[Bug c++/89785] New: Incorrect "not a constant expression" error with switch statement that returns

[antoshkka at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89785

            Bug ID: 89785
           Summary: Incorrect "not a constant expression" error with
                    switch statement that returns
           Product: gcc
           Version: 9.0
            Status: UNCONFIRMED
          Keywords: rejects-valid
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: antoshkka at gmail dot com
  Target Milestone: ---

The following code fails to compile:

constexpr int Addrlen(int domain) {
    switch (domain) {
      case 0:
        return 0;
      case 2:
        return 42;
    }
    throw 42;
}

Error message is following:

<source>: In function 'constexpr int Addrlen(int)':
<source>:8:11: error: expression '<throw-expression>' is not a constant
expression
    8 |     throw 42;
      |           ^~