Use ML Kit's barcode scanning API without Firebase dependencies or datatransport stuff

Gradle

Before

dependencies {
    implementation("com.google.mlkit:barcode-scanning:17.3.0")
}

After

dependencies {
    implementation("com.google.android.gms:play-services-basement:18.4.0")
    implementation("com.google.mlkit:barcode-scanning:17.3.0") {
        isTransitive = false
    }
}

Code

import android.content.Context
import android.graphics.Bitmap
import android.graphics.Point
import android.os.Parcel
import android.os.Parcelable
import com.google.android.gms.common.internal.safeparcel.SafeParcelReader
import com.google.android.gms.dynamic.ObjectWrapper
import com.google.mlkit.vision.barcode.bundled.internal.ThickBarcodeScannerCreator


private typealias BarcodeScannerOptions = com.google.android.gms.internal.mlkit_vision_barcode_bundled.zzba
private typealias ImageMetadata = com.google.android.gms.internal.mlkit_vision_barcode_bundled.zzcc
typealias BarcodeScanner = com.google.android.gms.internal.mlkit_vision_barcode_bundled.zzbn
private typealias Barcode = com.google.android.gms.internal.mlkit_vision_barcode_bundled.zzay

fun createBarcodeScanner(
    context: Context,
    // https://developers.google.com/android/reference/com/google/mlkit/vision/barcode/common/Barcode#FORMAT_ALL_FORMATS
    format: Int, // 0 for all format
): BarcodeScanner {
    return ThickBarcodeScannerCreator().newBarcodeScanner(
        ObjectWrapper.wrap(context.applicationContext),
        BarcodeScannerOptions(format, true)
    ).also { it.zzd() }
}

// Reminder: don't invoke this after close
private fun BarcodeScanner.recognize0(image: Bitmap): List<Barcode> {
    return zzb(
        ObjectWrapper.wrap(image),
        ImageMetadata(
            /** -1 for [Bitmap], 35 for [Image] */
            -1,
            image.width,
            image.height,
            /** rotation value */
            0,
            /** timestamp, 0 is OK */
            System.currentTimeMillis()
        )
    ).filterIsInstance<Barcode>()
}

fun BarcodeScanner.close() {
    zzf()
}

class BarcodeData(
    val format: Int,
    val rawValue: String?,
    val cornerPoints: Array<Point>?,
)

fun BarcodeScanner.recognize(image: Bitmap): List<BarcodeData> {
    return recognize0(image).mapNotNull(::readBarcodeResult)
}

// Access private fields without reflection
private fun readBarcodeResult(data: Barcode): BarcodeData? {
    val parcel = Parcel.obtain()
    data.writeToParcel(parcel, Parcelable.PARCELABLE_WRITE_RETURN_VALUE)

    // read it back
    parcel.setDataPosition(0)
    var format = 0
    var rawValue: String? = null
    var cornerPoints: Array<Point>? = null
    SafeParcelReader.validateObjectHeader(parcel).let { header ->
        while (parcel.dataPosition() < header) {
            val h = SafeParcelReader.readHeader(parcel)
            when (SafeParcelReader.getFieldId(h)) {
                1 -> {
                    val f = SafeParcelReader.readInt(parcel, h)
                    // unrecognized format
                    if (f < 1) {
                        parcel.recycle()
                        return null
                    }
                    format = f
                }

                3 -> rawValue = SafeParcelReader.createString(parcel, h)
                5 -> cornerPoints = SafeParcelReader.createTypedArray(parcel, h, Point.CREATOR)
                else -> SafeParcelReader.skipUnknownField(parcel, h)
            }
        }
        SafeParcelReader.ensureAtEnd(parcel, header)
    }

    parcel.recycle()
    return if (format < 1) null else BarcodeData(
        format = format,
        rawValue = rawValue,
        cornerPoints = cornerPoints,
    )
}

Almost done

Add missing class to java src directory. ProGuard will remove it.

package com.google.mlkit.vision.common.internal;

public class ImageUtils {
    private static final ImageUtils s = new ImageUtils();

    public static ImageUtils getInstance() {
        return s;
    }

    public android.graphics.Matrix getUprightRotationMatrix(int width, int height, int rotation) {
        // assert rotation is 0
        return null;
    }
}

Add ProGuard rules from com.google.mlkit:common:18.10.0.

# Annotations are implemented as attributes, so we have to explicitly keep them.
# Catch all which encompasses attributes like RuntimeVisibleParameterAnnotations
# and RuntimeVisibleTypeAnnotations
-keepattributes RuntimeVisible*Annotation*

# JNI is an entry point that's hard to keep track of, so there's
# an annotation to mark fields and methods used by native code.

# Keep the annotations that proguard needs to process.
-keep class com.google.android.apps.common.proguard.UsedBy*

# Just because native code accesses members of a class, does not mean that the
# class itself needs to be annotated - only annotate classes that are
# referenced themselves in native code.
-keep @com.google.android.apps.common.proguard.UsedBy* class * {
  <init>();
}
-keepclassmembers class * {
    @com.google.android.apps.common.proguard.UsedBy* *;
}