[BUG] .value() on empty Optional

[dlasusa]

Bug description

Actual behavior

Mojo crashed and asked I submit a bug report

Expected behavior

Not sure. I'm mostly playing/testing with Mojo. Expected it would print "None" or perhaps unable to print None? Or similar?

Steps to reproduce

from collections import Optional

@value
struct NetworkInfo:
    var target: String
    var prot: String
    var opt: String
    var source: String
    var dest: String
    var service: Optional[String]

    
    fn get_service(self) -> Optional[String]:
        if self.service:
            _full_service_entry = self.service.value()
            try:
                service_list = _full_service_entry.split(' ')
                for item in service_list:
                    if item[].find('dpt:') != -1:
                        _dpt = item[].split(':')
                        if len(_dpt) >= 2:
                            return _dpt[1]
                        else:
                            return String('Unexpected _dpt len: ', len(_dpt))
                return None
            except:
                return None
        else:
            return None

def main():
    # var x = NetworkInfo('my_target', 'my_prot', 'my_opt', 'my_source', 'my_dest', String('tcp dpt:http flags:FIN,SYN,RST,ACK/SYN')) <- this works
    var x = NetworkInfo('my_target', 'my_prot', 'my_opt', 'my_source', 'my_dest', String('tcp'))
    var the_service = x.get_service()
    print(the_service.value())

Crash report

.value() on empty Optional
Please suogram arguments: /home/me/.vscode-server/data/User/globalStorage/modular-mojotools.vscode-mojo/magic-data-home/envs/max/bin/mojo run /home/me/mojo_sys_inventory/main.mojo
Stack dump withoubmit a bug report to https://github.com/modular/mojo/issues and include the crash backtrace along with all the relevant source codes.
Stack dump:
0.      Prt symbol names (ensure you have llvm-symbolizer in your PATH or set the environment var `LLVM_SYMBOLIZER_PATH` to point to it):
0  mojo      0x00005572bba4ac0b
1  mojo      0x00005572bba48a79
2  mojo      0x00005572bba4b27d
3  libc.so.6 0x00007fc90f309330
4  libc.so.6 0x00007fc8780036c0
mojo crashed!
Please file a bug report.
Illegal instruction (core dumped)

System information

Magic info:

     Magic version: 0.7.0
System
------------
       Pixi version: 0.41.3
           Platform: linux-64
   Virtual packages: __unix=0=0
                   : __linux=5.15.167.4=0
                   : __glibc=2.39=0
                   : __cuda=12.7=0
                   : __archspec=1=skylake
          Cache dir: /home/me/.cache/rattler/cache
       Auth storage: /home/me/.rattler/credentials.json
   Config locations: No config files found

Global
------------
            Bin dir: /home/me/.modular/bin
    Environment dir: /home/me/.modular/envs
       Manifest dir: /home/me/.modular/manifests/pixi-global.toml

Project
------------
               Name: mojo_sys_inventory
            Version: 0.1.0
      Manifest file: /home/me/mojo_sys_inventory/mojoproject.toml
       Last updated: 06-03-2025 20:16:00

Environments
------------
        Environment: default
           Features: default
           Channels: https://conda.modular.com/max-nightly, https://conda.modular.com/max, https://repo.prefix.dev/modular-community, conda-forge
   Dependency count: 1
       Dependencies: max
   Target platforms: linux-64

magic list max:

Package     Version               Build    Size       Kind   Source
max         25.2.0.dev2025030619  release  9.7 KiB    conda  max
max-core    25.2.0.dev2025030619  release  244.4 MiB  conda  max-core
max-python  25.2.0.dev2025030619  release  121.3 MiB  conda  max-python

[soraros]

I think this is the expected behaviour since it should abort on an empty Optional:

max/mojo/stdlib/src/collections/optional.mojo

Lines 322 to 323 in a37617b

	if not self.__bool__():
	abort(".value() on empty Optional")

It's more of an issue with using abort for error handling. But I suppose we also couldn't do much better before pattern matching.

[ematejska]

This could definitely use a better error message behavior.

[dlasusa]

Yeah, I assume the issue is that I should be checking the type/contents of the_service before calling .value() on it? I mostly reported as a bug because the error output asked me to. Happy to close this if the output is expected and appropriate, also happy to leave it open as a reminder for better messaging if that helps?

[ematejska]

Thank you, we appreciate your report. I passed it along to the engineering team for more feedback.

[illiasheshyn]

Just a heads up, there is an existing issue regarding this #3977, however it does not provide as much information.