Fix bug where "use --force" prompt is not displayed

For some reason our series selector was not returning an
UnsupportedSeries error when it should have been, instead duplicating
the text of the error and returning a generic error

This means downstream error type checks were failing

Also remove some duplicated code/unnecessary code. It turns out that our
resolver emthods do not return return UnsupportedSeries errors

cmd/juju/application/deployer/charm.go

@@ -21,6 +21,7 @@ import (
 	"github.com/juju/juju/cmd/juju/application/utils"
 	"github.com/juju/juju/cmd/juju/common"
 	corebase "github.com/juju/juju/core/base"
+	corecharm "github.com/juju/juju/core/charm"
 	"github.com/juju/juju/core/constraints"
 	"github.com/juju/juju/core/devices"
 	"github.com/juju/juju/core/instance"
@@ -440,7 +441,7 @@ func (c *repositoryCharm) PrepareAndDeploy(ctx *cmd.Context, deployAPI DeployerA
 		}
 	}
 
-	if charm.IsUnsupportedSeriesError(err) {
+	if corecharm.IsUnsupportedSeriesError(err) {
 		msg := fmt.Sprintf("%v. Use --force to deploy the charm anyway.", err)
 		if usingDefaultSeries {
 			msg += " Used the default-series."

cmd/juju/application/deployer/charm_test.go

@@ -103,6 +103,7 @@ func (s *charmSuite) TestRepositoryCharmDeployDryRunDefaultSeriesForce(c *gc.C)
 	dCharm.validateCharmSeriesWithName = func(series, name string, imageStream string) error {
 		return nil
 	}
+
 	repoCharm := &repositoryCharm{
 		deployCharm:      *dCharm,
 		userRequestedURL: s.url,
@@ -129,6 +130,30 @@ func (s *charmSuite) TestRepositoryCharmDeployDryRunDefaultSeriesForce(c *gc.C)
 	c.Check(output.String(), gc.Equals, "\"testme\" from  charm \"testme\", revision -1 on ubuntu@22.04 would be deployed\n")
 }
 
+func (s *charmSuite) TestRepositoryCharmDeployDryRunUnsupportedSeries(c *gc.C) {
+	ctrl := s.setupMocks(c)
+	defer ctrl.Finish()
+	s.resolver = mocks.NewMockResolver(ctrl)
+	s.expectResolveChannel()
+	s.expectDeployerAPIModelGet(c, corebase.Base{})
+
+	dCharm := s.newDeployCharm()
+	dCharm.dryRun = true
+	dCharm.validateCharmSeriesWithName = func(series, name string, imageStream string) error {
+		return nil
+	}
+	dCharm.baseFlag = corebase.MustParseBaseFromString("ubuntu@12.04")
+
+	repoCharm := &repositoryCharm{
+		deployCharm:      *dCharm,
+		userRequestedURL: s.url,
+		clock:            clock.WallClock,
+	}
+
+	err := repoCharm.PrepareAndDeploy(s.ctx, s.deployerAPI, s.resolver)
+	c.Assert(err, gc.ErrorMatches, `series "precise" not supported by charm, .* Use --force to deploy the charm anyway.`)
+}
+
 func (s *charmSuite) newDeployCharm() *deployCharm {
 	return &deployCharm{
 		configOptions: s.configFlag,

cmd/juju/application/deployer/series_selector.go

@@ -141,10 +141,6 @@ func (s seriesSelector) userRequested(requestedSeries string) (string, error) {
 			if supported.IsEmpty() {
 				return "", errors.NewNotSupported(nil, fmt.Sprintf("series: %s", requestedSeries))
 			}
-			return "", errors.Errorf(
-				"series %q is not supported, supported series are: %s",
-				requestedSeries, strings.Join(supported.SortedValues(), ","),
-			)
 		}
 		return "", err
 	}

cmd/juju/application/deployer/series_selector_test.go

@@ -146,7 +146,7 @@ func (s *SeriesSelectorSuite) TestCharmSeries(c *gc.C) {
 				conf:                defaultBase{"ubuntu@15.10", true},
 				supportedJujuSeries: set.NewStrings("bionic", "cosmic"),
 			},
-			err: `series "wily" is not supported, supported series are: bionic,cosmic`,
+			err: `series "wily" not supported by charm, the charm supported series are: bionic,cosmic`,
 		},
 		{
 			title: "juju deploy multiseries   # use model series defaults if supported by charm",