TypeError: object caps does not have a member type Cap

[GoogeTan]

Compiler version

Scala 3.4.2

Minimized code

https://github.com/GoogeTan/DottyCrashExample
I have tried to make it as small as possible. If last commit doesn't crash on your pc then try previous one.

Output (click arrow to expand)

scala: compiling 1 Scala source to D:\DottyCrashExample\layout\target\scala-3.4.2\classes ...
scala: 
  unhandled exception while running MegaPhase{protectedAccessors, extmethods, uncacheGivenAliases, checkStatic, elimByName, hoistSuperArgs, forwardDepChecks, specializeApplyMethods, tryCatchPatterns, patternMatcher} on D:\DottyCrashExample\layout\src\main\scala\DP.scala

  An unhandled exception was thrown in the compiler.
  Please file a crash report here:
  https://github.com/scala/scala3/issues/new/choose
  For non-enriched exceptions, compile with -Yno-enrich-error-messages.

     while compiling: D:\DottyCrashExample\layout\src\main\scala\DP.scala
        during phase: MegaPhase{protectedAccessors, extmethods, uncacheGivenAliases, checkStatic, elimByName, hoistSuperArgs, forwardDepChecks, specializeApplyMethods, tryCatchPatterns, patternMatcher}
                mode: Mode(ImplicitsEnabled)
     library version: version 2.13.12
    compiler version: version 3.4.2
            settings: -classpath D:\DottyCrashExample\layout\target\scala-3.4.2\classes;D:\DottyCrashExample\common\target\scala-3.4.2\classes;C:\Users\Googl\AppData\Local\Coursier\cache\v1\https\repo1.maven.org\maven2\org\scala-lang\scala-library\2.13.10\scala-library-2.13.10.jar;C:\Users\Googl\AppData\Local\Coursier\cache\v1\https\repo1.maven.org\maven2\org\scala-lang\scala3-library_3\3.3.1\scala3-library_3-3.3.1.jar;C:\Users\Googl\AppData\Local\Coursier\cache\v1\https\repo1.maven.org\maven2\org\typelevel\cats-core_3\2.10.0\cats-core_3-2.10.0.jar;C:\Users\Googl\AppData\Local\Coursier\cache\v1\https\repo1.maven.org\maven2\org\typelevel\cats-kernel_3\2.10.0\cats-kernel_3-2.10.0.jar;C:\Users\Googl\AppData\Local\Coursier\cache\v1\https\repo1.maven.org\maven2\org\typelevel\cats-mtl_3\1.4.0\cats-mtl_3-1.4.0.jar -d D:\DottyCrashExample\layout\target\scala-3.4.2\classes

scala: ## Exception when compiling 1 sources to D:\DottyCrashExample\layout\target\scala-3.4.2\classes
dotty.tools.dotc.core.TypeError$$anon$1: object caps does not have a member type Cap

           
scala: Compilation failed when compiling to: D:\DottyCrashExample\layout\target\scala-3.4.2\classes
  object caps does not have a member type Cap

[som-snytt]

The build.sbt should say

libraryDependencies ++= defaultLibraries

instead of :=.

It is annoying that we must suffer typos the hard way.

Edit: without the jar dependency, that is, setting dependencies to nil, you get the friendlier:

[error] Could not find package scala from compiler core libraries.
[error] Make sure the compiler core libraries are on the classpath.
[error]
[error] (layout / Compile / compileIncremental) Compilation failed

[WojciechMazur]

The cause of this cryptic error can be fixed using #20493