Suggestion Backlog Slog, 9/13/2017

[RyanCavanaugh]

• Surprising Not all code paths return a value #18319 Perhaps-unexpected implicit return error is bad?
• allow typeof expressions in extends and implements list #18271 Allow typeof in extends / implements clauses
• Cannot implement generic type guarding function #18202 Make type guards be an inference position
• Merging constants with namespaces #18163 Merge value namespaces with other values
• Discriminated Unions don't cast with single type #18056 Single-case discriminated unions don't produce never
• Need way to express hybrid types that are indexable for a subset of properties  #17867 "Fallback" index signatures for non-declared properties only
• Can we define a ReadOnly interface directly? #17769 readonly declaration modifier for interfaces
• Star-imported module should conform to the type of a string-indexed object #17622 Module object imports should be able to implicitly satisfy index signatures
• Extending string-based enums #17592 Extending an existing string enum
• Infer extra parameter types from default values #17559 Issue an implicit any warning on an implicit-any parameter
• SUGGESTION: enable forceConsistentCasingInFileNames by default #17542 Turn on consistent filename enforcement by default
• Add simulated nominal type for COM SAFEARRAY and VarDate to lib.scripthost.d.ts #17526 Add psuedonominal type for VarDate and COM SAFEARRAY in lib.scripthost.d.ts
• Recursive generics in function parameters are inferred as {}, and produce funky Intellisense #17522 Recursive generic constraint produce unexpected {}
• Support inferred string-modified union types #17512 Support inferring types of concatenation of string constants/unions
• Allow calls to overloaded functions when all possible combinations of union type parameters resolve to valid overloads #17471 Something about generic overloads
• Suggestion: CFA, assignment, strict null checks and function scope #17449 Better CFA when a variable is definitely initialized (and stays initialized)
• Typescript forbids safety checks that check equality of values with different generic types #17445 Allow comparison of any two type variables
• Support non-null assertion for destructuring #17390 Support non-null assertion somewhere in the destructuring syntax
• Arrow function is not compatible with ordinary one #17113 Overriding prototype method with arrow function should be allowed

[RyanCavanaugh]

• Surprising Not all code paths return a value #18319 Perhaps-unexpected implicit return error is bad?
  • Consistency of contextual return type vs predictability of when this should happen
  • 👍
• allow typeof expressions in extends and implements list #18271 Allow typeof in extends / implements clauses
  • For extends this is bad
  • For implements this is doable with parser changes
  • Concerns about parsing
  • 👎 Write a type alias
• Cannot implement generic type guarding function #18202 Make type guards be an inference position
  • 👍
• Merging constants with namespaces #18163 Merge value namespaces with other values
  • We can't emit the var statement in this case
  • Does this merge with the variable or the type?
    • The variable: Now the declared type isn't the actual type?
    • The type: Now you're changing random other types, maybe accidently?
  • 👎 Demonstrate how to type this library using existing mechanisms
• Discriminated Unions don't cast with single type #18056 Single-case discriminated unions don't produce never
  • Now we'd be doing CFA for all types? Or just those containing unit types?
    • Currently CFA only applies to union types
  • Workaround is good enough
  • 👎
• Need way to express hybrid types that are indexable for a subset of properties  #17867 "Fallback" index signatures for non-declared properties only
  • You can use intersection types to work around this behavior
    • Except not really
  • [...]: string ?
  • AMF, esp. use cases from DT
• Star-imported module should conform to the type of a string-indexed object #17622 Module object imports should be able to implicitly satisfy index signatures
  • 👍 check if the originating symbol for the declared type is an import *; or try setting the same flag on import *s as object literals
• Extending string-based enums #17592 Extending an existing string enum
  • Dan's wanted it forever
  • Currently these types are distinct and the derived type will not be compatible with the base type
  • Nice idea but not a big demand for it yet
  • Some pretty good workarounds exist
  • AMF
• Infer extra parameter types from default values #17559 Issue an implicit any warning on an implicit-any parameter
  • Every falseandtru bug starts with a riddle :laugh:
  • How did this code get written...?
  • 👍 Try not providing a contextual type if the arity count is wrong
• SUGGESTION: enable forceConsistentCasingInFileNames by default #17542 Turn on consistent filename enforcement by default
  • Breaking change that annoys Windows people
    • But random breaks from this being off are breaking tools even on Windows
  • This is the Right Thing to Do (tm)
  • Wailing and gnashing of teeth from VS users
  • Rathole on tsc --init
  • 👍 👎 on for tsc --init but off by default
• Add simulated nominal type for COM SAFEARRAY and VarDate to lib.scripthost.d.ts #17526 Add psuedonominal type for VarDate and COM SAFEARRAY in lib.scripthost.d.ts
  • 👍 Accepting PRs
• Recursive generics in function parameters are inferred as {}, and produce funky Intellisense #17522 Recursive generic constraint produce unexpected {}
  • Super unclear how we would get this to work
• Support inferred string-modified union types #17512 Support inferring types of concatenation of string constants/unions
  • Concern about combinatorial explosion of types
  • Without a way to quickly declare the output types, there's not much use
• Suggestion: CFA, assignment, strict null checks and function scope #17449 Better CFA when a variable is definitely initialized (and stays initialized)
  • We don't have the extra pass necessary to detect that there are no further assignments
  • Use const per usual
  • Deferred until there would be a more positive set of outcomes from adding an additional pass
• Typescript forbids safety checks that check equality of values with different generic types #17445 Allow comparison of any two type variables
  • Sound, but wat
    • Technically any === operation is sound but that doesn't make it a good idea
  • 👎

Bonus slog: How to ban [1, 2, 3].sort() ?