expo.gradle

// Gradle script for detached apps.

import org.apache.tools.ant.taskdefs.condition.Os

void runBefore(String dependentTaskName, Task task) {
    Task dependentTask = tasks.findByPath(dependentTaskName);
    if (dependentTask != null) {
        dependentTask.dependsOn task
    }
}

afterEvaluate {
    def expoRoot = file("../../")
    def inputExcludes = ["android/**", "ios/**"]

    task exponentPrebuildStep(type: Exec) {
        workingDir expoRoot
        if (Os.isFamily(Os.FAMILY_WINDOWS)) {
            commandLine "cmd", "/c", ".\\android\\detach-scripts\\run-exp.bat"
        } else {
            commandLine "./android/detach-scripts/run-exp.sh", "prepare-detached-build", "--platform", "android", expoRoot
        }
    }
    runBefore("preBuild", exponentPrebuildStep)

    // Based on https://github.com/facebook/react-native/blob/master/react.gradle
    // Grab all build types and product flavors
    def buildTypes = android.buildTypes.collect { type -> type.name }
    def productFlavors = android.productFlavors.collect { flavor -> flavor.name }

    // When no product flavors defined, use empty
    if (!productFlavors) productFlavors.add("")

    productFlavors.each { productFlavorName ->
        buildTypes.each { buildTypeName ->
            // Create variant and target names
            def flavorNameCapitalized = "${productFlavorName.capitalize()}"
            def buildNameCapitalized = "${buildTypeName.capitalize()}"
            def targetName = "${flavorNameCapitalized}${buildNameCapitalized}"
            def targetPath = productFlavorName ?
                    "${productFlavorName}/${buildTypeName}" :
                    "${buildTypeName}"

            def assetsDir = file("$buildDir/intermediates/assets/${targetPath}")

            // Bundle task name for variant
            def bundleExpoAssetsTaskName = "bundle${targetName}ExpoAssets"

            def currentBundleTask = tasks.create(
                    name: bundleExpoAssetsTaskName,
                    type: Exec) {
                description = "Expo bundle assets for ${targetName}."

                // Create dirs if they are not there (e.g. the "clean" task just ran)
                doFirst {
                    assetsDir.mkdirs()
                }

                // Set up inputs and outputs so gradle can cache the result
                inputs.files fileTree(dir: expoRoot, excludes: inputExcludes)
                outputs.dir assetsDir

                // Set up the call to exp
                workingDir expoRoot

                if (Os.isFamily(Os.FAMILY_WINDOWS)) {
                    commandLine("cmd", "/c", ".\\android\\detach-scripts\\run-exp.bat", "bundle-assets", expoRoot, "--platform", "android", "--dest", assetsDir)
                } else {
                    commandLine("./android/detach-scripts/run-exp.sh", "bundle-assets", expoRoot, "--platform", "android", "--dest", assetsDir)
                }

                enabled targetName.toLowerCase().contains("release") || targetName.toLowerCase().contains("prod")
            }

            currentBundleTask.dependsOn("merge${targetName}Resources")
            currentBundleTask.dependsOn("merge${targetName}Assets")

            runBefore("process${targetName}Resources", currentBundleTask)
        }
    }
}

instructions.md

Manual standalone app update to Expo SDK 27

Make sure to update exp!

Add assetBundlePatterns to your manifest with paths to your assets folder or just the **/* wildcard:

"assetBundlePatterns": [
  "**/*"
],

iOS

In xcode, go to your project settings, build phases and create a new run script phase called Bundle Expo Assets with this as the script:

set -eo pipefail

if [ "$CONFIGURATION" == "Debug" ]; then
  echo "Skipping asset bundling in debug mode."
  exit 0
fi

pushd ${SRCROOT}/..
value=$(cat ~/.expo/PATH)
dest=$CONFIGURATION_BUILD_DIR/$UNLOCALIZED_RESOURCES_FOLDER_PATH
PATH="$PATH:$value" exp bundle-assets --platform ios --dest "$dest"
popd

Make sure your manifest contains the following keys:

• ios.publishBundlePath: "ios/<your_app_slug>/Supporting/shell-app.bundle"
• ios.publishManifestPath: "ios/<your_app_slug>/Supporting/shell-app-manifest.json"

Android

Copy the following files:

• run-exp.bat and run-exp.sh to the android/detach-scripts folder, you may also delete the other files in this directory.
• expo.gradle to the android/app folder.

You may need to grant execute permissions to run-exp.sh on unix systems (chmod +x android/detach-scripts/run-exp.sh).

In android/app/build.gradle remove the exponentPrebuildStep method and add apply from: 'expo.gradle'.

-task exponentPrebuildStep(type: Exec) {
-  workingDir '../'
-  if (System.getProperty('os.name').toLowerCase().contains('windows')) {
-    commandLine 'cmd', '/c', '.\\detach-scripts\\prepare-detached-build.bat'
-  } else {
-    commandLine './detach-scripts/prepare-detached-build.sh'
-  }
-}
-preBuild.dependsOn exponentPrebuildStep
+apply from: 'expo.gradle'

Add the following keys to your manifest:

• android.publishBundlePath: "android/app/src/main/assets/shell-app.bundle"
• android.publishManifestPath: "android/app/src/main/assets/shell-app-manifest.json"

Make sure to publish a new version first and then production builds will work offline!

run-exp.bat

SET /P STOREDPATH=<"%USERPROFILE%\.expo\PATH"
SET PATH="\"%PATH%;%STOREDPATH%\""
exp %*

run-exp.sh

#!/bin/bash

value=$(cat ~/.expo/PATH)
PATH="$PATH:$value" exp "$@"

I think this is a bit unclear. What exactly is "my manifest"?

@iuliuvisovan I think they mean app.json in the root of your project

Elsewhere, there are indications that the manifest is not the same thing as app.json. So I'm with @iuliuvisovan on this -- I don't see what or where the manifest is. I posted a question to the forum: https://forums.expo.io/t/what-where-is-the-manifest/11870

For iOS, also remember to create the file references of shell-app.bundle and shell-app-manifest.json in Xcode otherwise it won't package these files in the binary and offline support won't work. I got stuck over this for a couple of days :D