Patterns flow analysis: recognize trivially exhaustive switches.

This fixes a minor bug in flow analysis which was preventing it from
recognizing when a switch statement was trivially exhaustive, meaning
one of its reachable cases was guaranteed to always match.

This mostly addresses
https://github.com/dart-lang/language/issues/2980, but flow analysis
still fails to recognize that:

- A list pattern containing a just a single rest pattern always
  matches (unless the rest pattern has a subpattern that may fail to
  match).

- A null check pattern always matches if its subpattern always matches
  and the matched value type is non-nullable.

- The relational pattern `!= null` always matches if its subpattern
  always matches and the matched value type is non-nullable.

Fortunately, these drawbacks are small and don't lead to unsoundness.
I'll try to address them in follow up CLs.

Bug: https://github.com/dart-lang/language/issues/2980
Change-Id: Ie9f8564cde66a5a2c41114033ca3ff0e1a0f139a
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/293860
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Commit-Queue: Paul Berry <paulberry@google.com>
Reviewed-by: Johnni Winther <johnniwinther@google.com>
4 files changed
tree: 09756559709675362bfd90888bcf16a85cd125cf
  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. .vpython
  22. AUTHORS
  23. BUILD.gn
  24. CHANGELOG.md
  25. codereview.settings
  26. CONTRIBUTING.md
  27. DEPS
  28. LICENSE
  29. OWNERS
  30. PATENT_GRANT
  31. PRESUBMIT.py
  32. README.dart-sdk
  33. README.md
  34. sdk_args.gni
  35. SECURITY.md
  36. WATCHLISTS
README.md

Dart

A client-optimized language for fast apps on any platform

Dart is:

  • Optimized for UI: Develop with a programming language specialized around the needs of user interface creation.

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

  • Fast on all platforms: Compile to ARM & x64 machine code for mobile, desktop, and backend. Or compile to JavaScript for the web.

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

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There are more documents on our wiki.

Contributing to Dart

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

You can also contribute patches, as described in Contributing.