feat: add configurable UCE error pages

src/lib/compiler.cpp

@@ -18,7 +18,7 @@ const char* UCE_CLI_SYMBOL = "__uce_cli";
 const char* UCE_SERVE_HTTP_SYMBOL = "__uce_serve_http";
 const char* UCE_ONCE_SYMBOL = "__uce_once";
 const char* UCE_INIT_SYMBOL = "__uce_init";
-const u64 UCE_UNIT_ABI_VERSION = 4;
+const u64 UCE_UNIT_ABI_VERSION = 5;
 
 struct SharedUnitFilesystemState
 {
@@ -995,6 +995,15 @@ SharedUnit* compiler_load_shared_unit(Request* context, String file_name, String
 		printf("%s\n", display_messages.c_str());
 		if(compiler_can_write_response(context) && context->stats.invoke_count == 1)
 		{
+			DTree error_info;
+			error_info["type"] = "compiler_error";
+			error_info["status"] = su->compile_status;
+			error_info["source"] = su->file_name;
+			error_info["compiler_output"] = su->compiler_messages;
+			error_info["generated_cpp"] = compiler_generated_cpp_path(su);
+			error_info["details"] = display_messages;
+			if(compiler_render_error_page(context, "page_compiler_error", 500, "UCE Unit Compile Error", error_info))
+				return(0);
 			context->set_status(500, "UCE Unit Compile Error");
 			context->header["Content-Type"] = "text/plain; charset=utf-8";
 		}
@@ -1739,9 +1748,106 @@ bool compiler_invoke_component(Request* context, String file_name, String render
 	));
 }
 
+String compiler_error_page_unit(Request* context, String config_key)
+{
+	if(!context || !context->server)
+		return("");
+	String configured = trim(first(
+		context->server->config[config_key],
+		context->server->config[to_upper(config_key)]
+	));
+	if(configured == "")
+		return("");
+	// Resolve relative to where the server was started, not the volatile
+	// per-unit working directory (which is also stale right after a fault).
+	String resolved = compiler_resolve_unit_path(context, configured, process_start_directory());
+	if(resolved == "" || !file_exists(resolved))
+		return("");
+	return(resolved);
+}
+
+bool compiler_render_error_page(Request* context, String config_key, s32 status_code, String status_reason, DTree error_info)
+{
+	if(!compiler_can_write_response(context))
+		return(false);
+	if(!context->server || context->resources.error_page_active)
+		return(false);
+	String unit_file = compiler_error_page_unit(context, config_key);
+	if(unit_file == "")
+		return(false);
+
+	String previous_response_code = context->response_code;
+	s32 previous_status = context->flags.status;
+	String previous_content_type = context->header["Content-Type"];
+
+	context->resources.error_page_active = true;
+	context->call["error"] = error_info;
+	context->set_status(status_code, status_reason);
+	context->header["Content-Type"] = first(context->server->config["CONTENT_TYPE"], "text/html; charset=utf-8");
+
+	ob_start();
+	String error_message = "";
+	bool rendered = compiler_invoke_render(context, unit_file, "render", &error_message);
+	String html = ob_get_close();
+	context->resources.error_page_active = false;
+
+	if(!rendered)
+	{
+		printf("(!) configured %s page %s failed to render: %s\n", config_key.c_str(), unit_file.c_str(), trim(error_message).c_str());
+		context->response_code = previous_response_code;
+		context->flags.status = previous_status;
+		context->header["Content-Type"] = previous_content_type;
+		context->call.remove("error");
+		return(false);
+	}
+	print(html);
+	return(true);
+}
+
+bool compiler_unit_compile_pending(Request* context, String file_name)
+{
+	String normalized = compiler_normalize_unit_path(context, file_name);
+	if(normalized == "" || !file_exists(normalized))
+		return(false);
+	if(compiler_reusable_cached_unit(context, normalized, false, false))
+		return(false);
+
+	SharedUnit probe;
+	setup_unit_paths(context, &probe, normalized);
+	auto state = inspect_shared_unit_filesystem(context, &probe);
+	if(!shared_unit_compile_check(state).needs_compile)
+		return(false);
+	// A persisted, still-current failure is a compiler error, not a build in
+	// progress: let the load path surface it.
+	if(compiler_failure_retry_deferred(context, &probe, state))
+		return(false);
+	return(true);
+}
+
 void compiler_invoke(Request* context, String file_name)
 {
 	printf("(i) compiler_invoke file %s\n", file_name.c_str());
+
+	// Entry-unit hook for the configured "compiling" page: when the unit needs
+	// a (re)build that the proactive compiler can deliver, answer immediately
+	// instead of blocking the worker on a synchronous compile.
+	if(context && context->stats.invoke_count == 0 &&
+		!context->resources.is_cli && !context->resources.error_page_active &&
+		config_bool("PROACTIVE_COMPILE_ENABLED", true) &&
+		compiler_error_page_unit(context, "page_compiling") != "")
+	{
+		String resolved = compiler_resolve_unit_path(context, file_name, "");
+		if(resolved != "" && compiler_unit_compile_pending(context, resolved))
+		{
+			compiler_track_known_unit(context, resolved);
+			DTree error_info;
+			error_info["type"] = "compiling";
+			error_info["source"] = resolved;
+			if(compiler_render_error_page(context, "page_compiling", 503, "UCE Unit Compiling", error_info))
+				return;
+		}
+	}
+
 	String error_message = "";
 	if(!compiler_invoke_render(context, file_name, "render", &error_message) && error_message != "")
 	{

src/lib/compiler.h

@@ -21,6 +21,9 @@ void compiler_invoke_websocket(Request* context, String file_name);
 void compiler_invoke_cli(Request* context, String file_name);
 void compiler_invoke_serve_http(Request* context, String file_name, String handler_name = "");
 SharedUnit* compiler_load_shared_unit(Request* context, String file_name, String current_path = "", bool opt_so_optional = false);
+String compiler_error_page_unit(Request* context, String config_key);
+bool compiler_render_error_page(Request* context, String config_key, s32 status_code, String status_reason, DTree error_info);
+bool compiler_unit_compile_pending(Request* context, String file_name);
 String compiler_site_directory(Request* context);
 StringList compiler_scan_site_units(Request* context);
 StringList compiler_list_known_units(Request* context);

src/lib/sys.cpp

@@ -348,6 +348,15 @@ String cwd_get()
 	return(std::filesystem::current_path());
 }
 
+String process_start_directory()
+{
+	// Primed in main() before any unit handler can chdir; fault recovery and
+	// config-relative path resolution anchor to this instead of the volatile
+	// per-unit working directory.
+	static String start_directory = cwd_get();
+	return(start_directory);
+}
+
 void cwd_set(String path)
 {
 	chdir(path.c_str());

src/lib/sys.h

@@ -30,6 +30,7 @@ bool file_append(String file_name, Ts... args)
 }
 String cwd_get();
 void cwd_set(String path);
+String process_start_directory();
 time_t file_mtime(String file_name);
 void file_unlink(String file_name);
 String expand_path(String path, String relative_to_path = "");

src/lib/types.h

@@ -224,6 +224,10 @@ struct Request {
 		bool websocket_is_text = false;
 		String current_unit_file = "";
 		String params_buffer;
+		// True while a configured error page (page_compiling /
+		// page_compiler_error / page_runtime_error) is rendering, so a failing
+		// error page can never recurse into another error page.
+		bool error_page_active = false;
 	} resources;
 
 	void ob_start();