[jnigen] Remove the need to run flutter build apk by liamappelbe · Pull Request #3303 · dart-lang/native

liamappelbe · 2026-04-13T23:58:47Z

This PR removes the need to run flutter build apk.

The only important changes are in pkgs/jnigen/lib/src/tools/android_sdk_tools.dart, in the gradle stubs.

JNIgen gathers dependencies by injecting a temporary stub into the build.gradle file. The goal of the stub is to find all the relevant files, and print their paths stdout. Gradle is then run in a subprocess and the paths are read from its stdout. There are 4 stubs, because we need to support loading JARs (classpath stub) vs loading source files, and we need to support both Groovy and Kotlin build.gradle files.

The stubs have been completely rewritten. All four now use the same 3 step process:

Tell gradle that all the subprojects are dependencies of this project. This is necessary for multi project setups like when you have a Flutter plugin and its example app.
Get all the JARs from all the dependencies.
Extract the paths we care about from the JARs.

Steps 1 and 2 happen at config time, and step 3 happens at doLast time. Unfortunately this leads to some code duplication, because we need very similar looking queries to find all the JARs in steps 2 and 3.

The classpath stub now has to explicitly extract all the JAR files that are stored in AARs. That used to happen automatically during flutter build apk.

The old classpath stubs made sure to list the android.getBootClasspath first, so that JNIgen would see them first. That way, any duplicates of the core libraries would be ignored. This is particularly important for dealing with the Jetifier on Android, which produces a bunch of stub classes for core libraries. The new classpath stubs make sure to maintain the same ordering.

Examples

I added example/maven_lib and example/maven_lib_groovy to test the new stubs, because I found the existing examples were a bit too simple. They're identical except that they use Kotlin and Groovy respectively in their build.gradle files

They're plugins that depend on GSON and OkHttp as maven dependencies (rather than checking in their source code into third_party). The plugin depends on GSON, and the plugin's example app depends on OkHttp, but the bindings for both exist in the plugin. It's a weird dependency layout designed to stress test the stubs.

gradlew files

There's one other thing that flutter build apk does that we didn't anticipate: create the gradelw files if they're missing. The default Flutter .gitignore policy is to exclude these from the repo, though it's also valid to check these files into your github repo (in fact that's the recommended policy according to the gradle docs).

We work around this by automatically running flutter build apk --config-only when JNIgen is run in a flutter app. This is a lightweight command to run, and creates the gradle wrappers if they're missing. It also implicitly runs flutter pub get, which is handy.

To test the checked-in workflow, I'm also checking in the gradle wrappers for the maven_libs_groovy example.

Fixes #628
Fixes #1661
Fixes #1660
Related #1972
Related #576

github-actions · 2026-04-14T00:01:29Z

PR Health

Changelog Entry ✔️

Package	Changed Files

Changes to files need to be accounted for in their respective changelogs.

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Breaking changes ✔️

Package	Change	Current Version	New Version	Needed Version	Looking good?
jni_flutter	None	1.0.1	1.0.1	1.0.1	✔️

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API leaks ✔️

The following packages contain symbols visible in the public API, but not exported by the library. Export these symbols or remove them from your publicly visible API.

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dcharkes

It's also valid to check these files into your github repo. In fact that's the recommended policy according to the gradle docs. It has been suggested that Flutter should change this default gitignore, but there's been some push back. The push back in Flutter seems fairly mild to me, so if this becomes an issue for many users we can probably file an issue about it.

@reidbaker What are your thoughts on checking in these files in Flutter plugins that depend on JNIgen so that JNIgen can run without having to run flutter build apk?

dcharkes · 2026-04-15T07:31:00Z

+# Allow Gradle wrapper
+!gradlew
+!gradlew.bat
+!gradle-wrapper.jar


These are 52kb jars? Why do we need to commit them?

This is a part of bootstrapping Gradle and making sure the intended version of gradle is the one that is used to build the underlying project.

Another option would be to do flutter build apk --config-only in the workflows. This creates the gradlew files without actually doing a build.

As discussed offline:

We can check in one project with all the generated files.

And for the other projects we can detect it's a flutter project and run flutter build apk --config-only inside JNIgen.

For a future where we have hooks/generate.dart, Flutter should make sure flutter build apk --config-only is run before the generate hook so that automatic detection would become a noop.

dcharkes · 2026-04-15T07:33:41Z

@@ -0,0 +1 @@
+TODO: Add your license here.


Do we need to have the Dart license for our example projecs?

The other examples don't have a LICENSE file. Deleted.

dcharkes · 2026-04-20T15:56:39Z

+      throw e
+    }
+  }
+  System.err.println("If you are seeing this error in `flutter build` output, it is likely that JNIgen left some stubs in the build.gradle file. Please restore that file from your version control system or manually remove the stub functions named getReleaseCompileClasspath and / or getSources.")


Would it be useful to have a docs markdown file where we can point from the error message so that we can add docs there. Or even a GitHub issue?

🤷 Not sure what needs to be expanded into a doc in this error message. Is there more we need to say here?

dcharkes · 2026-04-20T15:57:11Z

+
+  static void _runFlutterConfigOnly(String androidProject) {
+    // Only run if it looks like a flutter project.
+    if (!File(join(androidProject, 'pubspec.yaml')).existsSync()) {


Haha, best heuristic ever 😆

dcharkes · 2026-04-20T15:58:25Z

-                jni$_.JMethodIDPtr,
-                jni$_.VarArgs<(jni$_.Pointer<jni$_.Void>,)>,
-              )>>('globalEnv_CallObjectMethod')
+              jni$_.NativeFunction<


did the formatter change? what version of the formatter are we using?

Some combination of flutter create and gemini CLI initially created the examples with the SDK version set to the most recent Dart version. This caused problems on CI, so I had to change it to match the bounds of the other examples, which caused formatting changes.

goderbauer

Maybe also update the PR description for future archeologists (i.e. the section about "gradlew files" and how we now attempt to autogenerate them)?

goderbauer · 2026-04-21T09:57:30Z

+
+  static void _runFlutterConfigOnly(String androidProject) {
+    // Only run if it looks like a flutter project.
+    if (!File(join(androidProject, 'pubspec.yaml')).existsSync()) {


Why's the presence of a pubspec.yaml enough to assume a Flutter project? How is it garanteed that it isn't a standalone dart project?

This whole flow is gated by Config.androidSdkConfig being non-null, so it should only be run for Android projects. Though I guess by that argument we probably don't need the pubspec check at all. Probably should just check the flutter: key exists.

goderbauer

LGTM 🚀

WIP [jnigen] Remove the need to run flutter build apk

712ffc0

github-actions Bot added type-infra A repository infrastructure change or enhancement package:jnigen labels Apr 13, 2026

Check in gradelw files

5447cd3

github-actions Bot added package:jni package:jni_flutter labels Apr 14, 2026

liamappelbe added 15 commits April 14, 2026 13:33

Fix notification plugin dep issue

b20a630

more deps

51aa2a7

wip

2814eff

remove unnecessary deps changes

5ed7db3

Fix groovy syntax

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wip

23073b9

wip

f24b03a

cleaning

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cleaning

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cleanup

dcfc9cd

examples

15fa45c

example test

72c90ac

Update example readmes

5dcd00a

fmt

4fcbf5d

Update more readmes

3d606d3

liamappelbe changed the title ~~WIP [jnigen] Remove the need to run flutter build apk~~ [jnigen] Remove the need to run flutter build apk Apr 15, 2026

liamappelbe added 2 commits April 15, 2026 16:30

debugging fmt errors

e33d436

fmt

15e5e50

liamappelbe marked this pull request as ready for review April 15, 2026 06:36

liamappelbe requested review from dcharkes and jwill April 15, 2026 06:36

dcharkes reviewed Apr 15, 2026

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reviewer comments

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goderbauer reviewed Apr 16, 2026

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Comment thread pkgs/jnigen/example/maven_libs/CHANGELOG.md Outdated

Comment thread pkgs/jnigen/example/maven_libs_groovy/CHANGELOG.md Outdated

Comment thread pkgs/jnigen/example/maven_libs/example/analysis_options.yaml Outdated

liamappelbe added 4 commits April 17, 2026 13:54

Delete useless files and auto-run flutter build apk --config-only

fda9f6c

remove gradlew files

896eefe

Only allow gradlew files in maven_libs_groovy

8f64536

revert extra deletions

4d7a08e

github-actions Bot removed the package:jni label Apr 17, 2026

liamappelbe added 4 commits April 17, 2026 14:45

Regen bindings

b02244e

increase maven example timeout

8ec48d7

fix windows ci

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increase timeouts

9f432a3

liamappelbe requested review from dcharkes and goderbauer April 20, 2026 03:45

dcharkes approved these changes Apr 20, 2026

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Remove JNIgen stubs from gradle file

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goderbauer reviewed Apr 21, 2026

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more comments

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goderbauer approved these changes Apr 22, 2026

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liamappelbe merged commit 27890da into main Apr 22, 2026
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liamappelbe deleted the jnigen_no_build branch April 22, 2026 08:11

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liamappelbe commented Apr 13, 2026 •

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