Remove empty pipeline validation

cli/run_util_pipeline_test.go

@@ -140,6 +140,15 @@ workflows:
   c: {}
 `
 
+const emptyPipeline = `
+format_version: '13'
+pipelines:
+  dag:
+    workflows: {}
+workflows:
+  a: {}
+`
+
 func TestValidation(t *testing.T) {
 	tests := []struct {
 		name    string
@@ -184,6 +193,10 @@ func TestValidation(t *testing.T) {
 			name:   "Valid staged pipeline",
 			config: validStagedPipeline,
 		},
+		{
+			name:   "Empty pipeline",
+			config: emptyPipeline,
+		},
 		{
 			name: "The last pipeline is invalid",
 			config: `

models/models_methods.go

@@ -559,8 +559,12 @@ func validatePipelines(config *BitriseDataModel) ([]string, error) {
 
 		if hasStages && hasWorkflows {
 			return pipelineWarnings, fmt.Errorf("pipeline (%s) has both stages and workflows", pipelineID)
-		} else if !hasStages && !hasWorkflows {
-			return pipelineWarnings, fmt.Errorf("pipeline (%s) should have at least 1 stage or workflow", pipelineID)
+		}
+
+		// A pipeline is considered valid if it has neither stages nor workflows.
+		// This is useful for the WFE to be able to save a pipeline that is not yet fully defined.
+		if !hasStages && !hasWorkflows {
+			continue
 		}
 
 		if hasStages {