[flow analysis] Remove ExpressionInfo.after.

Previously, the base `ExpressionInfo` class contained four fields:

- `type`: the type of the expression.

- `ifTrue`: a flow model describing the state of the program after the
  expression is evaluated, assuming the expression evaluates to
  `true`.

- `ifFalse`: a flow model describing the state of the program after
  the expression is evaluated, assuming the expression evaluates to
  `false`.

- `after`: a flow model describing the state of the prorgam after the
  expression is evaluated, making no assumptions about what value the
  expression evaluates to.

The `after` field was largely redundant, since it tracked the same
information as `FlowAnalysisImpl._current`. In fact, flow analysis
contained a substantial amount of code to copy from
`ExpressionInfo.after` to `FlowAnalysisImpl._current`, or vice versa,
in order to keep the two in sync.

The one exception was in `FlowAnalysisImpl.conditional_end`, which is
called at the end of visiting a conditional expression (`e1 ? e2 :
e3`): it joined the `after` flow models from `e2` and `e3` in order to
determine the state of the program after the conditional expression
completes. To preserve this behavior, a small amount of extra
accounting logic had to be added to the handling of conditional
expressions, to keep track of these flow models. (`e2.after` is now
stored in `_ConditionalContext.thenModel`, and `e3.after` comes from
the state of `_current` at the time of entry into
`FlowAnalysisImpl.conditional_end`).

Change-Id: I46e771f8b029550d43a5fe50366177f189a6a91d
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/388081
Commit-Queue: Paul Berry <paulberry@google.com>
Reviewed-by: Kallen Tu <kallentu@google.com>
2 files changed
tree: 7ef257f260e6abc4b092c3f05d48cd80bfaef435
  1. .dart_tool/
  2. .github/
  3. benchmarks/
  4. build/
  5. docs/
  6. pkg/
  7. runtime/
  8. samples/
  9. sdk/
  10. tests/
  11. third_party/
  12. tools/
  13. utils/
  14. .clang-format
  15. .gitattributes
  16. .gitconfig
  17. .gitignore
  18. .gn
  19. .mailmap
  20. .style.yapf
  21. AUTHORS
  22. BUILD.gn
  23. CHANGELOG.md
  24. codereview.settings
  25. CONTRIBUTING.md
  26. DEPS
  27. LICENSE
  28. OWNERS
  29. PATENT_GRANT
  30. PRESUBMIT.py
  31. README.dart-sdk
  32. README.md
  33. sdk.code-workspace
  34. sdk_args.gni
  35. sdk_packages.yaml
  36. SECURITY.md
  37. WATCHLISTS
README.md

Dart

An approachable, portable, and productive language for high-quality apps on any platform

Dart is:

  • Approachable: Develop with a strongly typed programming language that is consistent, concise, and offers modern language features like null safety and patterns.

  • Portable: Compile to ARM, x64, or RISC-V machine code for mobile, desktop, and backend. Compile to JavaScript or WebAssembly for the web.

  • Productive: Make changes iteratively: use hot reload to see the result instantly in your running app. Diagnose app issues using DevTools.

Dart's flexible compiler technology lets you run Dart code in different ways, depending on your target platform and goals:

  • Dart Native: For programs targeting devices (mobile, desktop, server, and more), Dart Native includes both a Dart VM with JIT (just-in-time) compilation and an AOT (ahead-of-time) compiler for producing machine code.

  • Dart Web: For programs targeting the web, Dart Web includes both a development time compiler (dartdevc) and a production time compiler (dart2js).

Dart platforms illustration

License & patents

Dart is free and open source.

See LICENSE and PATENT_GRANT.

Using Dart

Visit dart.dev to learn more about the language, tools, and to find codelabs.

Browse pub.dev for more packages and libraries contributed by the community and the Dart team.

Our API reference documentation is published at api.dart.dev, based on the stable release. (We also publish docs from our beta and dev channels, as well as from the primary development branch).

Building Dart

If you want to build Dart yourself, here is a guide to getting the source, preparing your machine to build the SDK, and building.

There are more documents in our repo at docs.

Contributing to Dart

The easiest way to contribute to Dart is to file issues.

You can also contribute patches, as described in Contributing.

Roadmap

Future plans for Dart are included in the combined Dart and Flutter roadmap on the Flutter wiki.