Feat/3140/better error message on mixin missing (#3145)

* WIP: Add extra error when mixin missing

Signed-off-by: David Gannon <19214156+dgannon991@users.noreply.github.com>

* Added more information to the error message

Signed-off-by: David Gannon <19214156+dgannon991@users.noreply.github.com>

---------

Signed-off-by: David Gannon <19214156+dgannon991@users.noreply.github.com>
Co-authored-by: schristoff <28318173+schristoff@users.noreply.github.com>

pkg/linter/linter.go

@@ -210,7 +210,7 @@ func (l *Linter) Lint(ctx context.Context, m *manifest.Manifest) (Results, error
 			return nil, span.Error(fmt.Errorf("error validating action: %s", action.name))
 		}
 		results = append(results, res...)
-  }
+	}
 
 	deps := make(map[string]interface{}, len(m.Dependencies.Requires))
 	for _, dep := range m.Dependencies.Requires {
@@ -247,6 +247,10 @@ func (l *Linter) Lint(ctx context.Context, m *manifest.Manifest) (Results, error
 			if strings.Contains(response.Error.Error(), "unknown command") {
 				continue
 			}
+			// put a helpful error when the mixin is not installed
+			if strings.Contains(response.Error.Error(), "not installed") {
+				return nil, span.Error(fmt.Errorf("mixin %[1]s is not currently installed. To find view more details you can run: porter mixin search %[1]s. To install you can run porter mixin install %[1]s", response.Name))
+			}
 			return nil, span.Error(fmt.Errorf("lint command failed for mixin %s: %s", response.Name, response.Stdout))
 		}