Use values in relationship To/From fields (#2871)

* use pkg values in relationship fields

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

* add linter rule for using values in relationships

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

* use new cmptest package for comparing relationships

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

* create cmptest for common cmp.Diff options in test

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

* condense matches for relationship ruleguard

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

* remove relationship type from rules

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

* restore build tag

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

* suggest using values

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

* nil check pkgs

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

---------

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

internal/relationship/by_file_ownership.go

@@ -58,9 +58,19 @@ func byFileOwnershipOverlap(catalog *pkg.Collection) []artifact.Relationship {
 			parent := catalog.Package(parentID) // TODO: this is potentially expensive
 			child := catalog.Package(childID)   // TODO: this is potentially expensive
 
+			if parent == nil {
+				log.Tracef("parent package not found: %v", parentID)
+				continue
+			}
+
+			if child == nil {
+				log.Tracef("child package not found: %v", childID)
+				continue
+			}
+
 			edges = append(edges, artifact.Relationship{
-				From: parent,
-				To:   child,
+				From: *parent,
+				To:   *child,
 				Type: artifact.OwnershipByFileOverlapRelationship,
 				Data: ownershipByFilesMetadata{
 					Files: fs,