lib/SymbolGraphGen is discarding PATs from declarations

[tayloraswift]

Description

lib/SymbolGraphGen appears to be losing the some Identifiable PAT substitution when printing declaration signatures. here’s an example:

public
func f(_:some Sequence<some Identifiable>)
{
}

which simply renders as

func f(_:some Sequence)

in the generated documentation. there is no indication that this API contains additional generic constraints.

"declarationFragments": [
{
    "kind": "keyword",
    "spelling": "func"
},
{
    "kind": "text",
    "spelling": " "
},
{
    "kind": "identifier",
    "spelling": "f"
},
{
    "kind": "text",
    "spelling": "("
},
{
    "kind": "externalParam",
    "spelling": "_"
},
{
    "kind": "text",
    "spelling": ": some "
},
{
    "kind": "typeIdentifier",
    "spelling": "Sequence",
    "preciseIdentifier": "s:ST"
},
{
    "kind": "text",
    "spelling": ")"
}
],

Reproduction

see above

Expected behavior

the printed signature should include the some Identifiable constraint.

Environment

$ swift --version
Swift version 5.9.1 (swift-5.9.1-RELEASE)
Target: x86_64-unknown-linux-gnu

Additional information

No response

[slavapestov]

The declaration of f() has the same semantic effect as

public func f<T, U>(_: T) where T: Sequence, T.Element == U, U: Identifiable

and the requirements should probably be encoded in the form of a generic signature; I would not expect the type of the parameter to say "Sequence" of any sort.

[tayloraswift]

why is the second type parameter needed? couldn’t it just be

func f<T>(_:T) where T:Sequence, T.Element:Identifiable

?