- [x] Have you followed the [guidelines for contributing](https://github.com/snapcore/snapcraft/blob/master/CONTRIBUTING.md)? - [x] Have you signed the [CLA](http://www.ubuntu.com/legal/contributors/)? - [x] If this is a bugfix. Have you checked that there is a bug report open for the issue you are trying to fix on [bug reports](https://bugs.launchpad.net/snapcraft)? - [x] If this is a new feature. Have you discussed the design on the [forum](https://forum.snapcraft.io)? - [x] Have you successfully run `./runtests.sh static`? - [x] Have you successfully run `./runtests.sh unit`? ----- This PR modifies `repo._deb` to handle failure to `sudo apt-get install` new packages as [reported in the forum](https://forum.snapcraft.io/t/unable-to-correct-problems-you-have-held-broken-packages/4584). Typically this occurs when packages have conflicting dependencies. Currently Snapcraft just bails out with a stack trace in this case. The Python Apt bindings have a heuristic that's similar to what `apt-get` does but exposes less information. So if it fails to resolve conflicts in `apt.Package.mark_install` we get a `SystemError` with not enough details to produce a sensible error message. By specifying `auto_fix=False` we can always fall-through to `apt-get` which will show a verbose error message so just referring to the packages we couldn't install is still clear enough even if we don't know which one(s) specifically failed. For this case I'm introducing a new `BuildPackagesNotInstalledError`. The following new tests are being added: - tests.unit.repo.test_deb.test_broken_package_apt_install - To verify that `apt-get install` failing with a `CalledProcessError` is handled. I locally ran the tests: - `./runtests.sh tests/unit` with unrelated failures in [tests.unit.test_lifecycle.CoreSetupTestCase.test_core_setup_if_docker_env](https://bugs.launchpad.net/snapcraft/+bug/1752576), `tests.unit.test_mangling.TestClearExecstack.test_execstack_clears` and `tests.unit.test_elf`. - `./runtests.sh tests/integration` with one unrelated failure in [tests.integration.general.test_parser.TestParserWikis](https://bugs.launchpad.net/snapcraft/+bug/1752580) - `./runtests.sh static`: Everything passed Manual test steps: - cd tests/integration/snaps/basic - Add this line to `snap/snapcraft.yaml`: `build-packages: [cpp-arm-linux-gnueabihf, gcc-5-arm-linux-gnueabihf, gcc-arm-linux-gnueabihf, gcc-multilib]` - snapcraft - Observe that you get an error that looks like this: `The following packages have unmet dependencies:` ` gcc-5-arm-linux-gnueabihf : Conflicts: gcc-multilib but 4:5.3.1-1ubuntu1 is to be installed` ` gcc-multilib : Conflicts: gcc-5-arm-linux-gnueabihf` ` Conflicts: gcc-5-arm-linux-gnueabihf:i386` `Could not install all requested build packages: gcc-5-arm-linux-gnueabihf gcc-arm-linux-gnueabihf gcc-multilib`