"Could not find TASTY file" error when tasty/class files already exist

[griggt]

Compiler version

3.0.0-RC1 and 3.0.0-RC2-bin-SNAPSHOT-git-086d1a8
(no issue with 3.0.0-M3)

Minimized code

// hello.scala
@main def hello = println("hello, world")

Output

$ ls -l
total 4
-rw-r--r-- 1 tgrigg tgrigg 43 Mar  7 15:34 hello.scala

$ scalac -version
Scala compiler version 3.0.0-RC1 -- Copyright 2002-2021, LAMP/EPFL

$ scalac hello.scala

$ ls -l
total 24
-rw-r--r-- 1 tgrigg tgrigg 757 Mar  7 15:35 'hello$package$.class'
-rw-r--r-- 1 tgrigg tgrigg 267 Mar  7 15:35 'hello$package.class'
-rw-r--r-- 1 tgrigg tgrigg 554 Mar  7 15:35 'hello$package.tasty'
-rw-r--r-- 1 tgrigg tgrigg 882 Mar  7 15:35  hello.class
-rw-r--r-- 1 tgrigg tgrigg  43 Mar  7 15:34  hello.scala
-rw-r--r-- 1 tgrigg tgrigg 471 Mar  7 15:35  hello.tasty

$ scalac hello.scala
Could not find TASTY file hello.tasty under ./hello.class
1 error found

Expectation

No error

Notes

Seems to only be a problem when the class/tasty files are in the current directory.

[griggt]

This issue appeared recently after #11308 was merged, but what looks to be the root cause is much older (since #3382): dotty.tools.io.Path#parent appears to be broken for files in the current directory.

https://github.com/lampepfl/dotty/blob/086d1a852a1412fb21124b5afdb1022c6d278d8b/compiler/src/dotty/tools/io/Path.scala#L126-L132

sbt:scala3> console

scala> import dotty.tools.io._

scala> Path("./foo.txt").parent
val res0: dotty.tools.io.Directory = ./foo.txt

scala> Path("foo.txt").parent                                                                                         
val res1: dotty.tools.io.Directory = foo.txt

scala> Path("/foo.txt").parent
val res2: dotty.tools.io.Directory = /

scala> Path("./bar/foo.txt").parent                                                                                     
val res3: dotty.tools.io.Directory = bar

scala> Path(".").parent
val res4: dotty.tools.io.Directory = .

Compare Scala 2.13:

sbt:root> console
[info] Starting scala interpreter...
Welcome to Scala 2.13.5 (OpenJDK 64-Bit Server VM, Java 1.8.0_282).
Type in expressions for evaluation. Or try :help.

scala> import scala.reflect.io._
import scala.reflect.io._

scala> Path("./foo.txt").parent
val res0: scala.reflect.io.Directory = .

scala> Path("foo.txt").parent
val res1: scala.reflect.io.Directory = .

scala> Path("/foo.txt").parent
val res2: scala.reflect.io.Directory = /

scala> Path("./bar/foo.txt").parent
val res3: scala.reflect.io.Directory = ./bar

scala> Path(".").parent
val res4: scala.reflect.io.Directory = ..

The Scala 2.13 implementation is here: https://github.com/scala/scala/blob/262f6e9a6d217a8c95dd6e70235f0c615edd50e6/src/reflect/scala/reflect/io/Path.scala#L155-L171

[odersky]

@bishabosha @nicolasstucki maybe one of you could take a look?