[Bug c++/108205] New: ICE following "unused parameter" in precondition

[webrown.cpp at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108205

            Bug ID: 108205
           Summary: ICE following "unused parameter" in precondition
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: webrown.cpp at gmail dot com
  Target Milestone: ---

Using (Homebrew GCC HEAD-37c2d99) 13.0.0 20221213 (experimental)
and compiling via:
  g++-HEAD -std=c++23 -fmodules-ts -fcontracts -pedantic-errors \
    -O0 -Wall -Wextra -Werror -Wpedantic \
    -fno-builtin -fconcepts-diagnostics-depth=2
on an x86 MacBook Pro.

This code compiles:

[[nodiscard]] constexpr int
  quotient( double x, double y ) noexcept
{
  [[assume (y != 0.0)]];
  return int(x / y);
}

The same code also compiles as a module:

export module test;
export [[nodiscard]] constexpr int
  quotient( double x, double y ) noexcept
{
  [[assume (y != 0.0)]];
  return int(x / y);
}

But reformulating the assumption as a precondition causes issues.
First, this code is diagnosed with "unused parameter 'x'", which
seems misleading:

[[nodiscard]] constexpr int
  quotient( double x, double y ) noexcept
  [[ pre: y != 0.0 ]]
{
  return int(x / y);
}

Second, when the above is compiled as a module, the compiler 
additionally segfaults:

export module test;
export [[nodiscard]] constexpr int
  quotient( double x, double y ) noexcept
  [[ pre: y != 0.0 ]]
{
  return int(x / y);
}