Class properties doesn't inherit types from interface

[alexdima]

Moved from microsoft/vscode#2881
From @moostad

[DanielRosenwasser]

#6118 should fix this, right @sandersn?

[sandersn]

No, #6118 only fixes contextual typing of implemented properties. The fix is probably related, but they are two separate bugs.

[RyanCavanaugh]

Raw notes

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Where did it come from: base class or implemented interface
Is it: Initializer, property declaration, method declaration, or constructor declaration

• Initializers of property declarations without type annotations
  • Contextually type from base class if it exists
  • Contextually type from implemented interfaces if all declarations have identical types
  • Otherwise none
• Method declarations
  • Return expressions get contextually typed by base signature's return type
  • Unannotated parameters get contextually typed by base signature's parameter types
• Unannotated uninitialized declarations
  • Simply get base type's type
  • foo; is as if you had written foo = undefined;, e.g. get foo: string if that was your base type's foo
• Same for static declarations and constructor parameters

[xzilja]

This still seems to be an issue, any development on it? Feels trivial to re-type everything that is already defined in implemented interface

[sandersn]

We re-discuss it every six months or so, and haven't come up with any new ways to fix it without breaking old code.

[robertdempsey]

@sandersn do you mean breaking old code that's out in the world that's not conforming to interfaces being implemented?

[sandersn]

@robertdempsey See this comment in #6118 for details under the heading "The ugly". The code there is arguably correct, or at least useful, as-is.

[RyanCavanaugh]

Tracking at #10570 now

[typescript-bot]

Automatically closing this issue for housekeeping purposes. The issue labels indicate that it is unactionable at the moment or has already been addressed.