Follow convention for naming catalogers (#2277)

* follow convention for naming catalogers

Signed-off-by: Alex Goodman <wagoodman@users.noreply.github.com>

* fix cataloger name example

Signed-off-by: Alex Goodman <wagoodman@users.noreply.github.com>

---------

Signed-off-by: Alex Goodman <wagoodman@users.noreply.github.com>

syft/pkg/cataloger/arch/package.go

@@ -0,0 +1,54 @@
+package arch
+
+import (
+	"strings"
+
+	"github.com/anchore/packageurl-go"
+	"github.com/anchore/syft/syft/file"
+	"github.com/anchore/syft/syft/linux"
+	"github.com/anchore/syft/syft/pkg"
+)
+
+func newPackage(m *parsedData, release *linux.Release, dbLocation file.Location) pkg.Package {
+	licenseCandidates := strings.Split(m.Licenses, "\n")
+
+	p := pkg.Package{
+		Name:      m.Package,
+		Version:   m.Version,
+		Locations: file.NewLocationSet(dbLocation),
+		Licenses:  pkg.NewLicenseSet(pkg.NewLicensesFromLocation(dbLocation.WithoutAnnotations(), licenseCandidates...)...),
+		Type:      pkg.AlpmPkg,
+		PURL:      packageURL(m, release),
+		Metadata:  m.AlpmDBEntry,
+	}
+	p.SetID()
+
+	return p
+}
+
+func packageURL(m *parsedData, distro *linux.Release) string {
+	if distro == nil || distro.ID != "arch" {
+		// note: there is no namespace variation (like with debian ID_LIKE for ubuntu ID, for example)
+		return ""
+	}
+
+	qualifiers := map[string]string{
+		pkg.PURLQualifierArch: m.Architecture,
+	}
+
+	if m.BasePackage != "" {
+		qualifiers[pkg.PURLQualifierUpstream] = m.BasePackage
+	}
+
+	return packageurl.NewPackageURL(
+		"alpm", // `alpm` for Arch Linux and other users of the libalpm/pacman package manager. (see https://github.com/package-url/purl-spec/pull/164)
+		distro.ID,
+		m.Package,
+		m.Version,
+		pkg.PURLQualifiers(
+			qualifiers,
+			distro,
+		),
+		"",
+	).ToString()
+}