When writing the following code:

  var x = switch (foo) { case A, B -> "x"; };

I expect there to be a compiler error because foo is not defined as a variable. In jshell, I'm getting quite a few error messages:

  jshell> var x = switch (foo) { case A, B -> "x"; };
  | Error:
  | cannot find symbol
  | symbol: variable foo
  | var x = switch (foo) { case A, B -> "x"; };
  | ^-^
  | Error:
  | illegal parenthesized expression
  | var x = switch (foo) { case A, B -> "x"; };
  | ^---^
  | Error:
  | cannot find symbol
  | symbol: variable A
  | var x = switch (foo) { case A, B -> "x"; };
  | ^
  | Error:
  | cannot find symbol
  | symbol: variable B
  | var x = switch (foo) { case A, B -> "x"; };
  | ^
  | Error:
  | the switch expression does not cover all possible input values
  | var x = switch (foo) { case A, B -> "x"; };
  | ^--------------------------------^

The last error message about not covering all possible input values is a bit confusing, as it seems to be premature. I don't get that error when using javac directly on:

  class Foo {
    public static void main(String[] args) {
      var x = switch (foo) { case A, B -> "x"; };
    }
  }

Instead, I'm getting:

  C:\Users\lukas>"\Program Files\Java\jdk-12.0.1\bin\javac.exe" --enable- preview --release 12 Foo.java
  Foo.java:3: error: cannot find symbol
      var x = switch (foo) { case A, B -> "x"; };
                      ^
    symbol: variable foo
    location: class Foo
  Foo.java:3: error: illegal parenthesized expression
      var x = switch (foo) { case A, B -> "x"; };
                     ^
  Foo.java:3: error: cannot find symbol
      var x = switch (foo) { case A, B -> "x"; };
                                  ^
    symbol: variable A
    location: class Foo
  Foo.java:3: error: cannot find symbol
      var x = switch (foo) { case A, B -> "x"; };
                                   ^
    symbol: variable B
    location: class Foo
  Note: Foo.java uses preview language features.
  Note: Recompile with -Xlint:preview for details.
  4 errors

I suggest removing the premature error message in jshell