TypeChecker returns incorrect flags & types on boolean type

[fis-cz]

TypeScript Version: 2.2.1

While using the API & TypeChecker I have noticed strange behavior for boolean type in AST tree (see bellow). Is it correct? If so, is there a simple way how to reconstruct the original TypeScript code form AST with the boolean type instead of union type?

Code

Code used in test file:

function(): boolean { return false; }
function(): true | false { return false; }
function(): string | boolean { return "" }

Code using API:

let program: ts.Program = ts.createProgram(...);
let checker: ts.TypeChecker = program.getTypeChecker();
...
ts.forEachChild(node, (n: ts.Node) => {
   ...
   let t: ts.Type = checker.getTypeAtLocation(n.type);
   ...
}

Expected behavior:
for boolean:

t: ts.Type === {
   ...
   flags: TypeFlags.Boolean
   types: undefined
   ...
}

for: true | false

t: ts.Type === {
   ...
   flags: TypeFlags.Boolean | TypeFlags.Union
   types: [ { ... false ...}, { ... true ... } ]
   ...
}

for: string | boolean

t: ts.Type === {
   ...
   flags: TypeFlags.Union
   types: [ { ... string ...}, { ... boolean ... } ]
   ...
}

Actual behavior:
for: boolean (Incorrect)

t: ts.Type = {
   ...
   flags TypeFlags.Boolean | TypeFlags.Union
   types: [ { ... false ... }, { ... true ... } ]
   ...
}

for: true | false (Correct)

t: ts.Type = {
   ...
   flags: TypeFlags.Boolean | TypeFlags.Union
   types: [ { ... false ... }, { ... true ... } ]
   ...
}

for: string | boolean (Incorrect)

t: ts.Type = {
   ...
   flags: TypeFlags.Union
   types: [ { ... string ...}, { ... true ... }, { ... false ... } ]
   ...
}

[ahejlsberg]

The actual behavior you're seeing is intended. There is no difference between boolean, false | true, and true | false, they're just different ways of referencing the exact same type. In fact, boolean is effectively just a predefined type alias for false | true.

[ahejlsberg]

And, to answer your second question, there is no way to get back to the original AST representation from a type object.

[fis-cz]

Thanks for answer. A was afraid of it :) Actually, there is one way, but not ideal - it is .getText() of symbol which returns the text from the source file (parsed token).