Suggestion Backlog Slog, 3/6/2017

[RyanCavanaugh]

• Proposal: int types #4639 int types
• Allow attaching a comment before all non-user injected code. #13455 Allow attaching a comment before all non-user injected code.
• Exact Types #12936 Exact Types
• Distinguish declaration file and js file when the option “Keep comments in TypeScript compiler output" is turned on #11774 Distinguish declaration file and js file when the option “Keep comments in TypeScript compiler output" is turned on
• [Proposal] External Module Type #13231 [Proposal] External Module Type
• Generic decorators - could they receive some default type arguments? #2607 Generic decorators - could they receive some default type arguments?
• tsc -w should clear screen before each run #13020 tsc -w should clear screen before each run
• Allow classes to extend from values of type any #14301 Allow extends from any (Salsa)
• Should 'Partial<T>' and Readonly<T> should have their type parameters constrained to 'object'? #14249 Constraint Partial<T>/Readonly<T> to T extends object
• Unsafe type-incompatible assignments should not be allowed #14150 strictVarianceChecks flag
• Proposal: JSX.ElementType #13890 JSX.ElementType to define the type of <Tag /> expressions
• Warning when writing a generator function without any yield #13847 Enforce generator functions to contain at least one yield
• Generalize never type handling for control flow analysis based type guard #12825 Generalize handling of never for returns
• Control flow doesn't recognise undefined check #12600 Discriminated unions of non-unit-type-discriminated unions
• Operator '+' cannot be applied to types 'T' and 'T'. #12410 Allow operator + on string|number-constrained T ?

[RyanCavanaugh]

• Proposal: int types #4639 int types
  • Just not all that useful
  • ES is looking at adding int64
  • Revisit but 👎 unless we do Web Assembly
• Allow attaching a comment before all non-user injected code. #13455 Allow attaching a comment before all non-user injected code.
  • When exactly would we emit this line?
    • Always? Only when we emit a new branch ?
    • Do our helpers suffer from this?
  • Where does this happen?
    • Can you just regex the output?
  • We could use a helper instead (makeSuper(_super, this))
  • AMF
• Pure annotation in downlevel emits #13721 Pure annotation for class emit
  • Needed for accurate tree shaking
  • Somewhat odd Uglify doesn't identify this by itself?
  • Would be emitted for classes without static initializers
  • Could be implemented by an emit transform pipeline
    • But doesn't solve tsc scenarios
    • Probably OK
    • Actually this doesn't work bescause the injection has to happen between the class emit and the IIFE emit
  • Punt to uglififer to detect this pattern instead?
  • Make loaders handle this instead?
  • Daniel will try to do this for WebPack
• Exact Types #12936 Exact Types
  • Excess property checks are already pretty good
  • Which types are exact and which aren't?
    • People may disagree
  • Some APIs really are closed
  • Sidebar on all-optional interfaces
    • Ryan should implement this and stop complaining
  • What is the behavior of this for unions / intersections?
    • Intersection... makes no sense?
      • Violates basic assumptions of assignability (T & U assignable to T)
  • What does it mean to be constrained by an exact type?
  • What about instantations of exact types?
  • Danger of bug farm
  • What is the value add here?
  • What about creating automatically-disjointing unions?
  • Outcomes
    • Need specific scenarios - is this an XY problem solution?
    • We need to fix excess property checking when the target is a union type
• tsc -w should clear screen before each run #13020 tsc -w should clear screen before each run
  • Universal acclaim in the room for this behavior
  • 👍
  • Sidenote: Accept PR to get rid of WScript host
• Allow classes to extend from values of type any #14301 Allow extends from any (Salsa)
  • 👍
  • When this happens, add a [s: string]: any signature to the type
• Should 'Partial<T>' and Readonly<T> should have their type parameters constrained to 'object'? #14249 Constrain Partial<T>/Readonly<T> to T extends object
  • For shallow variants only
  • Breaking change...
  • 👎 Annoying as hell and delivers no value
• Unsafe type-incompatible assignments should not be allowed #14150 strictVarianceChecks flag
  • Highly infectious
    • Could anyone actually get this to work?
    • You actually can't do this without the entire set of C++-like const constructs
  • Keep tabs on this
• Generalize never type handling for control flow analysis based type guard #12825 Generalize handling of never for returns
  • The control flow graph is formed during binding, but we don't have type data yet
  • We could store all calls at each flow control point and then check them for never returns and check this info for computing types
    • Expensive!
  • Correct analysis would require multiple iterations
  • Possible solutions?
    • At bind-time
      • Detect explicit : never functions
        • Or do this at parse time?
      • Store potential calls to these
    • Use this to set up a "better" flow control graph
    • Above doesn't really work due to imported identifiers...
  • No clear answers in sight

Cut for time

• Proposal: JSX.ElementType #13890 JSX.ElementType to define the type of <Tag /> expressions
• Warning when writing a generator function without any yield #13847 Enforce generator functions to contain at least one yield
• Control flow doesn't recognise undefined check #12600 Discriminated unions of non-unit-type-discriminated unions
• Operator '+' cannot be applied to types 'T' and 'T'. #12410 Allow operator + on string|number-constrained T ?
• [Proposal] External Module Type #13231 [Proposal] External Module Type
• Generic decorators - could they receive some default type arguments? #2607 Generic decorators - could they receive some default type arguments?
• Distinguish declaration file and js file when the option “Keep comments in TypeScript compiler output" is turned on #11774 Distinguish declaration file and js file when the option “Keep comments in TypeScript compiler output" is turned on