Address conflicting bases by converting resources into patches

pkg/accumulator/resaccumulator.go

@@ -6,10 +6,12 @@ package accumulator
 import (
 	"fmt"
 	"log"
+	"reflect"
 	"strings"
 
 	"sigs.k8s.io/kustomize/v3/pkg/resid"
 	"sigs.k8s.io/kustomize/v3/pkg/resmap"
+	"sigs.k8s.io/kustomize/v3/pkg/resource"
 	"sigs.k8s.io/kustomize/v3/pkg/transformers"
 	"sigs.k8s.io/kustomize/v3/pkg/transformers/config"
 	"sigs.k8s.io/kustomize/v3/pkg/types"
@@ -42,6 +44,36 @@ func (ra *ResAccumulator) Vars() []types.Var {
 	return ra.varSet.AsSlice()
 }
 
+// RemoveIds removes resources of the internal resMap which are member
+// of the resId slice past in parameter.
+// The removed Resources are returned by the method.
+func (ra *ResAccumulator) RemoveConflicts(rightResources []*resource.Resource) ([]*resource.Resource, error) {
+	conflicting := []*resource.Resource{}
+	for _, rightResource := range rightResources {
+		rightId := rightResource.CurId()
+		leftResources := ra.resMap.GetMatchingResourcesByCurrentId(rightId.Equals)
+
+		if len(leftResources) == 0 {
+			// no conflict
+			continue
+		}
+
+		if len(leftResources) != 1 || !reflect.DeepEqual(leftResources[0], rightResource) {
+			// conflict detected. More than one resource or left and right are different.
+			conflicting = append(conflicting, leftResources...)
+		}
+
+		// Remove the resource from that resMap
+		err := ra.resMap.Remove(rightId)
+		if err != nil {
+			return nil, err
+		}
+	}
+	return conflicting, nil
+}
+
+// AllIds returns all CurrentIds.
+
 func (ra *ResAccumulator) AppendAll(
 	resources resmap.ResMap) error {
 	return ra.resMap.AppendAll(resources)

pkg/target/diamondcomposition_test.go

@@ -4,7 +4,6 @@
 package target_test
 
 import (
-	"strings"
 	"testing"
 
 	kusttest_test "sigs.k8s.io/kustomize/v3/pkg/kusttest"
@@ -125,14 +124,11 @@ resources:
 - ../restart
 `)
 
-	_, err := th.MakeKustTarget().MakeCustomizedResMap()
-	if err == nil {
-		t.Fatalf("Expected resource accumulation error")
-	}
-	if !strings.Contains(
-		err.Error(), "already registered id: apps_v1_Deployment|~X|my-deployment") {
-		t.Fatalf("Unexpected err: %v", err)
+	m, err := th.MakeKustTarget().MakeCustomizedResMap()
+	if err != nil {
+		t.Fatalf("Err: %v", err)
 	}
+	th.AssertActualEqualsExpected(m, expectedPatchedDeployment)
 }
 
 const expectedPatchedDeployment = `

pkg/target/kusttarget.go

@@ -330,6 +330,24 @@ func (kt *KustTarget) configureExternalTransformers() ([]transformers.Transforme
 	return kt.pLdr.LoadTransformers(kt.ldr, ra.ResMap())
 }
 
+func (kt *KustTarget) solveConflicts(ra *accumulator.ResAccumulator, subRa *accumulator.ResAccumulator) error {
+	conflicting, err := subRa.RemoveConflicts(ra.ResMap().Resources())
+	if err != nil {
+		return errors.Wrapf(
+			err, "converting diamond imported resources into patches %v",
+			subRa.ResMap().AllIds())
+	}
+
+	if len(conflicting) == 0 {
+		return nil
+	}
+	t, err := kt.tFactory.MakePatchTransformer((conflicting), kt.rFactory.RF())
+	if err != nil {
+		return err
+	}
+	return ra.Transform(t)
+}
+
 // accumulateResources fills the given resourceAccumulator
 // with resources read from the given list of paths.
 func (kt *KustTarget) accumulateResources(
@@ -364,6 +382,11 @@ func (kt *KustTarget) accumulateDirectory(
 		return errors.Wrapf(
 			err, "recursed accumulation of path '%s'", path)
 	}
+	err = subKt.solveConflicts(ra, subRa)
+	if err != nil {
+		return errors.Wrapf(
+			err, "recursed merging from path '%s'", path)
+	}
 	err = ra.MergeAccumulator(subRa)
 	if err != nil {
 		return errors.Wrapf(