[AGP 9.1.0 Migration #9] Move aar_init_script to public AGP APIs - #193962

…Is (flutter#193962)

PR 7 (flutter#193693) merged to master as `ecd1ab06865` and PR 8 (flutter#193717) as
`4249ccbc18a`. This branch merges master at `4521d8d6634`, so the Files
tab shows only PR 9's changes.

PR 9 commits:
- `86523c549fc` Move aar_init_script to public AGP APIs
- `3edc95d1fa0` Check requested AAR variants in the module and each
plugin
- `da9646aad53` Address review: derive requested variants from
components, register AAR tasks lazily
- `94a29907065` Clarify aar_init_script comments from the adversarial
review
- `ea08280d886` Merge commit '23ddd6b74e6' into agp-aar-init-script (PR
8's head with master at `ecd1ab06865`; no conflicts, no change to PR 9's
files)
- `a17fafcc35e` Merge commit '5ba8961b517' into agp-aar-init-script
(master with PR 8 at `4249ccbc18a`; no conflicts, no change to PR 9's
files)
- `77ba449ea4a` Filter requested AAR components before adding tasks
- `adbfb9cd640` Drop the AGP version list from the duplicate-variant
comment
- `f2b7111c51e` Docs: state the AAR variant requirement in plain words
- `cd10f766b5b` Register an AAR task for every variant, publish only
requested ones
- `b9493299916` Merge commit '4521d8d6634' into agp-aar-init-script
(master, including flutter#193649; no conflicts, no change to PR 9's files)

## Description

This is PR 9 of 11 in the AGP 9.1.0 / public `gradle-api` migration
stack ([flutter#180137](flutter#180137),
[flutter#166550](flutter#166550)).

`flutter build aar` passes
`packages/flutter_tools/gradle/aar_init_script.gradle` to Gradle with
`-I`. The script read `android.libraryVariants` and AGP's internal
`publishing.singleVariants`. With AGP 9's `android.newDsl=true`,
`flutter build aar` on a module fails on `5ba8961b517` with `Can't
generate AAR on a non Android library project.` (script line 13), and
then at line 178 (`Could not get unknown property 'libraryVariants'`).
With this PR the script uses only `pluginManager.hasPlugin`,
`Publishing.singleVariant`, software `components` and `tasks.register`,
and the build succeeds with `newDsl` on and off, on AGP 9.3.1 and on
master's minimum AGP 9.1.1, and on AGP 8.11.1 when FGP's version check
is skipped.

**Breaking:** no. Builds that succeed on `5ba8961b517` succeed with the
same artifacts. Two failing cases change: a module or plugin build file
that declares `singleVariant` for only some variants builds, and a
variant mismatch between the module and a plugin fails with a Flutter
error instead of `Task with name … not found`.

**Base:** `master` at `4521d8d6634`. `aar_init_script.gradle`,
`build_aar_module_test.dart` and both docs are the same at `4521d8d6634`
and `5ba8961b517`, so the comparisons below against `5ba8961b517` hold
for `4521d8d6634`.

<details>
<summary>Agent authored details</summary>

### Changes

All in `aar_init_script.gradle` unless noted. Line numbers are at
`b9493299916`.

1. **Library check** (`:13`):
`project.pluginManager.hasPlugin("com.android.library")` replaces
`android.hasProperty("libraryVariants")`. The error text is unchanged.
2. **Publishing declarations** (`afterProject`, `:185-219`): Flutter
calls `android.publishing.singleVariant(<variant>) { withSourcesJar();
withJavadocJar() }` for each variant, one variant at a time. If the
project's build file already declared that variant, AGP throws, and
`isDuplicateSingleVariantError` (`:125-134`) matches AGP's exact
message, so the build file's declaration is kept. Its comment links the
AGP source of the message ([`AbstractPublishing.kt` at
`studio-2025.3.2`, AGP
9.1.0](https://android.googlesource.com/platform/tools/base/+/refs/tags/studio-2025.3.2/build-system/gradle-core/src/main/java/com/android/build/gradle/internal/dsl/AbstractPublishing.kt#38)).
Any other exception is rethrown (`:201-203`). The guard that read
`publishing.singleVariants` and skipped every Flutter declaration once
the build file declared any variant is deleted.
3. **No module-to-plugin `dependsOn`** (`projectsEvaluated`): the loop
over `moduleProject.android.libraryVariants` that made each module
`assembleAar<Variant>` depend on the plugin's task (with eager
`tasks.named(...).get()`) is deleted. The tool requests
`assembleAar<Variant>` without a project path (`gradle.dart`
`buildGradleAar`, `command.add(aarTask)`), and Gradle runs a task
selector that is only a task name in every project that has the task
([Gradle
docs](https://docs.gradle.org/current/userguide/command_line_interface.html#executing_tasks_in_multi_project_builds):
"You can also run a task for all subprojects using a task selector that
consists of only the task name."). Each plugin publishes from its own
task. The comment at `:247-248` says this.
4. **Tasks, publications and task name** (`configureProject` `:27-37`;
`aarTaskName` `:93-97`; `requestedAarComponents` `:99-103`): AGP adds
one software component for each `singleVariant` declaration, with the
variant's name. `registerAarTask` (`:105-110`) registers
`assembleAar<Variant>` for every component, so a misspelled `--flavor`
gets Gradle's candidate list (`Some candidates are: 'assembleAarDebug',
...`). `requestedAarComponents` returns the components whose
`assembleAar<Variant>` name is in `startParameter.taskNames`; only those
get a publication (`addAarPublication`, `:112-123`), because `publish`
publishes every publication in the project. The check uses the same
function. `aarTaskName` is the only place that builds
`assembleAar<Variant>`; its comment points to the tool's `getAarTaskFor`
(`gradle.dart`). Nothing parses a task name back into a variant. The
`component.name != "all"` filter from `5ba8961b517` is deleted (see "Why
removing the deleted code is safe").
5. **Lazy task registration** (`registerAarTask`):
`project.tasks.register` replaces `project.tasks.create(name:)`. The
configuration action only adds `finalizedBy "publish"`.
`publications.create` runs in `addAarPublication`, not in the action,
because maven-publish registers tasks for each publication and Gradle
rejects that while it realizes a task
(`DefaultTaskContainer#register(String, Class, Action) on task set
cannot be executed in the current context.`, seen when
`publications.create` was inside the action).
6. **Requested-variant check** (`checkProjectsHaveRequestedVariants`,
`:136-175`, called at `:252`): Gradle skips projects that lack the
requested task, so the script checks the module and each Android plugin.
The requested variants are the names of the components that
`requestedAarComponents` returns for those projects. A project without a
requested variant fails the build with a `GradleException` that names
the variant and the project:
- module: `Flutter can't build the AAR for variant 'debug' because
module project ':flutter' has no variant with that name. Its variants
are: demoDebug, demoProfile, demoRelease, fullDebug, fullProfile,
fullRelease. Pass the module's product flavor with --flavor, or omit
--flavor if the module has no product flavors.`
- plugin: `Flutter can't build the AAR for variant 'demoDebug' because
plugin project ':plugin_a' has no variant with that name, so the plugin
AAR that the module depends on can't be published. `flutter build aar`
requires the module and each of its Android plugins to declare the same
product flavors.`
- A requested task that matches no project's variant (for example
`--flavor foo`) is left to Gradle: `Task 'assembleAarFooDebug' not found
in root project 'android_generated' and its subprojects. Some candidates
are: 'assembleAarDebug', 'assembleAarDemoDebug',
'assembleAarFullDebug'.` That is the same error as on `5ba8961b517`. The
check's doc says so. (`3edc95d1fa0` parsed the task-name prefix and
reported a Flutter module error in this case; `da9646aad53` drops the
parsing per review.)
7. **Docs.** Both docs describe behavior only.
- `Migrating-Flutter-Gradle-Plugin-to-AGP-public-API.md`: the P8 row of
the phase table and "Features that must break" item 8 are rewritten. The
"Why" starting-state list (L38-39) is unchanged, as in other PRs of the
stack.
-
[`website-page-draft.md`](https://github.com/flutter/flutter/blob/master/docs/platforms/android/website-page-draft.md)
(publishing tracked in
[flutter#193713](flutter#193713)): the
`flutter build aar` section is rewritten. It said Flutter "detects the
overlap and reports it with an actionable error". The code keeps the
build file's declaration instead, so the docs were changed to match the
code. It says (L234-237) that when a build file declares `singleVariant`
for a variant, Flutter keeps that declaration and declares the other
variants, and (L238-241) that the module and each Android plugin need a
variant with the built name.
8. **Tests.** devicelab `build_aar_module_test` gets two final sections:
- With `android.newDsl=true` and `android.builtInKotlin=true` in
`.android/gradle.properties`, and
`android.publishing.singleVariant("release") { withSourcesJar() }` in
`.android/Flutter/build.gradle`, it runs `flutter build aar
--no-profile`. It checks that the edits survive, that release has the
AAR and sources jar and no javadoc jar, that debug has the javadoc jar,
and that the plugin AARs exist for release and debug.
- It replaces that declaration with a `demo` product flavor and checks
both errors: `flutter build aar --no-profile --no-release` fails with
the module error, and the same with `--flavor demo` fails with the
plugin error.

`da9646aad53`'s commit message says the check's doc "says when it
returns and when it throws". That doc sentence was added in
`94a29907065`.

### Bug history (moved out of the docs)

The docs describe behavior only, so the history that `3edc95d1fa0` put
in them is here:
- On `5ba8961b517`, the `afterProject` guard skipped all of Flutter's
`singleVariant` declarations for a project whose build file declared any
variant. For a module with at least one Android plugin that declared
only `release`, every `flutter build aar` failed with `Task with name
'assembleAarDebug' not found in project ':flutter'`. With this PR that
build succeeds (table 1 below).
- On `5ba8961b517`, the `dependsOn` loop failed with `Task with name
'assembleAar<Variant>' not found in project ':<plugin>'` whenever a
plugin lacked any module variant, requested or not, and nothing checked
that the module had the requested variant. With this PR only requested
variants are checked, in the module and in each plugin (table 2 below).

### Audit resolution

[PR 9 draft
audit](reidbaker-agent#9 (comment)),
and stack audit items M4 and L8:

| Item | Resolution |
| --- | --- |
| 1. Eager `.get()` and cross-project task lookup by name | The wiring
is deleted, not made lazy: it was redundant (Changes 3). No `.get()` or
`tasks.named` in the script. The check reads software components, and
`registerAarTask` uses `tasks.register`. |
| 2. Broad `catch (Exception)`; overstated `multipleVariants` warning |
Only AGP's exact duplicate message is ignored (`:130-134`); everything
else is rethrown (`:201-203`). No warning is logged, so there is no
`multipleVariants` claim. |
| 3. Ext property without `flutter.internal.` | No ext property.
`afterProject` fires once per project (instrumented: count 1 for `:`,
`:app`, `:flutter`, `:plugin_a` and the included FGP build), and a
second call would only hit ignored duplicates. The "fires more than once
in composite settings" claim is dropped. |

Why the message match and not the type: AGP reports the duplicate from
`AbstractPublishing.checkSingleVariantUniqueness` through
`SyncIssueReporterImpl`, which throws
`com.android.builder.errors.EvalIssueException` in STANDARD mode. That
class is in `com.android.tools.build:builder`, not in `gradle-api`, and
is not on the init script's classpath. `javap -v` on
`AbstractPublishing` shows the same text in AGP 8.11.1, 9.1.0 and 9.3.1.
AGP checks before it adds the component (8.11.1
`AbstractPublishing.kt:27-35`), so the build file's declaration stays.
If AGP changes the text, the exception is rethrown and the build fails
loudly; devicelab `build_aar_module_test` exercises the path on the
template AGP.

Why not declare first or query: the public `Publishing` DSL in
`gradle-api-9.1.0.jar` has only `singleVariant(String)` and
`singleVariant(String, Function1)`, and `LibraryPublishing` adds only
`multipleVariants(...)` (`javap`), so there is no public way to list
declared variants. Declaring Flutter's variants in `beforeProject` +
`pluginManager.withPlugin("com.android.library")` makes the build file
fail at its own `singleVariant("release")` line with the duplicate error
(probe).

Why not AGP types in the init script: `import
com.android.build.api.dsl.LibraryExtension` fails with `unable to
resolve class`. With `gradle-api:9.3.1` on the `initscript` classpath,
the init script gets its own copy of the class from a different
classloader, so `instanceof` is `false` and
`extensions.getByType(LibraryExtension)` throws `Extension of type
'LibraryExtension' does not exist. Currently registered extension types:
[..., LibraryExtension, ...]` (probes).

`multipleVariants`: `PublishingUtil.ensureComponentNameUniqueness`
errors only when a `multipleVariants` component name equals a
`singleVariant` name. Flutter declares the same `singleVariant`s on
`5ba8961b517` when the build file declares none, so that behavior is
unchanged. It is not tested here.

### Why removing the deleted code is safe

- `android.libraryVariants` does not exist with `newDsl=true`
(reproduced above). AGP 9.1.0 marks its class,
`com.android.build.gradle.LibraryExtension`, `@Deprecated` ("This class
is not used for the public extensions in AGP when android.newDsl=true,
which is the default in AGP 9.0, and will be removed in AGP 10.0."), and
the class is not in `gradle-api-9.1.0.jar`. `singleVariants` is an
internal property (`getSingleVariants()` on
`com.android.build.gradle.internal.dsl.AbstractPublishing`, `javap`). It
resolves from Groovy with `newDsl=true`, so it was not a failure, only
internal API.
- The `dependsOn`: with it removed, the task graph for
`assembleAarRelease` on case (a) has `:plugin_a:assembleAarRelease`,
`:plugin_a:bundleReleaseAar`,
`:plugin_a:publishReleasePublicationToMavenRepository` and
`:plugin_a:publish`. `:flutter:generatePomFileForReleasePublication`
depends on no `:plugin_a` task, and
`:flutter:publishReleasePublicationToMavenRepository` depends only on
the plugin's compile-classpath tasks, so the order between the module's
and the plugin's publishing doesn't matter. The module POM refers to the
plugin by coordinates (`plugin_a_release`). devicelab
`build_aar_module_test`, `build_android_host_app_with_module_aar` and
`android_java17_build_android_host_app_with_module_aar` pass (they check
the plugin AAR/POM and that the module POM depends on
`plugin_with_android_release`).
- The `all` filter (`component.name != "all"`, added in flutter#101891
`606e91ad63d`): AGP 7.x created an automatic multi-variant component
named `all` when a project used no publishing DSL ([`PublishingUtil.kt`
at
`studio-2021.3.1`](https://android.googlesource.com/platform/tools/base/+/refs/tags/studio-2021.3.1/build-system/gradle-core/src/main/java/com/android/build/gradle/internal/utils/PublishingUtil.kt),
`createPublishingInfoForLibrary` and `publishingFeatureOptIn`; same in
the AGP 7.3.1 jar). flutter#101891 published it separately with classifiers and
skipped it for the `_<variant>` publications; flutter#112149 (`8e30cc9c56b`)
removed that publication and kept the skip. AGP 8.0 disabled automatic
components by default ([AGP 8.0.0 release
notes](https://developer.android.com/build/releases/past-releases/agp-8-0-0-release-notes)),
and the AGP 8.11.1, 9.1.1 and 9.3.1 jars list
`android.disableAutomaticComponentCreation` as removed, with no `all`
component code. This script declares `singleVariant` for every variant,
which also turns automatic components off on AGP 7.x. A probe that
prints `project.components` after `projectsEvaluated` on all four matrix
configurations shows only per-variant names (`[debug, profile, release]`
for `:flutter`, `:app` and each plugin, `[demoDebug, …, fullRelease]`
for the flavored module, `[freeDebug, freeProfile, freeRelease]` for
`plugin_flavored`, `[debug, release]` for the root), never `all`.
- `tasks.register`: the publication is created at configuration time
only for a requested task name, as with `tasks.create`, whose
configuration closure ran immediately. Only the task object is created
lazily. Table rows below and the devicelab runs show the same artifacts.

### Removed comments, assertions and code

| Removed | Reason |
| --- | --- |
| `afterProject` comment item 2, "The project has already defined which
variants to publish…", and the `singleVariants.size()` guard it
described | The guard read internal API and skipped all of Flutter's
declarations once a build file declared any. Item 1 of that comment
became "Exit early if the project doesn't have the Android Gradle plugin
applied." |
| The `projectsEvaluated` comment "Configure the
`assembleAar<variantName>` task for each plugin's projects and make the
module's equivalent task depend on the plugin's task.", with the
`libraryVariants.all` loop, both `tasks.named(...).get()` calls, both
`assert(... != null)` and the `dependsOn` | The dependency is redundant
(see above). `tasks.named(...).get()` throws before the asserts could
fail, so they never checked anything. |
| `addAarTask` and its `variantName` local | Split into
`registerAarTask` (every component) and `addAarPublication` (requested
components). The task name comes from `aarTaskName`, which the check
also uses. |
| `addAarTask` comment "This check is required to be able to configure
the archives before `publish` runs.", with the check | The check is
`requestedAarComponents`, applied by the caller before
`addAarPublication`. Its reason is the comment on `addAarPublication`:
"`publish` publishes every publication in the project, so only requested
components get one." |
| The `component.name != "all"` filter in `configureProject`, and the
fragment "(except "all" since that is used to publish artifacts in the
new way)" from "Create a default MavenPublication for the variant" |
Nothing creates an `all` component where this script runs (see "Why
removing the deleted code is safe"). |
| From the migration doc item 8 and the website page draft: the
sentences about the deleted guard, the `Task with name … not found`
failures, and what the deleted code did and did not check | The docs
describe behavior only. The history is in "Bug history" above. |

### Behavioral and compatibility notes

Matrix projects (local scratch): (a) module + Android plugin `plugin_a`;
(b) module with flavors `demo`/`full` + `plugin_a`; (c) module +
`plugin_a` + `plugin_flavored` (flavor `free`); (d) module declaring
`singleVariant("release") { withSourcesJar() }` + `plugin_a`.

1. **A build file that declares `singleVariant` for some variants
builds.** Case (d), `flutter build aar`:

   | Script | Result |
   | --- | --- |
| `5ba8961b517` (AGP 9.3.1 `newDsl=false`) | exit 1: `Task with name
'assembleAarDebug' not found in project ':flutter'.` |
| This PR (all four configurations below) | exit 0. Release has the AAR,
POM and sources jar, and no javadoc jar (the build file's declaration).
Debug and profile have sources and javadoc jars. Plugin AAR/POM for all
three. |

2. **Variant mismatches fail with a Flutter error that names the
project.** Only requested variants are checked. The `5ba8961b517` column
is AGP 9.3.1 with `newDsl=false`.

   | Case | `5ba8961b517` | This PR (all four configurations) |
   | --- | --- | --- |
| (b) `--flavor demo` | `Task with name 'assembleAarDemoDebug' not found
in project ':plugin_a'.` | plugin error for `demoDebug` and `:plugin_a`
|
| (c) default | `Task with name 'assembleAarDebug' not found in project
':plugin_flavored'.` | plugin error for `debug` and `:plugin_flavored` |
| (b) no `--flavor`, `--no-profile --no-release` | `Task with name
'assembleAarDemoDebug' not found in project ':plugin_a'.` | module error
for `debug`, listing the module's variants |
| (c) `--flavor free`, `--no-profile --no-release` | `Task with name
'assembleAarDebug' not found in project ':plugin_flavored'.` | module
error for `freeDebug` |
| (b) `--flavor foo` | Gradle `Task 'assembleAarFooDebug' not found in
root project …` | same Gradle error |

Without the module check (`86523c549fc`), the module-error cases exit 0
with "✓ Built" and a repo that has only the plugin AAR.
3. **Path-qualified requests.** `./gradlew -I aar_init_script.gradle …
:flutter:assembleAarRelease` exits 0 and publishes nothing, on
`5ba8961b517` and on this PR: a publication is created only when
`startParameter.taskNames` contains the bare name. The tool sends only
the bare name (`gradle.dart` `command.add(aarTask)`). Not changed here.
4. **No warnings.** `flutter build aar` hides Gradle output on success
unless `-v` (`ProcessUtils.run` buffers it; `gradle.dart` prints it only
on failure, and verified with a `logger.error` probe). Keeping a build
file's declaration needs no action, so nothing is logged. Errors are
shown.
5. **Configuration cache:** with `org.gradle.configuration-cache=true`
in case (a)'s `.android/gradle.properties` (AGP 9.3.1 / Gradle 9.5.0),
`flutter build aar` reports the same single problem with the
`5ba8961b517` script and with this PR: ``Task
`:flutter:compileFlutterBuildDebug` of type
`com.flutter.gradle.tasks.FlutterTask`: invocation of 'Task.project' at
execution time is unsupported with the configuration cache.`` None comes
from the init script.
6. `newDsl=true` with `builtInKotlin=false` fails before the script with
any Kotlin plugin (`The 'org.jetbrains.kotlin.android' plugin is not
compatible with AGP's 9.0 new DSL`). The devicelab section and matrix
set `builtInKotlin=true`.
7. Related open work: no overlap with
[flutter#191681](flutter#191681)
(`gradle.dart`, `gradle_errors.dart` and tests). No open PR touches
`aar_init_script.gradle`.

### Follow-up candidates (pre-existing, not changed here)

- `allprojects { apply plugin: "maven-publish" }` applies maven-publish
to every project, including ones that never publish.
- The `afterProject` and `projectsEvaluated` hooks reach across
projects, which Gradle Isolated Projects does not allow.
- The `-SNAPSHOT` rewrite of `project.version` in `configureProject`.
- The `engine.realm` and `engine.stamp` file reads at configuration time
in `configureProject`.
- The `is-plugin` branch of `projectsEvaluated` looks unreachable from
the tool.
- The configuration cache problem in FGP `FlutterTask` (note 5).
- `newDsl=true` with KGP (`builtInKotlin=false`), for PR 10.
- Mapping between flavored module variants and plugin variants (for
example, plugin `release` for module `demoRelease`).
- `singleVariant` is declared on the root project and `:app`, which
never publish.
- Gradle output is hidden on success, so nothing the script logs at info
or warn level reaches the user without `-v`.

### Integration test coverage of the changed paths

Searched `dev/devicelab/bin/tasks` and
`packages/flutter_tools/test/integration.shard` for `build aar` and
`assembleAar`.

| Path | Tests |
| --- | --- |
| Library check, publishing declarations, lazy task registration, plugin
publishing without `dependsOn` (`newDsl=false`) | devicelab
`build_aar_module_test`, `build_android_host_app_with_module_aar`,
`android_java17_build_android_host_app_with_module_aar`;
`android_obfuscate_test` |
| `newDsl=true`, a build file's `singleVariant` declaration kept |
devicelab `build_aar_module_test`, `newDsl=true` section |
| Module and plugin variant mismatch errors | devicelab
`build_aar_module_test`, product flavor section |
| AGP 9.1.1 and 8.11.1; a variant that no project has | Manual matrix
only |

`Linux build_aar_module_test` runs in presubmit for this PR: in
`.ci.yaml` its `runIf` includes `dev/**` and
`packages/flutter_tools/**`, and it sets neither `presubmit: false` nor
`bringup`. It also ran locally on the head (below) with `cd
dev/devicelab && ../../bin/dart bin/test_runner.dart test -t
build_aar_module_test --exit`.

### Tests run locally (macOS, JDK 17)

On the head (`b9493299916`; master merged at `4521d8d6634`):

- `gradle test --rerun-tasks` in `packages/flutter_tools/gradle`, with
the engine's `third_party/gradle` binary that the README names: 33
suites, 277 tests, 0 failures.
- `dart format` and `dart analyze --fatal-infos` on
`build_aar_module_test.dart`: clean (unchanged since `3edc95d1fa0`).
- Tool tests: `test/commands.shard/hermetic/build_aar_test.dart`,
`test/commands.shard/permeable/build_aar_test.dart` and
`test/general.shard/android/android_gradle_builder_test.dart`: 56 tests,
all pass.
- `test/integration.shard/android_obfuscate_test.dart`: 2 tests pass.
- devicelab via `bin/test_runner.dart test --exit`, one at a time:
`build_aar_module_test` (including both added sections),
`build_android_host_app_with_module_aar`,
`android_java17_build_android_host_app_with_module_aar`,
`build_android_host_app_with_module_source`,
`module_host_with_custom_build_test`, all `success`.
- The configuration cache comparison (note 5).

Manual matrix on `b9493299916`, four configurations:
- **9.3.1 off:** AGP 9.3.1 / Gradle 9.5.0, `newDsl=false`,
`builtInKotlin=false`.
- **9.3.1 on:** AGP 9.3.1 / Gradle 9.5.0, `newDsl=true`,
`builtInKotlin=true`.
- **9.1.1 on:** AGP 9.1.1 / Gradle 9.3.1 (FGP's minimums on master since
flutter#193813), `newDsl=true`, `builtInKotlin=true`.
- **8.11.1:** AGP 8.11.1 / Gradle 8.14.3, `newDsl=false`, with
`skipDependencyChecks=true` in `.android/gradle.properties`. Without it,
FGP stops before the init script runs: `Your project's Gradle version
(8.14.3) is lower than Flutter's minimum supported version of 9.3.1.`

| Case | 9.3.1 off | 9.3.1 on | 9.1.1 on | 8.11.1 |
| --- | --- | --- | --- | --- |
| (a) | exit 0, AAR, POM, sources and javadoc jars for
`flutter_{debug,profile,release}` and `plugin_a_{debug,profile,release}`
| same | same | same |
| (b) `--flavor demo` | exit 1, plugin error | same | same | same |
| (b) no `--flavor` | exit 1, module error | same | same | same |
| (b) `--flavor foo` | exit 1, Gradle `Task 'assembleAarFooDebug' not
found in root project` | same | same | same |
| (c) | exit 1, plugin error | same | same | same |
| (c) `--flavor free` | exit 1, module error | same | same | same |
| (d) | exit 0, as (a), except module release has the sources jar and no
javadoc jar | same | same | same |

Case (a)'s `flutter_release-1.0.pom` depends on
`dev.pr9.plugin_a:plugin_a_release:1.0` (checked on `b9493299916`, AGP
9.1.1).

Negative control, the master script (same at `5ba8961b517` and
`4521d8d6634`), on `b9493299916`: with `newDsl=true` (AGP 9.3.1 and AGP
9.1.1), (a)-(d) all fail with `Can't generate AAR on a non Android
library project.`; with `newDsl=false` on AGP 9.3.1, (a) passes and
(b)-(d) fail with Gradle's `Task with name 'assembleAar<V>' not found in
project ':<p>'.` On `a17fafcc35e`, with only line 13 changed to
`hasPlugin`, `newDsl=true` fails at line 178 with `Could not get unknown
property 'libraryVariants' for object of type
com.android.build.gradle.internal.dsl.LibraryExtensionImpl$AgpDecorated.`
devicelab `build_aar_module_test` with that script fails at the
`newDsl=true` section with the same error.

</details>

---

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [AI contribution guidelines] and understand my
responsibilities, or I am not using AI tools.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant in-code documentation (doc comments with
`///`).
- [x] If this PR introduces a new feature or capability, I created and
linked a website documentation issue or PR in [flutter/website] (or
verified none is needed).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [x] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.

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…APIs (#195640)

This pull request is created by [automatic cherry pick workflow](https://github.com/flutter/flutter/blob/main/docs/releases/Flutter-Cherrypick-Process.md#automatically-creates-a-cherry-pick-request)
Please fill in the form below, and a flutter domain expert will evaluate this cherry pick request.

### Issue Link:
What is the link to the issue this cherry-pick is addressing?

#180137

### Impact Description:
What is the impact (ex. visual jank on Samsung phones, app crash, cannot ship an iOS app)?
Does it impact development (ex. flutter doctor crashes when Android Studio is installed),
or the shipping of production apps (the app crashes on launch).
This information is for domain experts and release engineers to understand the consequences of saying yes or no to the cherry pick.

Cherry-pick of #193962 (also tracks #166550).

On Flutter 3.50 beta (`flutter-3.50-candidate.0`), PRs #1–#8 of the Android Gradle Plugin (AGP) 9 public-API migration have already landed, allowing standard Android apps and source-included add-to-app modules to opt into AGP 9's new DSL (`android.newDsl=true` and `android.builtInKotlin=true`). However, `flutter build aar` passes `packages/flutter_tools/gradle/aar_init_script.gradle` to Gradle, which still accesses `android.libraryVariants` and AGP's internal `publishing.singleVariants`. Because AGP 9 removes `BaseExtension` / `libraryVariants` when `android.newDsl=true`, `flutter build aar` fails 100% of the time on Android modules opting into `android.newDsl=true` (`Can't generate AAR on a non Android library project.` / `Could not get unknown property 'libraryVariants'`). Without this cherry-pick, add-to-app teams packaging Flutter modules as AARs cannot adopt AGP 9's new DSL on Flutter 3.50.

### Changelog Description:
Explain this cherry pick:
* In one line that is accessible to most Flutter developers.
* That describes the state prior to the fix.
* That includes which platforms are impacted.
See [best practices](https://github.com/flutter/flutter/blob/main/docs/releases/Hotfix-Documentation-Best-Practices.md) for examples.

[flutter/180137](#180137): When running `flutter build aar` on Android with `android.newDsl=true` (AGP 9), the build fails because `aar_init_script.gradle` references legacy AGP variant APIs.

### Workaround:
Is there a workaround for this issue?

Keep `android.newDsl=false` in `.android/gradle.properties` when running `flutter build aar`, which prevents Flutter module projects from adopting AGP 9's new DSL.

### Risk:
What is the risk level of this cherry-pick?

### Test Coverage:
Are you confident that your fix is well-tested by automated tests?

### Validation Steps:
What are the steps to validate that this fix works?

1. Create a Flutter module (`flutter create --template=module my_module`).
2. Opt `.android` into AGP 9's new DSL by setting `android.builtInKotlin=true` and `android.newDsl=true` in `.android/gradle.properties` (and ensuring `kotlin-android` is not applied).
3. Run `flutter build aar` inside `my_module` and verify that debug, profile, and release AAR artifacts and Maven POMs are generated in `build/host/outputs/repo` without `libraryVariants` or `Can't generate AAR on a non Android library project.` errors (covered in CI by `dev/devicelab/bin/tasks/build_aar_module_test.dart`).