(lib/SymbolGraphGen) incorrect parsing of concrete Self type tokens in function signatures

[tayloraswift]

Description

given some input signatures like these:

public
struct Struct
{
    public
    func combined(with other:Self) -> Self
    {
        self
    }
    public
    func combined(with other:Int) -> Int
    {
        0
    }
}

lib/SymbolGraphGen will not parse the former correctly, it will instead dump something like this:

"declarationFragments":[{"kind":"keyword","spelling":"func"},{"kind":"text","spelling":" "},{"kind":"identifier","spelling":"combined"},{"kind":"text","spelling":"("},{"kind":"externalParam","spelling":"with"},{"kind":"text","spelling":" "},{"kind":"internalParam","spelling":"other"},{"kind":"text","spelling":": `Self`"},{"kind":"text","spelling":") -> "},{"kind":"typeIdentifier","spelling":"Struct","preciseIdentifier":"s:10Signatures6StructV"}]

which contains a garbage ': `Self`' token.

for some reason, the return type is correctly detected and canonicalized from Self to Struct.

this only affects non-generic Self, truly generic Self does not appear to be affected.

Reproduction

see above

Expected behavior

there should be a text token containing ': ' and a typeIdentifier token containing Struct.

Environment

$ swift --version
Swift version 6.0.2 (swift-6.0.2-RELEASE)
Target: x86_64-unknown-linux-gnu

Additional information

No response

[tayloraswift]

i did some more investigation, and it appears this behavior is inconsistent between symbol graphs generated via -Xswiftc -emit-symbol-graph and swift symbolgraph-extract.

for some reason, symbol graphs generated via the latter do not exhibit this issue, only symbol graphs generated via -emit-symbol-graph?