String interpolation followed by a dot is missing string literals

[tgodzik]

Compiler version

3.2.0-RC1

Minimized code

object Main {
 s"Hello $Main.toStr!"
}

Output

This is the tree representing the string interpolation:

 Select(
    qualifier = Apply(
      fun = Select(
        qualifier = Apply(
          fun = Select(
            qualifier = Select(
              qualifier = Select(qualifier = Ident(name = _root_), name = scala),
              name = StringContext
            ),
            name = apply
          ),
          args = List(
            Typed(
              expr = SeqLiteral(
                elems = List(Literal(const = ( = "Hello "))),
                elemtpt = ...
              ),
              tpt = ...
            )
          )
        ),
        name = s
      ),
      args = List(
        ...
      )
    ),
    name = <error>
  ),

Notice it only contains "Hello " literal.

Expectation

 Select(
    qualifier = Apply(
      fun = Select(
        qualifier = Apply(
          fun = Select(
            qualifier = Select(
              qualifier = Select(qualifier = Ident(name = _root_), name = scala),
              name = StringContext
            ),
            name = apply
          ),
          args = List(
            Typed(
              expr = SeqLiteral(
                 elems = List(Literal(const = ( = "Hello ")), Literal(const = ( = ".toStr!")))
                elemtpt = ...
              ),
              tpt = ...
            )
          )
        ),
        name = s
      ),
      args = List(
        ...
      )
    ),
    name = <error>
  ),

The main part is elems = List(Literal(const = ( = "Hello ")), Literal(const = ( = ".toStr!")))

[som-snytt]

Remarkably,

scala> object Main { def m = s"Hello $Main.toStr!" }
// defined object Main

scala> Main.m
val res0: String = Hello rs$line$2$Main$@44ddb518.toStr!

[odersky]

I also don't see yet what is wrong here. There is no error reported and it generates the correct code.

[som-snytt]

I took a look and will follow up. The dot is tokenized FSR after self type looks ahead, maybe something to do with string interpolation as two tokens, the part and the embedded ident.

[som-snytt]

Probably this edge case results from a tweak to lookahead #14562

My proposed fix is defensive. I'll consider whether it's possible to tweak scanning the interpolation instead.

[odersky]

I still don't understand what is wrong.

[som-snytt]

I was about to comment on the mechanics, which were challenging enough that I hadn't taken a global view yet.

Calling lookahead at INTERPOLATIONID populates current token at STRINGPART and next at IDENT, but reset makes current INTERPOLATIONID and next at STRINGPART, so IDENT is dropped. getNextToken winds up with last STRINGPART, so when it sees the dot it takes it as DOT. Again, it's only with the interpolation in "self-type position".

It works either to avoid lookahead in that case, or resort to LookaheadScanner.

I'll look at whether producing STRINGPART can be less eager in producing the next IDENT. One idea is that if it's done in postProcess, then lookahead won't do it, much like fusion of case class.

[odersky]

I mean globally rather than the mechanics. It does produce produce the correct string, no?

[som-snytt]

It looks like I edited my previous comment. I'll show the spurious syntax error in a minute after a recompile. Maybe a couple of minutes.

I was about to go read some early morning headlines.

The unexpected token is DOT. Sorry, Dotty.

[success] Total time: 190 s (03:10), completed Jun 24, 2022, 5:18:21 AM
Welcome to Scala 3.2.1-RC1-bin-SNAPSHOT-git-327ecc2 (17.0.2, Java OpenJDK 64-Bit Server VM).
Type in expressions for evaluation. Or try :help.

scala> object Main { s"Hello $Main.toStr!" }
-- [E016] Syntax Error: ------------------------------------------------------------------------------------------------
1 |object Main { s"Hello $Main.toStr!" }
  |                           ^
  |                           Error in interpolated string: identifier or block expected
  |
  | longer explanation available when compiling with `-explain`
-- [E040] Syntax Error: ------------------------------------------------------------------------------------------------
1 |object Main { s"Hello $Main.toStr!" }
  |                            ^
  |                            an identifier expected, but string literal found

scala>

[odersky]

Ah, now I get it. I tried with normal console but that was still 3.1.3.