Running and debugging

Run

go tool nsgo dev

dev builds the app for this machine and opens it, or for the target nsgo.yaml’s dev.target names. On each save of a Go file it rebuilds and restarts the app, running go mod tidy first when the app imports a package whose module go.mod or go.sum lacks; a change of TSX alone updates the running app in place, keeping its state. The run ends with the app.

-target runs it elsewhere, and -device picks the iPhone, Apple TV, Apple Watch, simulator or Android device by name, UDID or serial:

go tool nsgo dev -target web                # in the browser, at -port (8080 by default)
go tool nsgo dev -target ios_simulator      # in the iOS simulator
go tool nsgo dev -target ios                # on the connected iPhone, signed by Xcode
go tool nsgo dev -target tvos_simulator     # in the Apple TV simulator
go tool nsgo dev -target watchos_simulator  # in the Apple Watch simulator
go tool nsgo dev -target android            # on a connected device or emulator, over adb

-h lists every flag.

Errors

A failed build shows over the running app, with buttons to copy the error and to build again; fix the file and the next save replaces it. A component that panics while it renders shows the same way. The app’s own output, such as log.Print, appears in the terminal under the tool’s lines.

Before running, go tool nsgo check vets the app and type-checks its TSX; -target all vets it for every target, so code behind another platform’s build tags is checked from a Mac too.

Updates

go tool nsgo dev -trace

-trace prints each commit of the running app: its number, its time, and the mount items it sent, so you see which views an update created, changed or removed. A signal change that updates more than you expect shows up here first. go tool nsgo test -trace prints the same under each step of a test.

Speed

go tool nsgo dev -fps
go tool nsgo dev -release -fps

-fps shows the performance monitor over the app on macOS, iOS, Windows and Linux: what its frames and commits cost while it runs. Dev builds carry the dev client; measure with -release, which builds as nsgo build does.

Languages and appearance

go tool nsgo dev -lang zh-Hans
go tool nsgo dev -lang en-XA   # accented and longer, to find untranslated and cut text
go tool nsgo dev -lang ar-XB   # right to left

-lang starts the app in a locale, a pseudo locale too (Localization).

Flags of every build

Every build of an app, packages included, takes NSGo’s own flags as it starts, which override nsgo.yaml and the app’s code and never reach the app’s own flags:

Flag	Effect
--nsgo-fps	Shows the performance monitor on macOS, iOS, Windows and Linux
--nsgo-lang=zh-Hans	Starts the app in a locale, a pseudo locale too
--nsgo-appearance=dark	Starts the app light, dark or following the system

./Hello --nsgo-fps                                   # Windows and Linux
open Hello.app --args --nsgo-fps                     # macOS
xcrun simctl launch booted dev.example.hello --nsgo-fps
adb shell am start -n dev.example.hello/dev.oneo.nsgo.NsgoActivity --ez nsgo-fps true --es nsgo-lang de

On the web they go in the page’s query: ?nsgo-fps&nsgo-lang=de.