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Fix #3622, #4238, #3861, part of #4044: Fix state player deadlock by migrating progress controllers over to a command-queue structure #4239

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Mar 27, 2022

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@BenHenning BenHenning commented Mar 10, 2022

Explanation

Fix #3622
Fix #4238
Fix #3861
Fix part of #4044 (see below for how this relates to the broader math expressions project)

This PR fixes a deadlock that's possible in both QuestionAssessmentProgressController and ExplorationProgressController wherein the internal locks used to synchronize session state can conflate with the locks of the controllers' HintHandlers (which calls back into the controller within the lock). While this seems really difficult to hit when playing a training session or exploration, StateFragmentTest seems to very consistently hit the deadlock after only 10-15 tests (so it essentially can't be run without the fixes introduced here).

While I could've tried rearranging the locks to be more cooperative, it's actually difficult to guarantee that deadlocks won't happen without rebuilding the internal locking mechanism for controller data. I chose the latter by introducing a command queue-esque pattern using a Kotlin actor with StateFlows for pushing state back to callers (see https://kotlinlang.org/docs/shared-mutable-state-and-concurrency.html; actors are a powerful way to leverage the lightweight nature of coroutines to manage cross-thread state machines). To simplify the implementation, this PR also introduces conversion methods from StateFlows to DataProviders (I could see us leveraging these flows more in the future, maybe as a long-term replacement to DataProviders with some refinement).

One side effect of using a command queue to manage what is effectively a session state is that state can now fairly easily leak between sessions. Efforts have been taken to minimize the chance of this happening (mainly ignoring events that arrive from a previously ended session), but a better long-term solution would be to create new session controllers for each session (which should be something possible with custom scopes once we integrate Dagger Hilt in #1720).

Due to a general push toward using DataProviders much more heavily in these controllers rather than LiveData, AsyncResult needed to be refactored in order for some of the internal transformed chains in the controllers to work correctly (which is where #4237 comes in).

This also permanently fixes #3861 and other potential errors that could happen by ensuring that the provider state can continue even if internal errors are encountered rather than entering a permanently broken state (#4230 mitigates the immediate repro steps from the bug by fixing the underlying issue that caused the exception, whereas this PR focuses on preventing those scenarios from causing the bug in question).

Some explanations for the threading approach

I was originally going to make hint handler also a command queue, but it became a bit complicated. To keep things simpler, I removed the threading restricting on it so that it can only be accessed on a single thread (similarly to the internal progress objects used by both controllers) which helps avoid needing a lock without worrying about data races. Note that this command queue style implementation of HintHandler is available to view in the past commits in this PR if it's interesting for future development (since it's a simpler command queue than the ones used by the controllers due to having an inherently simpler internal state machine).

This PR demonstrates a general tendency to move the app toward a 'notify-and-pull' model (e.g. DataProviders) vs. a push-subscribe pattern. The former is easier to synchronize, parallelize, ensure lifecycle safety, and is often more performant since operations only need to execute when their results are needed.

Note that both controllers' internal computation behaviors are completely different with this new approach. Previously, the internal progress state machine would only be fully processed when the current ephemeral state/question was retrieved from the UI layer (i.e. lazily), but now it's computed shortly after the change (i.e. eagerly) since that works a bit better with the Flows being used for internal cross-thread communication. This technically means the controllers are slightly less efficient since execution may happen in cases when the state/question is no longer being viewed by the user, but it should realistically make a small difference since we have to thread hop for the command queue, anyway, and computing the ephemeral state/question should be cheap. This has the benefit of a potentially snappier load experience in the frontend, though, since the ephemeral state/question will be available sooner.

All operations in the controllers now execute their operations regardless of whether they're observed (which should better match callers' expectations).

Note that the internal state machine complexity can probably be drastically simplified now that the command queue can also act as a state machine, but I didn't want to risk regressions by removing it (I was trying to keep the logical flow as similar as possible to the existing behavior).

Updates to dependencies

The coroutines core dependency needed to be updated since the older version didn't include StateFlow which was necessary for providing a sync-back mechanism for the controller command queues.

Stability checks

I verified that both QuestionPlayerActivity and StateFragmentTest pass on Espresso (where the latter deadlocked prior to this PR); see the screenshots below. Further, I tested ExplorationProgressControllerTest and QuestionAssessmentProgressControllerTest 100x times to verify both are not flaky (since some flakes were discovered during development). Both test suites passed all 100 runs.

Bazel app module tests

This PR introduces support for dedicated app module tests in Bazel (rather than bundling them as part of the broader list of app module tests). This required a few changes in .bzl and .bazel files, but the change is otherwise straightforward and extremely beneficial for team members that rely on the Android Studio with Bazel plugin for regular development.

Miscellaneous

I tried introducing a Bazel emulator test while developing this (as part of #59) but it ran into a desugar issue with Mockito and Robolectric (due to them both being pulled into the test binary that's being built to send to the device) which AGP apparently works around. See bazelbuild/bazel#13684 for a Bazel issue tracking the same issue.

This fixes #3622 since it eliminates the lock entirely in favor of using actors for safe cross-thread communication. The MediatorLiveData specific part of this issue's TODO comment isn't relevant anymore, either, since we replaced MediatorLiveData with a custom notifying LiveData within DataProviders a while back.

This fixes #4238 fully by ensuring any exceptions caused within the state flow of an exploration or questions session are captured and logged, but don't actually break the internal state machine of the session. This issue was discovered during the development of #2173 due to an exception being thrown in the classifier. While that issue was fixed, a test couldn't actually be added for the #4238 fix since it's difficult to intentionally trigger exceptions during answer classification.

A note on checkpoints in ExplorationProgressController

The checkpointing behavior in ExplorationProgressController became more complex as a result of these changes. In particular, checkpointing behaves as follows:

  • Something changes in the play session
  • A checkpoint recomputation is requested (which results in a new checkpoint being computed and then saved to disk)
  • The checkpoint is 'processed' by updating the play state of the exploration (i.e. in StoryProgressController)
  • The ephemeral state is recomputed since it contains the checkpoint and the checkpoint has changed

Each of these more or less require a command queue "hop" which means other operations can occur between them. As a result, #3467 can still occur since an exploration can be finished before the process happens (though the behavior has changed: the progress simply won't be processed which means an exploration might not be indicated as played, but the checkpointing should almost always be saved before the exploration session end is processed). Fixing this isn't straightforward since the exploration's play state can't be changed until the checkpoint is confirmed as saved which either requires updating StoryProgressController to also account for the presence of checkpoints, or to use more flows internally to combine the save-and-process operation into one in a way that doesn't lock up ExplorationProgressController (I'm currently not exactly sure how one would do this, but I haven't thought about it in depth yet).

Essential Checklist

  • The PR title and explanation each start with "Fix #bugnum: " (If this PR fixes part of an issue, prefix the title with "Fix part of #bugnum: ...".)
  • Any changes to scripts/assets files have their rationale included in the PR explanation.
  • The PR follows the style guide.
  • The PR does not contain any unnecessary code changes from Android Studio (reference).
  • The PR is made from a branch that's not called "develop" and is up-to-date with "develop".
  • The PR is assigned to the appropriate reviewers (reference).

For UI-specific PRs only

This PR does not intentionally change and user-perceivable behaviors in the questions or state players except potentially fixing deadlocks/ANRs that could occur while playing. There could be regressions in the players, and they may potentially be more performant after this change, but neither can easily be demonstrated via videos or screenshots. There are no accessibility behavior changes to demonstrate, either.

However, two key tests have been run and verified as passing on Espresso to demonstrate that the deadlock has been fixed. Specifically:

QuestionPlayerActivityTest StateFragmentTest
deadlock_fix_pr_question_player_activity_test_passing deadlock_fix_pr_state_fragment_test_passing

…isons-protos' into add-support-for-math-expressions-pt5-polynomial-protos
… into add-support-for-math-expressions-pt6-tokenizer

Conflicts:
	scripts/assets/test_file_exemptions.textproto
…d-support-for-math-expressions-pt7-math-expression-parser
…rser' into add-support-for-math-expressions-pt8-latex-conversion-and-eval
…nd-eval' into add-support-for-math-expressions-pt9-commutative-comparisons
This adjusts for the removal of ComparableOperationList (i.e. no wrapper
proto).
This includes fixes to the converter itself as it wasn't distributing
both product inversions and negation correctly in several cases. Tests
should now be covering these cases.
Still needs to be cleaned up, but after converter refactoring attempts.
…isons' into add-support-for-math-expressions-pt10-polynomials

Conflicts:
	utility/src/main/java/org/oppia/android/util/math/MathExpressionExtensions.kt
	utility/src/main/java/org/oppia/android/util/math/PolynomialExtensions.kt
	utility/src/main/java/org/oppia/android/util/math/RealExtensions.kt
Also, clean up polynomial sorting.
… add-support-for-math-expressions-pt11-numeric-expression-input-classifiers

Conflicts:
	utility/src/main/java/org/oppia/android/util/math/MathExpressionExtensions.kt
	utility/src/main/java/org/oppia/android/util/math/PolynomialExtensions.kt
	utility/src/main/java/org/oppia/android/util/math/RealExtensions.kt
Also, mark methods/classes that need tests.
… into add-support-for-math-expressions-pt6-tokenizer
This adds explicit platform selection support rather than it being
automatic based on deps. While less flexible for shared tests, this
offers better control for tests that don't want to to use Robolectric
for local tests.

This also adds a JUnit-only test runner, and updates MathTokenizerTest
to use it (which led to an almost 40x decrease in runtime).
Also, fix name for the AndroidJUnit4 runner.
…nd-eval' into add-support-for-math-expressions-pt9-commutative-comparisons
…isons' into add-support-for-math-expressions-pt10-polynomials
… add-support-for-math-expressions-pt11-numeric-expression-input-classifiers
…n-input-classifiers' into add-support-for-math-expressions-pt12-algebraic-expression-input-classifiers
…ion-input-classifiers' into add-support-for-math-expressions-pt13-math-equation-input-classifiers
…ut-classifiers' into add-support-for-math-expressions-pt14-enable-math-classifiers
…ifiers' into add-support-for-math-expressions-pt15-math-expression-accessibility-string
…ccessibility-string' into add-support-for-math-expressions-pt16-latex-rendering
…port-for-math-expressions-pt16-latex-rendering
Base automatically changed from refactor-async-result to develop March 27, 2022 05:43
@BenHenning BenHenning requested a review from rt4914 as a code owner March 27, 2022 05:43
BenHenning added a commit that referenced this pull request Mar 27, 2022
…ss (#4237)

## Explanation
Fix #3813
Fix #92
Fix part of #4044 (see below for how this relates to the broader math expressions project)

This PR refactors ``AsyncResult`` to be a sealed class rather than using enums which has a distinct advantage: the strong typing guarantees from a sealed class ensure the presence of certain data is guaranteed (such as the ``Throwable`` from the failing ``AsyncResult``). However, this refactor is very far-reaching since essentially every usage of ``AsyncResult`` needed to be updated (though not necessarily just references).

### High-level ``AsyncResult`` pattern changes
Here are comparisons in how the common operations have changed:

Before:
```kotlin
val result: AsyncResult<String> = fetchOrReceiveSomeResult()

// Construction.
val pending = AsyncResult.pending<String>()
val failure = AsyncResult.failure<String>(IllegalStateException("Failure reason"))
val success = AsyncResult.success("success value")

// Check type.
val isPending = result.isPending()
val isFailure = result.isFailure()
val isSuccess = result.isSuccess()
val isCompleted = result.isCompleted()

// Retrieve success values.
val successValue1 = result.getOrDefault("default string")
val successValue2 = result.getOrThrow()

// Retrieve failure reason.
val failureReason = result.getErrorOrNull()

// Generic type check.
when (result) {
  // We typically ignore the pending case.
  result.isFailure() -> { /* Do something with result.getErrorOrNull() */ }
  result.isSuccess() -> { /* Do something with result.getOrDefault() or result.getOrThrow() */ }
  // The 'else' case is possible, and often not implemented.
}
```

After:
```kotlin
val result: AsyncResult<String> = fetchOrReceiveSomeResult()

// Construction.
val pending = AsyncResult.Pending<String>()
val failure = AsyncResult.Failure<String>(IllegalStateException("Failure reason"))
val success = AsyncResult.Success("success value")

// Check type.
val isPending = result is AsyncResult.Pending
val isFailure = result is AsyncResult.Failure
val isSuccess = result is AsyncResult.Success
val isCompleted1 = result !is AsyncResult.Pending
val isCompleted2 = result is AsyncResult.Failure || result is AsyncResult.Success

// Retrieve success values.
val success1 = success.value // Type is 'String'
val success2 = (result as? AsyncResult.Success)?.value // Type is 'String?' conditioned on if the result is a success.

// Retrieve failure reason.
val error1 = failure.error // Type is 'Throwable'
val error2 = (result as? AsyncResult.Failure)?.error // Type is 'Throwable?' conditioned on if the result is a failure.

// Generic type check.
when (result) {
  is AsyncResult.Pending { /* Do something in the pending case, such as showing a loading indicator. */ }
  is AsyncResult.Failure { /* Do something with result.error which is never null. */ }
  is AsyncResult.Success { /* Do something with result.value which is always defined. */ }
  // 'else' can't exist since all cases are exhausted, and Kotlin will eventually produce an error if sealed class 'when's aren't exhaustive.
}

// Note 'getOrThrow' is no longer needed since 'value' can only be retrieved if the result is confirmed to be a success.
// Similarly, 'getErrorOrNull' isn't needed since the error can similarly only be extracted from a Failure result.
// 'getOrDefault' is still possible using patterns as so (where the second is preferred to ensure all cases are considered):
val defaultExample1 = if (result is AsyncResult.Success) result.value else default
val defaultExample2 = when (result) {
  // Or, split out 'failure' to log an error message.
  is AsyncResult.Pending, is AsyncResult.Failure -> default
  is AsyncResult.Success -> result.value
}

// Note that result transformations haven't changed at all.
```

The main advantages of the new approach:
- All type cases must always be considered when using 'when' with the result (forcing consideration of both error and pending cases--this is useful since we often ignore pending cases today despite them existing and occurring)
- There's no longer any question about the presence of success values or failure error throwables (they are always present if the corresponding result is the correct type) which results in safer, more readable, and shorter code
- The implementation properly allows for null success values (see 'rationale' section below)

The only disadvantage is that some generic cases will conflate ``AsyncResult``'s sub-types, such as this case:

```kotlin
val results1 = mutableListOf(AsyncResult.Pending())
// results1 is of type MutableList<AsyncResult.Pending>, but this can be fixed by being explicit:
val results2 = mutableListOf<AsyncResult<String>>(AsyncResult.Pending())
// Or:
val results3: MutableList<AsyncResult<String>> = mutableListOf(AsyncResult.Pending())
```

### Rationale for why this PR is needed & connection to algebraic expressions
#4239 introduces changes to ``QuestionAssessmentProgressController`` and ``ExplorationProgressController`` such that data providers with null payloads are transformed into others. However, that caused an issue when transforming results since 'null' can mean either the absence of 'success' (i.e. a failure) or a successful null value, and ``AsyncResult`` couldn't tell the difference between these without leveraging a sealed class.

See #4239 for why it's necessary for the broader algebraic expressions work (which is the same justification as why this PR is). This PR exists to make #4239 smaller since it brought in some additional refactoring & cleanup beyond the minimal migration to a sealed class. Furthermore, this included in the algebraic project chain for the same reason as #4239: to simplify merging and reviews.

### Tests migration and ``DataProviderMonitorFactory``
Rather than updating all tests which verified ``DataProvider`` results to use the new ``AsyncResultSubject``, it seemed nicer to migrate them over to ``DataProviderMonitorFactory`` (which effectively fully fixed #3813). This resulted in a nice simplification in a lot of test suites by eliminating Mockito usage entirely (except in the monitor's implementation). I also replaced all ``toLiveData``-esque calls to use ``DataProvider``s, instead (which required changing a bunch of controllers over to using ``DataProvider``s instead of ``LiveData`` (which is the preferred approach since ``LiveData`` should never be used in the domain layer to ensure good threading cohesion).

### Test exemptions & changes
Note that there's a new ``AsyncResultSubject`` being introduced here to simplify testing (which consequently fixes #92), but tests aren't added for this subject for similar reasons to past algebraic expression PRs. #4236 was filed to track adding tests for this subject in the future. All existing cases that weren't migrated as part of the monitor factory refactor were moved over to using this new subject (except those explicitly testing ``AsyncResult``).

A bunch of tests have been removed since they are no longer possible due to compile-time guarantees about the value of ``AsyncResult`` in different scenarios.

``StateFragmentTest`` was updated to account for the content description for incorrect answers to not be computed correctly (see below section for details).

### Changes to ``StateRecyclerViewAssembler`` & content descriptions
There was a bug in ``StateRecyclerViewAssembler`` where an answer wouldn't be indicated as incorrect correctly in explorations. I fixed this by introducing a more explicit 'correct_answer' signal in the answer response proto. This fix was needed since one of ``StateFragmentTest``'s tests started failing when another issue was fixed in ``ExplorationProgressControllerTest``: in an old PR, one of the notifications for the current state ``DataProvider`` was dropped mid-answer submission. Restoring this notification triggered the test to correctly fail (due to it actually hitting the bug in the assembler; before, the content description wasn't being correctly defined in that test and it was falsely passing). The fix to the assmbler caused the test to start passing (but another to fail due to it not being supported on Robolectric; it's been subsequently ignored like others of its kind).

The new fix is intentionally designed to be robust against cases when an answer doesn't have a correct label (since that was assumed to be present before).

## Essential Checklist
- [x] The PR title and explanation each start with "Fix #bugnum: " (If this PR fixes part of an issue, prefix the title with "Fix part of #bugnum: ...".)
- [x] Any changes to [scripts/assets](https://github.com/oppia/oppia-android/tree/develop/scripts/assets) files have their rationale included in the PR explanation.
- [x] The PR follows the [style guide](https://github.com/oppia/oppia-android/wiki/Coding-style-guide).
- [x] The PR does not contain any unnecessary code changes from Android Studio ([reference](https://github.com/oppia/oppia-android/wiki/Guidance-on-submitting-a-PR#undo-unnecessary-changes)).
- [x] The PR is made from a branch that's **not** called "develop" and is up-to-date with "develop".
- [x] The PR is **assigned** to the appropriate reviewers ([reference](https://github.com/oppia/oppia-android/wiki/Guidance-on-submitting-a-PR#clarification-regarding-assignees-and-reviewers-section)).

## For UI-specific PRs only
N/A -- This should be a non-side effect change. Despite the UI changes, it shouldn't actually change user behaviors (possibly with the exception of answer notification being a bit faster which led to the UI test fix that was explained above) with one primary exception: this fixes the content description computation for incorrect answers. **Reviewers:** please let me know if you'd like this demonstrated, and how. I also didn't explicitly verify that affected shared tests pass on Espresso, but I highly doubt they wouldn't (or at least, would change their current pass/fail status) given that their Robolectric counterparts pass and this is a non-functional change.

I did not verify StateFragmentTest on Espresso since it's currently broken (see #4238). This is fixed in the next PR where the test suite is verified to pass.

Commit history:

* Alphabetize test exemptions.

* Fix typo & add regex check.

The new regex check makes it so that all parameterized testing can be
more easily tracked by the Android TL.

* Add missing KDocs.

* Post-merge cleanups.

Also, fix text file exemption ordering.

* Add new test for negation with math symbol.

* Post-merge fixes.

* Add KDocs.

Also, add new regex exemption for new parameterized tests in this
branch.

* Refactor & simplify real ext impl.

Also, fix/clarify some KDocs.

* Lint fixes.

* Simplify operation list converter a lot.

This inlines three recursive operations to be done during the actual
computation to simplify the overall converter complexity (and to make
determining the test matrix easier).

* Prepare for new tests.

* Remove the ComparableOperationList wrapper.

* Change parameterized method delimiter.

* Use utility directly in test.

* Post-merge fixes.

This adjusts for the removal of ComparableOperationList (i.e. no wrapper
proto).

* Add first round of tests.

This includes fixes to the converter itself as it wasn't distributing
both product inversions and negation correctly in several cases. Tests
should now be covering these cases.

* Finish initial test suite.

Still needs to be cleaned up, but after converter refactoring attempts.

* Simplify operation sorting comparators.

* Remove old tests.

* Add remaining missing tests.

* KDocs & test exemption.

* Renames & lint fixes.

* Post-merge fixes.

* Add tests.

* KDocs + exemptions.

Also, clean up polynomial sorting.

* Lint fixes.

* Post-merge fixes.

Also, mark methods/classes that need tests.

* Add extension tests.

* Add classifier tests.

* Use more intentional epsilons for float comparing.

* Treat en-dash as a subtraction symbol.

* Add explicit platform selection for paramerized.

This adds explicit platform selection support rather than it being
automatic based on deps. While less flexible for shared tests, this
offers better control for tests that don't want to to use Robolectric
for local tests.

This also adds a JUnit-only test runner, and updates MathTokenizerTest
to use it (which led to an almost 40x decrease in runtime).

* Exemption fixes.

Also, fix name for the AndroidJUnit4 runner.

* Remove failing test.

* Fix unary expression precedence.

Also, use ParameterizedJunitTestRunner for MathExpressionParserTest.

* Fixes & add more test cases.

* Post-merge fixes & test changes.

Also, update RealExtensionsTest to use the faster JUnit runner.

* Use utility directly in LaTeX tests.

* Post-merge fixes.

Also, update ExpressionToComparableOperationConverterTest to use the
fast JUnit-only runner.

* Post-merge fixes.

Also, update PolynomialExtensionsTest to use fast JUnit-only runner.

* Post-merge fixes.

Also, update float interval per new tests.

* Lint & other check fixes.

* Replace deprecated term.

* Post-merge fixes.

* Add full test suites for alg exp classifiers.

* Lint & static check fixes.

* Fix test on Gradle.

* Fix test for Gradle.

* Add tests for math equations.

And, post-merge fixes.

* Static check & lint fixes.

* Post-merge fixes.

Verified CI checks & all unit tests are passing.

* Split up tests.

Also, adds dedicated BUILD.bazel file for new test.

* Add missing test in Bazel, and fix it.

* Correct order for genrule.

* Add full test suite.

* Clean up + KDocs + exemption.

* Lint fixes.

* Post-merge fix.

* Cache KotliTeX renders.

Directly rendering LaTeX through KotliTeX is way too slow, so this
introduces a custom flow through Glide that computes a PNG for the LaTeX
on a background thread and then caches it as part of Glide's cache to
speed up re-renders of the LaTeX. We may need to manage/prune the cache
over time, but for now we'll just rely on Glide's internal behaviors.

This also documents some new tests that should be added, but it's not
comprehensive.

* Add tests, docs, and exemptions.

* Update to fixed version of KotliTeX.

The newer version correctly computes the bounds for rendered LaTeX.

* Lint fixes.

* Add new dependency licenses.

This isn't done yet (some of the licenses still need to be fixed).

* Fix license links.

Note that the kxml one was tricky since its Maven entry says it's
licensed under BSD and CC0 1.0, and its SourceForge link says the same
plus LGPL 2.0. However, the source code and GitHub version of the
project license it under MIT, and this seems to predate the others so
it seems like the most correct license to use in this case and the one
that we're using to represent the dependency.

* Fix Gradle build.

This uses a version of KotliTeX that builds correctly on Jitpack for Gradle,
and fixes the StaticLayout creation to use an alignment constant that
builds on Gradle (I'm not sure why there's a difference here between
Gradle & Bazel, but the previous constant isn't part of the enum per
official Android docs).

* Create the math drawable synchronously.

This requires exposing new injectors broadly in the app since the math
model loader doesn't have access to the dependency injection graph
directly.

* Remove new deps from Maven list.

They were incorrectly pulled in by KotliTeX.

* Add argument partitioning.

This fixes cases where argument calls may be very large and fail to
execute due to exceeding system limitations.

* Make allowance for empty cases to fix tests.

These tests correspond to real scenarios.

* Lint fixes.

* Address reviewer comment.

Clarifies the documentation in the test runner around parameter
injection.

* Fix broken build.

* Fix broken build post-merge.

* Fix broken post-merge classifier.

* Address reviewer comment.

* Post-merge build fixes.

* Post-merge build fixes for new classifiers.

* Post-merge build fixes.

* Correct reference document link.

* Ensure LaTeX isn't stretched or cut-off.

The comments in-code have much more specifics on the approach.

* Add and fix missing test (was broken on Gradle).

* Refactor AsyncResult into a sealed class.

This also introduces an AsyncResultSubject, and more or less fully fixes
issue #3813 in all tests.

This is a cherry-pick from the fix-progress-controller-deadlock branch
since it ended up being quite large (it made more sense to split it into
a pre-requisite PR).

Conflicts:
	app/src/main/java/org/oppia/android/app/player/state/testing/StateFragmentTestActivityPresenter.kt
	domain/src/main/java/org/oppia/android/domain/exploration/ExplorationProgressController.kt
	domain/src/main/java/org/oppia/android/domain/question/QuestionAssessmentProgressController.kt
	domain/src/test/java/org/oppia/android/domain/exploration/lightweightcheckpointing/BUILD.bazel
	testing/src/main/java/org/oppia/android/testing/data/DataProviderTestMonitor.kt
	utility/src/main/java/org/oppia/android/util/data/DataProviders.kt

* Post-merge fixes and updates for consistency.

* Post-merge fixes.

* TODO has been addressed.

* Fix documentation & add tests.

* Lint fixes.

* Fix gradle tests.

I've verified in this commit that all Gradle tests build & run locally
(at least on Robolectric).

* Post-merge fix.

* More post-merge fixes.

* Fix TODO comment.

* Post-merge lint fixes.

* Post-merge fix.

* Fix exploration routing issue.

The underlying problem was that the PR inadvertently changed the
behavior of comparing two results wherein results of different times
would be considered different and be re-delivered (which happened to
break exploration routing, and likely a variety of other places).

This introduces a new method for checking equivelance rather than
confusingly assuming that users of AsyncResult don't care about the
result's time during comparison checking.

New tests have been added to verify the functionality works as expected
(and fails when expected), and I manually verified that the exploration
routing issue was fixed. More details on the specific user-facing issue
will be added to the PR as a comment.

* Update KotliTeX version.

This version doesn't have debug drawing enabled.
@BenHenning BenHenning changed the title Fix #3622, #4238, #3861, part of #4044: Fix state player deadlock by migrating progress controllers over to a command-queue structure [Blocked: #4237] Fix #3622, #4238, #3861, part of #4044: Fix state player deadlock by migrating progress controllers over to a command-queue structure Mar 27, 2022
@BenHenning BenHenning removed the request for review from rt4914 March 27, 2022 05:47
@BenHenning
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Going ahead and merging this per prior discussion with @vinitamurthi since it's high priority for the upcoming alpha release (#4265 is tracking reviewing this as a follow-up after merging).

@BenHenning BenHenning merged commit df0f064 into develop Mar 27, 2022
@BenHenning BenHenning deleted the fix-progress-controller-deadlock branch March 27, 2022 06:59
BenHenning added a commit that referenced this pull request Mar 27, 2022
…ns (#2173)

## Explanation
Fixes #4044

This PR introduces the UI interaction views for numeric expressions, algebraic expressions, and algebraic equations, finishing the initial implementation of the broader math expressions project. This work unblocks adding support for 4 additional topics in the app: Multiplication (support was lost after Alpha MR2 due to a change that added numeric expression questions), Addition & Subtraction, Division, and Expressions & Equations.

This PR finishes a long chain of PRs that were needed to provide the domain functionality to support these new interactions, as a significant amount of mathematics functionality needed to be added including:
- Support for representing generic math expressions/equations, polynomials, and reals
- Support for parsing math expressions
- Support for converting between math expressions and:
  - LaTeX (for rendering)
  - Human-readable sentences (for accessibility)
  - Polynomials and real-value evaluation (for equivalence checking)
  - Comparable structures to verify that two expressions/equations match irrespective of associativity or commutativity order
- Robust error detection to support nearly 2 dozen special cased errors with potential for countless more if needed to ensure users receive excellent feedback when inputting expressions

All of the above also required thorough testing to ensure correctness. See the previous PRs corresponding to #4044 for the full context, and thorough PR descriptions explaining past changes.

From a UI perspective, this PR is introducing:
- The new interaction views and relevant view models, including the logic for constructing and displaying errors for invalid answers
- Support for playing a custom content description for math expression answers so that screenreader users can better understand the expression they've entered
- Support for rendering the LaTeX representation of entered expressions
- A new developer options menu to provide support to input arbitrary expressions and equations and convert them to different outputs to test the underlying math engine that's been built (though it can't yet test the classifiers, but it provides enough information to verify the more complex bits behind the classifiers)

From a functional perspective, this PR is introducing:
- Support for loading JSON explorations that include math expressions
- A new test exploration that's been added to test topic 0 to demonstrate all three interactions and each of those interaction's classifiers (9 total states have been added)

The above, and more, are explained in more detail below.

### Background on UI implementation for new interactions

The UI implementation leverages a single new interaction view & model for all three new interaction types since they are very similar to one another, including handling accessibility and LaTeX rendering cases. The customization arguments, however, don't exactly match so there are some inconsistencies there.

### Background on parsing approach
The new interactions rely on custom math infrastructure for parsing math expressions since no suitable libraries were found that were both license compatible and didn't leverage native code. While this significantly increases the scope of code that needs to be maintained in the project, it has the added benefit of leveraging extremely specific functionality to reduce inconsistencies with Oppia web and ensure a very high quality learner experience when it comes to answer classification and error detection.

Expressions are constructed using an LL(1) recursive-descent parser with early-exit error detection (see the [technical specification](https://docs.google.com/document/d/1JMpbjqRqdEpye67HvDoqBo_rtScY9oEaB7SwKBBspss/edit)). Parsing first goes through an LL(1) lazy tokenization process before being parsed lazily into proto-defined math expression/equation structures. Classifier needs are satisified through custom infrastructure that can evaluate numeric expressions to a single real value, compare math expressions/equations with floating point error correction, compare math expressions/equations irrespective of operation associativity and commutativity by transforming it to an intermediary representation, and can compare expressions/equations for equivalence by first converting it to a polynomial using a custom nearly fully feature complete polynomial system. Finally, UI-specific needs are satisified through generators for both LaTeX and human-readable accessibility strings.

The preceding PRs in this project contain the implementations for parsing, conversion, and comparsion and include PR descriptions that explain these systems & other peripheral changes in great detail.

### PR history
This PR contains **all** of the PRs corresponding to both the previous attempt at implementing math expressions, and the latest (since all commits end up being duplicated in PR chains). There's also some early work that preceded the original work in this PR that's included in its history (it goes back quite a bit).

For reference, here's the entire chain of PRs in order that precede this one for implementing math expressions support:
1. #4045
2. #4046
3. #4047
4. #4049
5. #4050
6. #4051
7. #4052
8. #4054
9. #4055
10. #4056
11. #4057
12. #4058
13. #4059
14. #4061
15. #4063
16. #4068
17. #4237
18. #4239

### Refactors, miscellaneous changes, and future work
All interaction view models were refactored to use a factory pattern rather than a function to improve readability, and to make that view model construction consistent with other similar situations (i.e. cases where new instances need to be created with Dagger dependencies).

Split screen supported interaction IDs have been refactored to be a Dagger set to avoid a direct dependency on InteractionViewModelModule to access the IDs (the new solution is more Dagger 2 idiomatic).

This PR doesn't finish all aspects of the project as there are a number of improvements that have been proposed toward the end of development. These have been cataloged in #4254 and will be implemented in a follow-up PR (but will only be started after this PR & its predecessors have been merged). None of those work items block the overall project, and are intentionally being delayed to a future work item to ensure that math expressions can land more quickly.

### Test specifics & exemptions
Changes were needed in ``EditTextInputAction`` to support inputting Unicode text (which is necessary for some UI tests that verify using math symbols such as for times and divide). Espresso itself doesn't support inputting these characters (presumably since it can't easily find them on the keyboard), so the action now exposes an option to directly set the text.

Exemption explanations:
- ``MathExpressionInteractionsViewTest``: this has been enabled to allow parameterized tests to ensure it can verify a broad set of questions and answers. This might actually be a nice pattern to follow for other interaction tests in the future.
- All test exemptions are either can't be obviously tested (listeners & annotations), are tested through other suites (view models & presenters), is especially difficult to test (``ParameterizedAutoAndroidTestRunner``), or is deemed not important enough to add tests for due to a trivial implementation and in the effort to finish this project sooner (``SplitScreenInteractionModule``).

Note that the defaulting cases for accessibility strings & LaTeX (i.e. the scenarios where generation to either fails) can't easily be tested since the scenarios in which generation fails arise from invalid answers that can't be submitted since they trigger submit-time errors. However, the failure cases for both of these utilities have been thoroughly checked in their respective test suites.

This PR also introduces a new addition to ``OppiaParameterizedTestRunner``: ``ParameterizedAutoAndroidTestRunner``. This runner acts like ``AndroidJUnit4`` wherein it will automatically select a Robolectric or Espresso runner depending on the current runtime environment. This ought to only be used by shared tests that are supposed to run on both platforms, otherwise Robolectric or Espresso specific runners should be used (or JUnit for non-Robolectric tests).

## Essential Checklist
- [x] The PR title and explanation each start with "Fix #bugnum: " (If this PR fixes part of an issue, prefix the title with "Fix part of #bugnum: ...".)
- [x] Any changes to [scripts/assets](https://github.com/oppia/oppia-android/tree/develop/scripts/assets) files have their rationale included in the PR explanation.
- [x] The PR follows the [style guide](https://github.com/oppia/oppia-android/wiki/Coding-style-guide).
- [x] The PR does not contain any unnecessary code changes from Android Studio ([reference](https://github.com/oppia/oppia-android/wiki/Guidance-on-submitting-a-PR#undo-unnecessary-changes)).
- [x] The PR is made from a branch that's **not** called "develop" and is up-to-date with "develop".
- [x] The PR is **assigned** to the appropriate reviewers ([reference](https://github.com/oppia/oppia-android/wiki/Guidance-on-submitting-a-PR#clarification-regarding-assignees-and-reviewers-section)).

## For UI-specific PRs only
I've verified the interaction with the accessibility scanner locally and it didn't mention any new suggestions (there was one suggestion on the label for the input box when inputting something, and another for the congratulations banner contrast--both of which are existing issues that affect other interactions).

### Screenshots of new UIs
| Device type | Language | Orientation | Input box | Error | Inputted answer |
|-------------|----------|-------------|-----------|-----------------|-------|
| Handset     | English  | Portrait    | ![image](https://user-images.githubusercontent.com/12983742/158960886-b66b5f59-48e9-4005-a05d-60cdc9917cee.png)      | ![image](https://user-images.githubusercontent.com/12983742/158966282-108719be-44cb-42ab-8570-fe2f4dd49cfe.png) | ![image](https://user-images.githubusercontent.com/12983742/158966035-c1db8ee1-01a8-4e2f-bab7-c9622965c5b5.png)        |
| Handset     | English  | Landscape   | ![image](https://user-images.githubusercontent.com/12983742/158966436-ef289ea9-2b69-4bd8-b07a-8e0ac917f30a.png)      | ![image](https://user-images.githubusercontent.com/12983742/158966626-8a19d38c-2cbe-4544-aab1-57da419ca405.png)            | ![image](https://user-images.githubusercontent.com/12983742/158966701-768af358-912c-44c4-8c20-e82db23b39a7.png)  |
| Handset     | Arabic   | Portrait    |  ![image](https://user-images.githubusercontent.com/12983742/158967405-29461acf-d160-46e2-bbaa-233a97b99f91.png)     | ![image](https://user-images.githubusercontent.com/12983742/158967611-d3494512-ff49-4c3e-988d-3c2a0eb48943.png)            | ![image](https://user-images.githubusercontent.com/12983742/158969001-a5d516bb-7db2-49f3-b614-baf298c0ce95.png)  |
| Handset     | Arabic   | Landscape   | ![image](https://user-images.githubusercontent.com/12983742/158969671-f2f92523-6045-4908-9b3a-c0efec525e55.png)      | ![image](https://user-images.githubusercontent.com/12983742/158970091-ba858e7e-deab-4189-b06a-91208049ab79.png)            | ![image](https://user-images.githubusercontent.com/12983742/158971054-c64adfbd-06a1-4cc7-a3df-983793e8bd30.png)  |
| Tablet      | English  | Portrait    | ![image](https://user-images.githubusercontent.com/12983742/158975533-046a1d31-145a-4671-b212-6770f0b09b4a.png)      | ![image](https://user-images.githubusercontent.com/12983742/158975620-e404da29-630b-4a19-be8b-13ff5b853601.png)            | ![image](https://user-images.githubusercontent.com/12983742/158975673-a20f6ddb-1669-4035-a819-c23eccee666b.png)  |
| Tablet      | English  | Landscape   | ![image](https://user-images.githubusercontent.com/12983742/158975794-c36f7bee-4f47-4683-b3a2-7e012ea7039c.png)      | ![image](https://user-images.githubusercontent.com/12983742/158975835-a43957f8-c831-4fe3-a69e-3df7b6be3013.png)            | ![image](https://user-images.githubusercontent.com/12983742/158975869-59a7b989-83c1-4162-9df6-6d07f79c5005.png)  |
| Tablet      | Arabic   | Portrait    |  ![image](https://user-images.githubusercontent.com/12983742/158976398-55014bf8-0146-4507-95a3-733fab00f36f.png)     | ![image](https://user-images.githubusercontent.com/12983742/158976477-0736e4c3-81c0-42fd-8160-6ba0cb528e44.png)            | ![image](https://user-images.githubusercontent.com/12983742/158976579-b0a834fc-793e-4205-a2ad-c4029665430d.png)  |
| Tablet      | Arabic   | Landscape   | ![image](https://user-images.githubusercontent.com/12983742/158976744-7c2fb78b-7338-4688-94a0-afa65126b972.png)      | ![image](https://user-images.githubusercontent.com/12983742/158976832-43aee849-38fe-4fb7-8ebf-af13e0cb5cb0.png)            | ![image](https://user-images.githubusercontent.com/12983742/158976882-4e309290-63ab-4ea3-a3a6-39f64615afe4.png)  |

Note that the interaction's errors haven't yet been translated. Also, some work may need to be done in the future to ensure directionality makes sense both for input and rendering (asking folks yielded that input is typically right-to-left but math expressions are still represented left-to-right, so it's not clear if math input should also be left-to-right). In the case above, the text view actually switches the '+2' to '2+1' once it has another number since the context is more complete. It's possible RTL users are already used to quirks like this. It's also likely the custom math keyboard would be a good means of solving this issue long-term.

Screenshot of the new developer options menu for testing math expressions/equations:
![math_expressions_debug_menu](https://user-images.githubusercontent.com/12983742/158933786-9654c85e-b7b9-49fa-8e5f-8d37e598139f.png)

Note that I didn't bother to screenshot other configurations for the developer options menu since it's only visible to developers, so it's less important to make sure it meets the accessibility, language, device, and orientation requirements that the other screens of the UI are held to.

### Videos
| Flow being demonstrated                                    | Video recording |
|------------------------------------------------------------|-----------------|
| Submitting numeric expressions answers                     | https://user-images.githubusercontent.com/12983742/158933258-74992080-a9ec-46da-b752-c00b406ab3ec.mp4            |
| Submitting algebraic expressions answers                   | https://user-images.githubusercontent.com/12983742/158933296-0ea70704-9e3b-4e0d-9150-680a47f9ece2.mp4            |
| Submitting answers that cause errors                           | https://user-images.githubusercontent.com/12983742/158933391-602356c3-ccad-4199-8c0b-47d42abd7896.mp4            |
| Rendering fractions vs. divisions                          | https://user-images.githubusercontent.com/12983742/158933425-9abc640b-289e-484f-8f30-dab38789c99e.mp4            |
| Submitting numeric expressions with a screenreader enabled | https://user-images.githubusercontent.com/12983742/158933446-21afbcd6-0ea8-4558-8c68-9fa0157a7e3d.mp4            |
| Submitted math equations with a screenreader enabled       | https://user-images.githubusercontent.com/12983742/158933460-ddf39ba3-1fd8-4bfc-82e9-cc1845846646.mp4            |

### Espresso test results
| ![final_math_pr_developeroptionsactivitytest_passing](https://user-images.githubusercontent.com/12983742/158932650-4c55fd70-0c58-4972-b1c9-dda727190f9a.png) | ![final_math_pr_developeroptionsfragmenttest_passing](https://user-images.githubusercontent.com/12983742/158932667-9ab52468-6c7d-4088-8e80-3e71afe3cc29.png) |
|------|------|
| ![final_math_pr_htmlparsertest_passing](https://user-images.githubusercontent.com/12983742/158932678-aadd0ba5-f7c4-49e0-b7a8-0cf0734a269d.png) | ![final_math_pr_mathexpressioninteractionsviewtest_passing](https://user-images.githubusercontent.com/12983742/158932687-e1b5df4a-9a5e-4f5e-a0bb-0b1e60ce562e.png) |
| ![final_math_pr_mathexpressionparseractivitytest_passing](https://user-images.githubusercontent.com/12983742/158932699-e71b0b5a-f4c6-475c-9cc1-db626de9ed51.png) | ![final_math_pr_mathexpressionparserfragmenttest_passing](https://user-images.githubusercontent.com/12983742/158932712-a68cee27-4a2f-49ab-895b-f2d021cbc3d8.png) |
| ![final_math_pr_questionplayeractivitytest_passing](https://user-images.githubusercontent.com/12983742/158932734-e9aefddf-13e9-4cf6-9a22-37588ca527e7.png) | ![final_math_pr_statefragmenttest_passing](https://user-images.githubusercontent.com/12983742/158932752-3bc3d821-b703-46a9-a5ef-29fd568d896f.png) |

Note that in the case of ``MathExpressionInteractionsViewTest`` this is the first PR that demonstrates using parameterized tests with Espresso.

Commit history:

* Treat en-dash as a subtraction symbol.

* Add explicit platform selection for paramerized.

This adds explicit platform selection support rather than it being
automatic based on deps. While less flexible for shared tests, this
offers better control for tests that don't want to to use Robolectric
for local tests.

This also adds a JUnit-only test runner, and updates MathTokenizerTest
to use it (which led to an almost 40x decrease in runtime).

* Exemption fixes.

Also, fix name for the AndroidJUnit4 runner.

* Remove failing test.

* Fix unary expression precedence.

Also, use ParameterizedJunitTestRunner for MathExpressionParserTest.

* Fixes & add more test cases.

* Post-merge fixes & test changes.

Also, update RealExtensionsTest to use the faster JUnit runner.

* Use utility directly in LaTeX tests.

* Post-merge fixes.

Also, update ExpressionToComparableOperationConverterTest to use the
fast JUnit-only runner.

* Post-merge fixes.

Also, update PolynomialExtensionsTest to use fast JUnit-only runner.

* Post-merge fixes.

Also, update float interval per new tests.

* Lint & other check fixes.

* Replace deprecated term.

* Post-merge fixes.

* Add full test suites for alg exp classifiers.

* Lint & static check fixes.

* Fix test on Gradle.

* Fix test for Gradle.

* Add tests for math equations.

And, post-merge fixes.

* Static check & lint fixes.

* Post-merge fixes.

Verified CI checks & all unit tests are passing.

* Split up tests.

Also, adds dedicated BUILD.bazel file for new test.

* Add missing test in Bazel, and fix it.

* Correct order for genrule.

* Add full test suite.

* Clean up + KDocs + exemption.

* Lint fixes.

* Post-merge fix.

* Cache KotliTeX renders.

Directly rendering LaTeX through KotliTeX is way too slow, so this
introduces a custom flow through Glide that computes a PNG for the LaTeX
on a background thread and then caches it as part of Glide's cache to
speed up re-renders of the LaTeX. We may need to manage/prune the cache
over time, but for now we'll just rely on Glide's internal behaviors.

This also documents some new tests that should be added, but it's not
comprehensive.

* Add tests, docs, and exemptions.

* Update to fixed version of KotliTeX.

The newer version correctly computes the bounds for rendered LaTeX.

* Lint fixes.

* Add new dependency licenses.

This isn't done yet (some of the licenses still need to be fixed).

* Fix license links.

Note that the kxml one was tricky since its Maven entry says it's
licensed under BSD and CC0 1.0, and its SourceForge link says the same
plus LGPL 2.0. However, the source code and GitHub version of the
project license it under MIT, and this seems to predate the others so
it seems like the most correct license to use in this case and the one
that we're using to represent the dependency.

* Fix Gradle build.

This uses a version of KotliTeX that builds correctly on Jitpack for Gradle,
and fixes the StaticLayout creation to use an alignment constant that
builds on Gradle (I'm not sure why there's a difference here between
Gradle & Bazel, but the previous constant isn't part of the enum per
official Android docs).

* Create the math drawable synchronously.

This requires exposing new injectors broadly in the app since the math
model loader doesn't have access to the dependency injection graph
directly.

* Remove new deps from Maven list.

They were incorrectly pulled in by KotliTeX.

* Add argument partitioning.

This fixes cases where argument calls may be very large and fail to
execute due to exceeding system limitations.

* Post-merge fixes.

Note that only the following tests are failing (some of which may be due
to the previous branch):
- MarkChaptersCompletedFragmentTest
- MarkStoriesCompletedFragmentTest
- StoryProgressTestHelperTest
- ModifyLessonProgressControllerTest
- TopicListControllerTest
- ComputeAffectedTestsTest
- MarkTopicsCompletedFragmentTest
- HomeActivityTest

* Make allowance for empty cases to fix tests.

These tests correspond to real scenarios.

* Lint fixes.

* Fix broken tests and add reasonable exemptions.

* First pass at adding tests.

Some debugging left, and more tests to add.

This also adds auto-switching support for parameterized tests.

* Fix DeveloperOptionsActivityTest.

Also, fix all other test builds (for Gradle). This will probably require
some reformatting.

* Add & fix remaining tests.

This also fixes a bug where the correct answer a11y label was being
incorrectly assumed to be the correct answer even for incorrect cases.

* Add docs & clean up remaining non-lint parts.

* Lint & small breakage fixes.

* Fix broken tests.

* Address reviewer comment.

Clarifies the documentation in the test runner around parameter
injection.

* Fix broken build.

* Fix broken build post-merge.

* Fix broken post-merge classifier.

* Address reviewer comment.

* Post-merge build fixes.

* Post-merge build fixes for new classifiers.

* Post-merge build fixes.

* Correct reference document link.

* Ensure LaTeX isn't stretched or cut-off.

The comments in-code have much more specifics on the approach.

* Add and fix missing test (was broken on Gradle).

* Fix Gradle tests.

This commit has verified the following tests now pass on Espresso:
- MathExpressionInteractionsViewTest
- HtmlParserTest
- MathExpressionParserActivityTest
- MathExpressionParserFragmentTest
- DeveloperOptionsActivityTest
- DeveloperOptionsFragmentTest

StateFragmentTest is having issues (it ends up hanging), so further
investigation is needed.

* Update to newer version of Kotlin coroutines.

This version includes StateFlow which will be a really useful mechanism
for helping to avoid using critical sections.

* First attempt to fix deadlock.

This uses StateFlows and an actor to avoid the deadlock.

This is missing necessary hint changes that are coming in a later
commit. Tests currently fail, and questions haven't yet been migrated
(and won't until the fixes are verified).

* Attempt to make hint handler multi-threadable.

This is a midway solution that's being committed for posterity, but will
be reverted in favor of a solution that forces hint handler to be unsafe
across multiple threads (since it's much simpler, and works given that
all users of it now synchronize state management using an actor).

* Finish fixing state player.

This includes a fix for accessibility string handling (since the new
flow triggers one of these to fail). It also adds a Bazel file for
StateFragmentTest (I spent some time trying to get Espresso tests
working with Bazel but ran into a compatibility issue).

StateFragmentTest has been verified to pass on Robolectric and Espresso
with this change.

This sets up the project for fixing questions in the next commit.

* First pass on migrating question controller.

This also includes a migration for exploration & question domain tests
to use the test monitor utility.

The question tests currently fail since there's a bug in AsyncResult
where it won't support null values during transformations.

* Refactor AsyncResult into a sealed class.

This also introduces an AsyncResultSubject, and more or less fully fixes
issue #3813 in all tests.

* Refactor AsyncResult into a sealed class.

This also introduces an AsyncResultSubject, and more or less fully fixes
issue #3813 in all tests.

This is a cherry-pick from the fix-progress-controller-deadlock branch
since it ended up being quite large (it made more sense to split it into
a pre-requisite PR).

Conflicts:
	app/src/main/java/org/oppia/android/app/player/state/testing/StateFragmentTestActivityPresenter.kt
	domain/src/main/java/org/oppia/android/domain/exploration/ExplorationProgressController.kt
	domain/src/main/java/org/oppia/android/domain/question/QuestionAssessmentProgressController.kt
	domain/src/test/java/org/oppia/android/domain/exploration/lightweightcheckpointing/BUILD.bazel
	testing/src/main/java/org/oppia/android/testing/data/DataProviderTestMonitor.kt
	utility/src/main/java/org/oppia/android/util/data/DataProviders.kt

* Post-merge fixes and updates for consistency.

* Post-merge fixes.

* TODO has been addressed.

* Fix documentation & add tests.

* Lint fixes.

* Lint & post-merge fixes.

Questions-related tests still fail and need to be fixed now that
AsyncResult has been refactored to support null values.

* Post-merge test fixes.

The core affected UI/domain tests have now been verified as working on
Robolectric. The full test suite is next.

* Add documentation & tests.

Also, fix a bug in the automatic StateFlow DataProviders wherein they
wouldn't notify correctly on changes. This led to some simplifications
in the exploration & question progress controllers.

* Lint fixes.

* Fix gradle tests.

I've verified in this commit that all Gradle tests build & run locally
(at least on Robolectric).

* Fix Proguard build.

This required bringing kotlinx-coroutines-android up-to-date with
kotlinx-coroutines-core (since that was updated on this branch).

New but reasonable Proguard warning exemptions also needed to be added.

* Post-merge fixes.

* Gradle fixes.

This also fixes an issue wherein answers couldn't be resubmitted for
math expression interactions after an error occurred.

* Fix parameterized runners for Espresso.

This fixes a typo when loading the AndroidJUnit4 runner during
parameterization runer selection, and ensures that test names don't
contain illegal characters that would break the runner.

* Post-merge fix.

* More post-merge fixes.

* Fix TODO comment.

* Post-merge lint fixes.

* Post-merge fix.

* Fix exploration routing issue.

The underlying problem was that the PR inadvertently changed the
behavior of comparing two results wherein results of different times
would be considered different and be re-delivered (which happened to
break exploration routing, and likely a variety of other places).

This introduces a new method for checking equivelance rather than
confusingly assuming that users of AsyncResult don't care about the
result's time during comparison checking.

New tests have been added to verify the functionality works as expected
(and fails when expected), and I manually verified that the exploration
routing issue was fixed. More details on the specific user-facing issue
will be added to the PR as a comment.

* Post-merge fixes.

* Post-merge fixes.

The local repo has been verified to pass nearly all static analysis and
lint tests, as well as all Robolectric tests. The developer and alpha
versions of the app build.

* Update KotliTeX version.

This version doesn't have debug drawing enabled.

* Fix lifecycle breakage.

I noticed downstream that quickly navigating back and forth to enter &
exit an exploration can cause the progress controller to get into a bad
state that either leads to a broken experience (stacked explorations or a
blank state), or a crash.

The issue was coming from DataProviders being shared across sessions
even though the underlying state was different. This change ensures that
providers stay completely independent, similar to the core session
state.

* Address reviewer comment.

* Update play session controllers.

This ensures that the command queue itself is fully isolated to avoid
delayed events potentially leaking across sessions (now that the session
ID barrier has been removed).
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