Better way to handle invalid configuration values to show error messages

[chanseokoh]

PluginConfigurationProcessor throws many exceptions.

      throws InvalidImageReferenceException, MainClassInferenceException, InvalidAppRootException,
          IOException, InvalidWorkingDirectoryException, InvalidContainerVolumeException,
          IncompatibleBaseImageJavaVersionException, NumberFormatException,
          InvalidContainerizingModeException, InvalidFilesModificationTimeException {

Many exceptions are only for syntactically invalid config values, but not all of them. Plugin code handles these exceptions in long catch blocks. Sometimes we use HelpfulSuggestions for error messages, but sometimes not. This long blocks are being copied over three tasks (build, dockerBuild, buildTar). I honestly don't know how we can best handle this.

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    } catch (InvalidContainerizingModeException ex) {
      throw new MojoExecutionException(
          "invalid value for <containerizingMode>: " + ex.getInvalidContainerizingMode(), ex);

    } catch (InvalidWorkingDirectoryException ex) {
      throw new MojoExecutionException(
          "<container><workingDirectory> is not an absolute Unix-style path: "
              + ex.getInvalidPathValue(),
          ex);

    } catch (InvalidContainerVolumeException ex) {
      throw new MojoExecutionException(
          "<container><volumes> is not an absolute Unix-style path: " + ex.getInvalidVolume(), ex);

    } catch (InvalidFilesModificationTimeException ex) {
      throw new MojoExecutionException(
          "<container><filesModificationTime> should be an ISO 8601 date-time (see "
              + "DateTimeFormatter.ISO_DATE_TIME) or special keyword \"EPOCH_PLUS_SECOND\": "
              + ex.getInvalidFilesModificationTime(),
          ex);

    } catch (IncompatibleBaseImageJavaVersionException ex) {
      throw new MojoExecutionException(
          HelpfulSuggestions.forIncompatibleBaseImageJavaVesionForMaven(
              ex.getBaseImageMajorJavaVersion(), ex.getProjectMajorJavaVersion()),
          ex);

    } catch (InvalidImageReferenceException ex) {
      throw new MojoExecutionException(
          HelpfulSuggestions.forInvalidImageReference(ex.getInvalidReference()), ex);

    } catch (IOException | CacheDirectoryCreationException | MainClassInferenceException ex) {
      throw new MojoExecutionException(ex.getMessage(), ex);

    } catch (BuildStepsExecutionException ex) {
      throw new MojoExecutionException(ex.getMessage(), ex.getCause());
    }
  }

[TadCordle]

I've been thinking about this a bit, and I have a couple ideas:

1. Just do straightforward code reduction. catch(Exception ex) and pass ex into a method in TaskCommon/MojoCommon that checks the type and rethrows with the message we want, and if it's not a type we know, throw ex. This doesn't help with PluginConfigurationProcessor throwing so many exceptions, but it's an easy way of reducing a decent amount of duplicate code.

2. Do something like remove all these custom exception classes and put all the failures under a JibPluginException that just takes a message. Maybe we can move all the messages we'd pass to it into HelpfulSuggestions to unify things a bit better. But this might either increase the number of parameters we need to pass into HelpfulSuggestions (since maven and gradle have different terminology, parameter names, etc.), or require us to make HelpfulSuggestions an interface with a maven and gradle implementation.