Avoid 500 panic error when uploading invalid maven package file (#31014)

PackageDescriptor.Metadata might be nil (and maybe not only for maven).
This is only a quick fix.

The new `if` block is written intentionally to avoid unnecessary
indenting to the existing code.

options/locale/locale_en-US.ini

@@ -3415,6 +3415,7 @@ error.unit_not_allowed = You are not allowed to access this repository section.
 title = Packages
 desc = Manage repository packages.
 empty = There are no packages yet.
+no_metadata = No metadata.
 empty.documentation = For more information on the package registry, see <a target="_blank" rel="noopener noreferrer" href="%s">the documentation</a>.
 empty.repo = Did you upload a package, but it's not shown here? Go to <a href="%[1]s">package settings</a> and link it to this repo.
 registry.documentation = For more information on the %s registry, see <a target="_blank" rel="noopener noreferrer" href="%s">the documentation</a>.

templates/package/content/maven.tmpl

@@ -1,4 +1,8 @@
-{{if eq .PackageDescriptor.Package.Type "maven"}}
+{{if and (eq .PackageDescriptor.Package.Type "maven") (not .PackageDescriptor.Metadata)}}
+	<h4 class="ui top attached header">{{ctx.Locale.Tr "packages.installation"}}</h4>
+	<div class="ui attached segment">{{ctx.Locale.Tr "packages.no_metadata"}}</div>
+{{end}}
+{{if and (eq .PackageDescriptor.Package.Type "maven") .PackageDescriptor.Metadata}}
 	<h4 class="ui top attached header">{{ctx.Locale.Tr "packages.installation"}}</h4>
 	<div class="ui attached segment">
 		<div class="ui form">

templates/package/metadata/maven.tmpl

@@ -1,4 +1,7 @@
-{{if eq .PackageDescriptor.Package.Type "maven"}}
+{{if and (eq .PackageDescriptor.Package.Type "maven") (not .PackageDescriptor.Metadata)}}
+	<div class="item">{{svg "octicon-note" 16 "tw-mr-2"}} {{ctx.Locale.Tr "packages.no_metadata"}}</div>
+{{end}}
+{{if and (eq .PackageDescriptor.Package.Type "maven") .PackageDescriptor.Metadata}}
 	{{if .PackageDescriptor.Metadata.Name}}<div class="item">{{svg "octicon-note" 16 "tw-mr-2"}} {{.PackageDescriptor.Metadata.Name}}</div>{{end}}
 	{{if .PackageDescriptor.Metadata.ProjectURL}}<div class="item">{{svg "octicon-link-external" 16 "tw-mr-2"}} <a href="{{.PackageDescriptor.Metadata.ProjectURL}}" target="_blank" rel="noopener noreferrer me">{{ctx.Locale.Tr "packages.details.project_site"}}</a></div>{{end}}
 	{{range .PackageDescriptor.Metadata.Licenses}}<div class="item" title="{{ctx.Locale.Tr "packages.details.license"}}">{{svg "octicon-law" 16 "tw-mr-2"}} {{.}}</div>{{end}}

tests/integration/api_packages_maven_test.go

@@ -15,6 +15,7 @@ import (
 	"code.gitea.io/gitea/models/unittest"
 	user_model "code.gitea.io/gitea/models/user"
 	"code.gitea.io/gitea/modules/packages/maven"
+	"code.gitea.io/gitea/modules/test"
 	"code.gitea.io/gitea/tests"
 
 	"github.com/stretchr/testify/assert"
@@ -241,4 +242,13 @@ func TestPackageMaven(t *testing.T) {
 		putFile(t, fmt.Sprintf("/%s/maven-metadata.xml", snapshotVersion), "test", http.StatusCreated)
 		putFile(t, fmt.Sprintf("/%s/maven-metadata.xml", snapshotVersion), "test-overwrite", http.StatusCreated)
 	})
+
+	t.Run("InvalidFile", func(t *testing.T) {
+		ver := packageVersion + "-invalid"
+		putFile(t, fmt.Sprintf("/%s/%s", ver, filename), "any invalid content", http.StatusCreated)
+		req := NewRequestf(t, "GET", "/%s/-/packages/maven/%s-%s/%s", user.Name, groupID, artifactID, ver)
+		resp := MakeRequest(t, req, http.StatusOK)
+		assert.Contains(t, resp.Body.String(), "No metadata.")
+		assert.True(t, test.IsNormalPageCompleted(resp.Body.String()))
+	})
 }