Implementation `valueof`

[timotheeguerin]

Implementation of design #888

Add a new keyword called valueof that can prefix a type reference to mean that valueof TypeReference should be a value type.

valueof Scalars

Add a new keyword valueof that will let us solve this problem.

Syntax

// Option 1: With parenthese
valueof(<type>)
valueof(string)

// Option 2: Keyword
valueof <type>
valueof string

Syntax	Meaning	Example
valueof(string)	A String literal	"foo"
valueof(int32)	A integer literal	123456
valueof(int8)	A integer literal(Assignable to int8)	5
valueof(boolean)	A boolean literal	true
valueof("foo" | "bar")	A String literal that match the union	"foo"

valueof Record

First part adds a way to patch the gap for literal types. This would do a similar behavior for records.
Those values could be provided with the #{} syntax.

model Role {
  id: int32;
  name: string;
}

valueof(Role) // would mean the following

// Assignable
alias A1 = #{ id: 1 , name: "read" }
alias A2 = #{ id: 2 , name: "write" }

// Not assignable
alias B1 = #{ id: 1 , name: "read", extra: "plus" }  // Extra property
alias B2 = #{ id: int32, name: "read" }              // Not a value type

Applies valueof whenever possible recursively to each of the property type

model User {
  id: int32;
  address: {
    city: string
  }
}

#{id: 2, address: {city: "Foo"}}

Conversion of value to JS

That the rules we decided with template string proposal

1. if type is unknown or TemplatedString always pass a TemplatedString even if its a string
2. if type is string convert to a string if possible or fail
3. if type is string | TemplatedString error saying to pick one

Now we have the case

4. if type is typeof string then we pass a string or fail

This mean we probably don't want 2. to convert to a string anymore. So if you have string as the param type and the passed arg is a

• string literal -> keep as it is
• string model(or derived) -> keep as it is
• template literal-> keep as it is but error if its not serializable to string?

For #3 we probably want to also fail for valueof string | TemplateLiteral

For example this would be the generated payloads

	Cadl	Ts Signature
dec foo(target, value: string)	export function $foo( context, target, value: StringLiteral | TemplateLiteral | Scalar ) {}
dec foo(target, value: valueof string)	export function $foo(context, target, value: string) {}
dec foo(target, value: TemplateLiteral)	export function $foo(context, target, value: TemplateLiteral) {}

[markcowl]

est: 13