See related issue: hapifhir/hapi-fhir#3690

Under this issue, let's create a PR to diverge the Engine and SDC API level from workflow API level.

A few more learnings from this process: MinSDK 26 is the sweet spot. It offers enough runtime API to support all of the test cases in this project while removing desugaring which doubles the compilation speed. It's a win-win. We could go down to 24 with desugaring in the engine + SDC and keep the workflow on 26. I don't think this project works with <= 23 anymore (we haven't been testing for such low SDKs).

Issues that can be resolved with current Desugaring lib

Uses of java.time by this project, by HAPI 6, and by Caffeine require MinSDK 26 or Desugaring w/ 24, which provides a workable subset of java.time and a fixed ConcurrentHashMap for caching solutions.

The version of Kotlin's Stdlib must match the desugaring + minSDK strategy as well. This link provides good information to choose correctly when migrating.

Issues that can be resolved with newer Desugaring

The version of the desugaring library (com.android.tools:desugar_jdk_libs) indicates what API methods will be available. The version we use is quite old 1.1.5, but updating to 2.0.0 while on min SDK 24 triggers RuntimeExceptions on android.content.pm.PackageParser$PackageParserException at PackageParser.java for the data capture module. We can't update this lib until we solve this issue.

Issues that cannot be resolved with Desugaring but can be fixed by minSDK 26

CQLEngine 2.0, HAPI-fhir-base 5 and some versions of Jackson (2.13.2) make use of java.lang.reflect.Method.getParameterCount() which is not available before 26. We have overridden those Jackson versions with corrected versions, but it might come back. For example, the use of hapi-fhir-base's PropertyModifyingHelper will crash the app on runtime.

Right now this means that the workflow module absolutely requires min SDK 26.

java.nio.file, which is now frequently used by HAPI, is not available before 26. This doesn't break our test cases yet, but with NPM Package Manager (@ktarasenko) being based on filesystem, we can expect heavy use of this new API in the near future.

Issues that cannot be resolved by us.

HAPI's dependency Caffeine 3.0 is not compatible with Android due to the widespread use of JEP-264: Platform Logging API's System.getLogger to redirect logs to slf4. System.getLogger is not provided by either desugaring or newer versions of the SDK. For now, we have to force Caffeine ~2.9

• The solution is to: Extracts Caching Libraries into Service Loaders (Caffeine -> Java, Guava -> Android) hapifhir/hapi-fhir#3977

CQLTranslator is graciously helping us by forcing the use of Woodstox for now. The default XmlFactory provided by Jackson calls a Streaming API for XML (StAX) javax.xml.stream.XMLInputFactory.newFactory function that does not exist on Android: javax.xml.stream.XMLInputFactory.newFactory

• Discussion here: Forcing Woodstox on all Jackson modules?  cqframework/clinical_quality_language#768

Uses of java.util.Optional.isEmpty() in any dependent library will only work on SDK 33+

Uses of java.util.List.toArray(java.util.function.IntFunction) will not work on any Android version.

thanks for the excellent write-up vitor. i've created #1628.

After some deeper analysis, I can say that the HAPI dependencies we use (base + structures + validators + resources) are fully compliant with SDK 26

They are not compliant with 24, even with desugaring on.

Here are the problems:

[ERROR] ~/hapi-fhir-base/../../BundleUtil.java:299: Undefined reference: String String.join(CharSequence, Iterable)
[ERROR] ~/hapi-fhir-base/../../TimeoutManager.java: Undefined reference: java.time.Duration
[ERROR] ~/hapi-fhir-base/../../TimeoutManager.java: Undefined reference: java.time.Duration
[ERROR] ~/hapi-fhir-base/../../TimeoutManager.java:53: Undefined reference: long java.time.Duration.toMillis()
[ERROR] ~/hapi-fhir-base/../../TimeoutManager.java:58: Undefined reference: long java.time.Duration.toMillis()
[ERROR] ~/hapi-fhir-base/../../TimeoutManager.java:72: Undefined reference: long java.time.Duration.toMillis()
[ERROR] ~/hapi-fhir-base/../../PropertyModifyingHelper.java:77: Undefined reference: int java.lang.reflect.Method.getParameterCount()
[ERROR] ~/hapi-fhir-base/../../DateUtils.java:109: Undefined reference: ThreadLocal ThreadLocal.withInitial(java.util.function.Supplier)
[ERROR] ~/hapi-fhir-base/../../RequestPartitionId.java: Undefined reference: java.time.LocalDate
[ERROR] ~/hapi-fhir-base/../../RequestPartitionId.java:102: Undefined reference: java.time.LocalDate

PRs to assert compliance to 26 were sent to:

• Android compatibility checks hapifhir/hapi-fhir#4070
• Formalizes compliance with Android 8, SDK 26 (2017+) cqframework/clinical_quality_language#810
• Formalizes compliance with Android 8, SDK 26 (2017+)  cqframework/cql-engine#613
• Formalizes compliance with Android 8, SDK 26 (2017+) cqframework/clinical-reasoning#157

@vitorpamplona , can this issue be closed since the related PR is already merged?
CC: @jingtang10

Yep. This was solved

@Tarun-Bhardwaj I would turn this into a schedule of MinSDK changes. The issues discussed here go away with minSDK 26 (we are sticking to 24 right now). At some point in the future, the engine will have to move to 26. The earliest we can commit to a date, the better the developer experience using the SDK.