Compiler assertion error when assigning variable using error

[jasoncarr0]

This function body causes an assertion error in the compiler (version 0.42.0 in this case but I also see it in a slightly modified version of 0.45.0). I couldn't find another issue for this yet but it's not easy to search for.

Found this on a hunch/check while looking at the error-flag code, hoping to fix with possible other changes

     let x: String = (error)

This results in:

[removed]/ponyc/src/libponyc/pass/expr.c:652: pass_expr: Assertion `errors_get_count(options->check.errors) > 0` failed.

Backtrace:
  ./build/debug/ponyc(ponyint_assert_fail+0x96) [0x85e4b6]
  ./build/debug/ponyc(pass_expr+0x51d) [0x7bbfcd]
  ./build/debug/ponyc(ast_visit+0x2a4) [0x7bc904]
  ./build/debug/ponyc(ast_visit+0x1e4) [0x7bc844]
  ./build/debug/ponyc(ast_visit+0x1e4) [0x7bc844]
  ./build/debug/ponyc(ast_visit+0x1e4) [0x7bc844]
  ./build/debug/ponyc(ast_visit+0x1e4) [0x7bc844]
  ./build/debug/ponyc(ast_visit+0x1e4) [0x7bc844]
  ./build/debug/ponyc(ast_visit+0x1e4) [0x7bc844]
  ./build/debug/ponyc(ast_visit+0x1e4) [0x7bc844]
  ./build/debug/ponyc() [0x7bd366]
  ./build/debug/ponyc() [0x7bcd8a]
  ./build/debug/ponyc(ast_passes_program+0x22) [0x7bc9d2]
  ./build/debug/ponyc(program_load+0xb8) [0x7df0e8]
  ./build/debug/ponyc() [0x76538c]
  ./build/debug/ponyc(main+0x261) [0x765241]
  /usr/lib/libc.so.6(__libc_start_main+0xd0) [0x7f1ffd34e780]
  ./build/debug/ponyc(_start+0x2a) [0x764f1a]

In addition, there seems to be a parse error if (error) is replaced by error,
as in let x: String = error

[mikumikudice]

Investigating I found that the error occurs when is_typecheck_error returns true, while switching ast_id(ast). I don't know how the compiler actually works but I presume that when the function returns true without rising an error within the if block the crash happens. I also presume that matching as an expression and not an assignment is the reason that let x: String = error doesn't cause a crash too.

[jemc]

Thanks for looking into it!

I think we should add to that line you linked so that we not only return false, but also add a compilation error like this:

    ast_error(opt->check.errors, ast,
      "right side must be something that can be assigned");

[ergl]

In addition, there seems to be a parse error if (error) is replaced by error, as in let x: String = error

Should this be made into its own issue? The original error existed for other non-assignable expressions such as let x: String = (return), which should continue to be a parse error even when removing the parenthesis.