Android RTL layout verification

android:supportsRtl="true" is usually declared on day one and never exercised. Verifying it is easy to get wrong: the two most obvious ways to force RTL both fail silently, and the sweep then measures an LTR layout while reporting "no problems".

The rule

Never report an RTL result without first proving the layout actually mirrored. Absence of defects in a configuration you failed to enter is not evidence.

Trap 1 — developer options force_rtl does nothing

adb shell settings put global debug.force_rtl 1

Writes the setting, readback confirms it, app relaunches — and positions are byte-identical to LTR. It does not apply to a freshly launched app the way the Settings toggle does.

Trap 2 — per-app locale is filtered against shipped locales

adb shell cmd locale set-app-locales com.example.app --locales ar-XB
adb shell cmd locale get-app-locales com.example.app   # confirms [ar-XB]

The readback lies about the effect: per-app locales are resolved against the locales the APK actually contains. If the build ships no ar-XB resources the request falls back to the default locale, and the app runs LTR in English.

Fix — ship the pseudolocale resources in debug builds:

buildTypes {
    debug {
        isPseudoLocalesEnabled = true   // adds en-XA / ar-XB resources
    }
}

The control that settles it

Capture one screen's element positions in each state and require movement:

def snap():                       # force-stop, launch, uiautomator dump
    ...                           # -> {text: (x1, x2)}

adb shell cmd locale set-app-locales <pkg> --locales ""      # LTR
ltr = snap()
adb shell cmd locale set-app-locales <pkg> --locales ar-XB   # RTL
rtl = snap()
assert any(ltr[k] != rtl[k] for k in shared_keys)            # else: not RTL

A genuine flip looks like HUNTER ltr=(195,479) rtl=(601,885). Identical tuples mean you are still in LTR — stop and fix the configuration.

The sweep, once RTL is proven live

Per destination, from the uiautomator dump:

• off-screen: any text node with x1 < 0 or x2 > screen_width
• squished: len(text) > 3 and width < 90 and height > 2 * width (the one-letter-per-line shape)
• crash buffer empty (adb shell logcat -d -b crash)

Static audit alongside it — these are the APIs that break mirroring, and zero hits is a meaningful result because Compose's start/end modifiers mirror automatically:

AbsoluteAlignment | Alignment.(Top|Bottom|Center)(Left|Right)
TextAlign.(Left|Right) | absolutePadding | absoluteOffset

Limit worth stating rather than hiding

en-XA (the expansion pseudolocale) only expands resource strings. If the UI uses Kotlin string literals, en-XA changes nothing and cannot test text expansion. Say so, and cover expansion with the font-scale axis (1.5×/2.0×) instead of implying pseudolocale coverage you do not have.

Restore the device afterwards

adb shell cmd locale set-app-locales <pkg> --locales ""
adb shell settings put global debug.force_rtl 0