Migration: do not union inferred types in overrides.

Previously, when handling an override such as:

  abstract class A {
    int/*?*/ f();
  class C implements A {
    f() => 0;

we would create a union edge between the implicit return type of C.f
and the explicit return type of A.f.  This was a problem because
nullability information can propagate bidirectionally through union
edges, so it could result in types unnecessarily becoming nullable,

  abstract class A {
    int/*?*/ f();
  abstract class B {
    int f(); // Should not need to be made nullable
  class C implements A, B {
    f() => 0;

This CL fixes the problem by just making ordinary unidirectional edges
for overrides involving inferred types.

Change-Id: I63a5f1f640b5543fcf39304087592e984aa66694
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/141853
Commit-Queue: Paul Berry <paulberry@google.com>
Reviewed-by: Mike Fairhurst <mfairhurst@google.com>
4 files changed
tree: a5a58e3da218c7e81a674a89908e1b146889a0a1
  1. .clang-format
  2. .dart_tool/
  3. .gitattributes
  4. .gitconfig
  5. .github/
  6. .gitignore
  7. .gn
  8. .mailmap
  9. .packages
  10. .style.yapf
  11. .vpython
  13. BUILD.gn
  14. CHANGELOG.md
  16. DEPS
  19. PRESUBMIT.py
  20. README.dart-sdk
  21. README.md
  23. benchmarks/
  24. build/
  25. client/
  26. codereview.settings
  27. docs/
  28. pkg/
  29. runtime/
  30. samples-dev/
  31. samples/
  32. sdk/
  33. sdk_args.gni
  34. sdk_nnbd/
  35. tests/
  36. third_party/
  37. tools/
  38. utils/


A client-optimized language for fast apps on any platform

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