React Native - Automatic version name from package.json to android build manifest

While the currently accepted answer will work, there is a much simpler, and therefore more reliable way to do it. You can actually read the value set in package.json right from build.gradle.

Modify your android/app/build.gradle:

// On top of your file import a JSON parser
import groovy.json.JsonSlurper

// Create an easy to use function
def getVersionFromNpm() {
    //  Read and parse package.json file from project root
    def inputFile = new File("$rootDir/../package.json")
    def packageJson = new JsonSlurper().parseText(inputFile.text)

    // Return the version, you can get any value this way
    return packageJson["version"]
}

android {
    defaultConfig {
        applicationId "your.app.id"
        versionName getVersionFromNpm()
    }
}

This way you won't need a pre-build script or anything, it will just work.

Since I was working with this for several days, I decided to share with everyone how I did it, because it could help others.

Tools used:

1. GitVersion: We will use GitVersion to generate a semantic version automatically depending on many factors like current branch, tags, commits, etc. The toold does an excellent job and you can forget about naming your versions. Of course, if you set a tag to a commit, it will use that tag as name.
2. PowerShell: This command line OS built by Microsoft has the ability to be run from Mac, Linux or Windows, and I chose it because the builds can be agnostic of the OS version. For example I develop on Windows but the build machine has MacOS.

Edit App build.gradle

The app gradle only needs one line added at the end of it. In my case I have the Google Play Services gradle and I added it after that.

apply from: 'version.gradle'

version.gradle

This file should be in the same folder as your app gradle and this is the content:

task updatePackage(type: Exec, description: 'Updating package.json') {
    commandLine 'powershell', ' -command ' , '$semver=(gitversion /showvariable Semver); Set-Content -path version.properties -value semver=$semver; npm version --no-git-tag-version --allow-same-version $semver'  
}
preBuild.dependsOn updatePackage

task setVariantVersion {

    doLast {

        if (plugins.hasPlugin('android') || plugins.hasPlugin('android-library')) {

            def autoIncrementVariant = { variant ->
                variant.mergedFlavor.versionName = calculateVersionName()
            }

            if (plugins.hasPlugin('android')){
                //Fails without putting android. first
                android.applicationVariants.all { variant -> autoIncrementVariant(variant) }
            }

            if (plugins.hasPlugin('android-library')) {
                //Probably needs android-library before libraryVariants. Needs testing
                libraryVariants.all { variant -> autoIncrementVariant(variant) }
            }
        }

    }

}
preBuild.dependsOn setVariantVersion
setVariantVersion.mustRunAfter updatePackage

ext {
    versionFile = new File('version.properties')
    calculateVersionName = {
        def version = readVersion()
        def semver = "Unknown"
        if (version != null){
            semver = version.getProperty('semver')
        }
        return semver
    }
}

Properties readVersion() {
    //It gets called once for every variant but all get the same version
    def version = new Properties()
    try {
        file(versionFile).withInputStream { version.load(it) }
    } catch (Exception error) {
        version = null
    } 
    return version
}

Now, let's review what the script is actually doing:

1. updatePackage: This task runs at the very beginning of your build (actually before preBuild) and it executes gitversion to get the current version and then creates a version.properties file which later be read by gradle to take the version.
2. setVariantVersion: This is called afterEvaluate on every variant. Meaning that if you have multiple builds like debug, release, qa, staging, etc, all will get the same version. For my use case this is fine, but you might want to tweak this.
3. Task Order: One thing that bothered me was that the version was being run before the file was generated. This is fixed by using the mustRunAfter tag.

PowerShell Script Explained

This is the script that gets run first. Let's review what is doing:

$semver=(gitversion /showvariable Semver);
Set-Content -path props.properties -value semver=$semver; 
npm version --no-git-tag-version --allow-same-version $semver

1. Line 1: gitversion has multiple type of versions. If you run it without any parameter you will get a json file with many variants. Here we are saying that we only want the SemVer. (See also FullSemVer)
2. Line 2: PowerShell way to create a file and save the contents to it. This can be also made with > but I had encoding issues and the properties file was not being read.
3. Line 3: This line updates your package.json version. By default it saves a commit to git with the new version. --no-git-tag-version makes sure you don't override it.

And that is it. Now every time you make a build, the version should be generated automatically, your package.json updated and your build should have that specific version name.

App Center

Since I am using App Center to make the builds, I will tell you how you can use this in a Build machine. You only need to use a custom script.

app-center-pre-build.sh

#!/usr/bin/env sh
#Installing GitVersion
OS=$(uname -s)
if [[ $OS == *"W64"* ]]; then
    echo "Installing GitVersion with Choco"
    choco install GitVersion.Portable -y
else 
    echo "Installing GitVersion with Homebrew"
    brew install --ignore-dependencies gitversion
fi

This is needed because GitVersion is not currently a part of the build machines. Also, you need to ignore the mono dependency when installing, otherwise you get an error when brew tries to link the files.