This replaces the --prefer-shared-library flag, which falls back to
regular (non-shared-lib) compile if the NDK is not found, with the
--build-shared-library flag, which exits with an error message if the
NDK is not found.

This simplifies the set of allowed code paths through AOT compile,
resulting in better testability and easier-to-follow logic. It also
results in more predictable behaviour for continuous integration and
other scenarios.

This change adds support for armv7, arm64, and universal iOS apps.

This change eliminates iOS target architecture hardcoding (previously
arm64 only) and uses the target architecture(s) specified in Xcode's
ARCHS setting ('Architectures' in Xcode Build Settings).

For universal binaries, set ARCHS to its default value, $(ARCHS_STANDARD).

Note that after changing the architecture in Xcode, developers should
run 'pod install' from the ios subdirectory of their project. A separate
change (that will land before this one) will add support for
automatically detecting project file and Podfile changes and re-running
pod install if necessary.

This change also adds an --ios-arch option to flutter build aot. In iOS
AOT builds (in profile and release mode), this dictates which
architectures are built into App.framework. This flag should generally
be unnecessary to set manually since flutter build aot is typically only
invoked internally by flutter itself.

There's very little code-sharing between the two, and what little there
is is concentrated in the GenSnapshotClass and the fingerprint
reading/writing utility methods.

Moves the kernel compile step to the beginning of the AOT build in a
separate method. This is pre-factoring for iOS universal builds where
the kernel build happens once, but we then snapshot twice: once for
armv7 and once for arm64.

This also writes dependencies to build/kernel_compile.d rather than
build/aot/snapshot.d, since that is immediately overwritten by
gen_snapshot.

This isn't user-specifiable through a flag, so no need to pass it as a
parameter.

Fixes a bug introduced in 82f969ff where
the depfile used for AOT snapshotting, useful in particular for skipping
gen_snapshot when inputs/outputs haven't changed since the last build.

Inlines the buildAotSnapshot function, which simply passes through its
arguments to Snapshotter.buildAotSnapshot.

This is required for iOS debug builds, but unused otherwise. In theory,
Android debug builds could be run in this mode, but this is historically
untested and adds unnecessary complexity to the code. If ad-hoc testing
is required, it can be patched in when necessary.

This re-lands 8c4f0c0d with a fix to
xcode_backend.sh to eliminate the use of --interpreter.

Requires a fix to xcode_backend.sh. Will followup momentarily with that
fix.

This reverts commit 8c4f0c0d.

This is required for iOS debug builds, but unused otherwise. In theory,
Android debug builds could be run in this mode, but this is historically
untested and adds unnecessary complexity to the code. If ad-hoc testing
is required, it can be patched in when necessary.

This moves AOT snapshotting out of build_aot.dart and into the
Snapshotter class. It also adds unit tests for iOS debug, profile, and
release builds.

This fixes and re-lands 4bb7496b, which
was reverted in ceade39c due to test
failures caused by a bad rebase.

This reverts commit 4bb7496b.

Allows for better mockability when tests are added.

This allows for testing with MemoryFileSystem, when tests are added.

Makes for easier mocking, particularly for testing AOT snapshot build.

Wraps the compile function in a class injected via the global context,
which makes it easier to mock in unit tests -- specifically tests for
AOT snapshotting, which already require pretty significant amounts of
mock inputs.

This replaces the existing manual invocation with the GenSnapshot class,
which allows for better configuration and testability.

* Handle error count reported by frontend.

Extend compilation result from single string to a structure(string filename and integer error count).

* Use ?.

* Include engine roll with dart sdk roll.

* parse(onError) -> tryParse

* Make '?? throw' more readable and avoid issue with analyzer

* Fix test so it mocks compiler output including errors count

We are about to begin building gen_snapshot as a multi-arch binary,
which when run as x86_64 will generate arm64 AOT output, and when run as
i386 will generate armv7 AOT output.

Currently, gen_snapshot is an x86_64 binary, so this change is
effectively preventative in nature, and is a no-op with the current
snapshotter.

* Update dependencies with forced upgrade.

Now that https://github.com/flutter/flutter/issues/15261 is fixed, do the update with upgrade.

* Update test package use following upgrade

* Replace addOption(allowMultiple) with addMultiOption

* Pass entry points JSON files to front-end server (#15180)

* Fix ios/debug build which uses 'flutter build aot': do not require entry points files and disable AOT transformations in this mode

* Revert "Pass entry points JSON files to front-end server (#15180)"

This reverts commit 0edea887.

Reason: buildbot failures on Mac.

* Use depfile in --preview-dart-2 mode.

* Generate and use frontend_server.d to guard against reusing outdated dill files when frontend_server changes.

* Fix snapshot fingerprinting in --preview-dart-2 mode.

This is a follow up to PR #14775 - instead of treating dill file
as an input treat as intermediate file and don't fingerprint it.

Make sure to always use original main Dart file as an entry
point for fingerprint calculation.

This fixes an issue that AOT snapshot would not be recompiled in
the preview-dart-2 mode if entry point changes, e.g.

$ flutter build aot -t t/x.dart --preview-dart-2
$ flutter build aot -t t/y.dart --preview-dart-2

The second invocation would not build AOT snapshot.

(This issue is visible on the microbencmarks bot)

* Fix snapshot fingerprint check for --preview-dart-2.

* Remove printTraces

* Put generated kernel files into <build> directory

* USe default value for kernel file

* Reland 9534082f with fix for incremental compilation.

When in incremental mode, awaiting exitCode won't work because compiler is not expected to exit after compilation.
Instead listen for stdout stream closing and report error if outputFilename has not been received.

* Fix lints

This reverts commit 9534082f.

Causes hot_mode_dev_cycle__preview_dart_2_benchmark test timeout.

* Check frontend_server exit code.

When frontend_server completes abnormally, flutter tools has to stop and let user know.

* Add tests

* Plumb a --strong option through to the front end server and the engine
so that we can run flutter apps in preview-dart-2 and strong mode

* - Address analyzer lint issues
*- correctly set up strong mode option in the case of AOT builds