inline if error suggests it expects a literal expression

[deusaquilus]

Minimized code

Say we make a simple macro that just returns the value true.

object Proc {
  inline def isTrue: Boolean = ${ isTrueImpl }
  def isTrueImpl(using qctx: QuoteContext) = {
    Expr(true) // even tried: Literal(Constant(true).seal.asExprOf[Boolean])
  }
}

Now if we use that with an inline if statement:

  inline def oneOf(): String = {
    inline if (isTrue)
      "foo"
    else
      "bar"
  }

Then when I run that:

oneOf()

The following error happens...

Output

[error]    |    cannot reduce inline if
[error]    |     its condition   miniquill.ListProc.isTrue
[error]    |     is not a constant value

Expectation

I think this should be more intelligent about looking at the AST and detecting if there is a constant value. I even tried making oneOf return Literal(Constant(true)) but it still did not work.

[bishabosha]

this does not work because inline if looks at the static type of the expression - if you make isTrue a transparent inline def it works

[bishabosha]

perhaps the error is misleading

[deusaquilus]

Thanks @bishabosha! The message “it needs to be a constant” conveys the correct high-level understanding, adding “(and this expects a literal type)” in parenthesis would be a good addition though.

[nicolasstucki]

Actually, it is a shame to fail on a true: Boolean. We can easily handle those cases.