle.uri,
+                        .range = offsets.locToRange(handle.text, loc, server.offset_encoding),
+                    },
+                    .message = msg,
+                };
+            }
+        }
+
+        const msg = handle.zir.nullTerminatedString(item.data.msg);
+        diagnostics.appendAssumeCapacity(.{
+            .range = offsets.locToRange(handle.text, err_loc, server.offset_encoding),
+            .severity = .Error,
+            .code = .{ .string = "ast_check" },
+            .source = "zls",
+            .message = msg,
+            .relatedInformation = if (notes.len != 0) notes else null,
+        });
+    }
+}