make getTargetType return undefined if would return self

Describe the bug

Version: 9.1.0

To Reproduce

import dedent from 'dedent'
import * as tsm from 'ts-morph'
import { dumpType } from './utils'

const tsMorphProject = new tsm.Project({
  skipAddingFilesFromTsConfig: true,
  useInMemoryFileSystem: true,
})

tsMorphProject.createSourceFile(
  '/repro-example.ts',
  dedent`
    export interface Foo<T> {}
  `
)

tsMorphProject.addSourceFileAtPath('/repro-example.ts')

tsMorphProject.getSourceFiles().map((sf) => {
  sf.getExportedDeclarations().forEach((ex) => {
    const t = ex[0]!.getType()!
    dumpType(t)
  })
})

My log:

t.getText()                                          = import("/repro-example").Foo<T>
t.getSymbol()?.getName()                             = Foo
t.compilerType.getFlags()                            = 524288
(t.compilerType as tsm.ts.ObjectType)?.objectFlags   = 6
t.getAliasSymbol()?.getName()                        = undefined
t.getApparentType().getText()                        = import("/repro-example").Foo<T>
t.getSymbol()?.getDeclarations()?.[0]?.getKindName() = InterfaceDeclaration
t.getSymbol()?.getDeclarations()?.[0]?.getText()     = export interface Foo<T> {}

t.isAnonymous()                                      = false
t.isAny()                                            = false
t.isInterface()                                      = true
t.isObject()                                         = true
t.isArray()                                          = false
t.isBoolean()                                        = false
t.isBooleanLiteral()                                 = false
t.isClass()                                          = false
t.isClassOrInterface()                               = true
t.isEnum()                                           = false

t.getAliasTypeArguments().length}                    = 0
Boolean(t.getTargetType())                           = true
t.getTargetType() === t                              = true

t.getText(undefined, tsm.ts.TypeFormatFlags.InTypeAlias)                           = Foo<T>
t.getText(undefined, tsm.ts.TypeFormatFlags.UseAliasDefinedOutsideCurrentScope)    = Foo<T>
t.getText(undefined, tsm.ts.TypeFormatFlags.UseTypeOfFunction)                     = Foo<T>
t.getText(undefined, tsm.ts.TypeFormatFlags.UseFullyQualifiedType)                 = import("/repro-example").Foo<T>
t.getText(undefined, tsm.ts.TypeFormatFlags.NoTruncation)                          = Foo<T>
t.getText(undefined, tsm.ts.TypeFormatFlags.UseStructuralFallback)                 = Foo<T>

Target Type?
------------
N/A

Notice that I mark Foo has having no target type here (N/A) because the target type refers to self via reference equality.

Expected behavior

This looks like a bug to me. It seems that calling getTargetType in this case should return undefined (or maybe slightly better null). It seems to me that getTargetType should recursively return values until the terminal non-instantiated type-with-generics is reached.

[dsherret]

@jasonkuhrt sure! Yeah, on the JS doc just saying it will return itself if it’s already the target type.

[jasonkuhrt]

Ok understood, maybe we can mention this on the docs or something. Would you be open for a PR for that?