fix: Consider missing optional input/output artifacts with same name

test/e2e/functional_test.go

@@ -404,7 +404,7 @@ func (s *FunctionalSuite) TestStopBehavior() {
 			assert.NoError(t, err)
 			assert.Contains(t, output, "workflow stop-terminate stopped")
 		}).
-		WaitForWorkflow(30 * time.Second).
+		WaitForWorkflow(45 * time.Second).
 		Then().
 		ExpectWorkflow(func(t *testing.T, _ *metav1.ObjectMeta, status *wfv1.WorkflowStatus) {
 			assert.Equal(t, wfv1.NodeFailed, status.Phase)
@@ -495,6 +495,18 @@ spec:
 		})
 }
 
+func (s *FunctionalSuite) TestSameInputOutputPathOptionalArtifact() {
+	s.Given().
+		Workflow("@testdata/same-input-output-path-optional.yaml").
+		When().
+		SubmitWorkflow().
+		WaitForWorkflow(30 * time.Second).
+		Then().
+		ExpectWorkflow(func(t *testing.T, _ *metav1.ObjectMeta, status *wfv1.WorkflowStatus) {
+			assert.Equal(t, wfv1.NodeSucceeded, status.Phase)
+		})
+}
+
 func TestFunctionalSuite(t *testing.T) {
 	suite.Run(t, new(FunctionalSuite))
 }

test/e2e/testdata/same-input-output-path-optional.yaml

@@ -0,0 +1,33 @@
+apiVersion: argoproj.io/v1alpha1
+kind: Workflow
+metadata:
+  generateName: optional-input-output-artifact-same-location-
+  labels:
+    argo-e2e: true
+spec:
+  entrypoint: plan
+  templates:
+    - name: plan
+      steps:
+        - - name: write
+            template: file
+        - - name: read
+            template: file
+            arguments:
+              artifacts:
+                - name: file
+                  from: "{{steps.write.outputs.artifacts.file}}"
+    - name: file
+      inputs:
+        artifacts:
+          - name: file
+            path: /tmp/file1.txt
+            optional: true
+      container:
+        image: argoproj/argosay:v2
+        args: ["echo", "test", "/tmp/file1.txt"]
+      outputs:
+        artifacts:
+          - name: file
+            path: /tmp/file1.txt
+

workflow/executor/executor.go

@@ -414,6 +414,12 @@ func (we *WorkflowExecutor) isBaseImagePath(path string) bool {
 	// next check if path overlaps with a shared input-artifact emptyDir mounted by argo
 	for _, inArt := range we.Template.Inputs.Artifacts {
 		if path == inArt.Path {
+			// The input artifact may have been optional and not supplied. If this is the case, the file won't exist on
+			// the input artifact volume. Since this function was called, we know that we want to use this path as an
+			// ourput artifact, so we should look for it in the base image path.
+			if inArt.Optional && !inArt.HasLocation() {
+				return true
+			}
 			return false
 		}
 		if strings.HasPrefix(path, inArt.Path+"/") {