Add validation for duplicated param names in TaskSpec

Prior to this, when duplicated names for parameters were assigned in `taskSpec`, the param value would be overwritten by the last value.

To avoid this, a validation check was added to ensure that no param name is duplicated in TaskSpec.

pkg/apis/pipeline/v1beta1/task_validation.go

@@ -321,8 +321,12 @@ func ValidateParameterVariables(steps []Step, params []ParamSpec) *apis.FieldErr
 	parameterNames := sets.NewString()
 	arrayParameterNames := sets.NewString()
 	objectParamSpecs := []ParamSpec{}
-
+	var errs *apis.FieldError
 	for _, p := range params {
+		// validate no duplicate names
+		if parameterNames.Has(p.Name) {
+			errs = errs.Also(apis.ErrGeneric("parameter appears more than once", "").ViaFieldKey("params", p.Name))
+		}
 		parameterNames.Insert(p.Name)
 		if p.Type == ParamTypeArray {
 			arrayParameterNames.Insert(p.Name)
@@ -332,7 +336,7 @@ func ValidateParameterVariables(steps []Step, params []ParamSpec) *apis.FieldErr
 		}
 	}
 
-	errs := validateVariables(steps, "params", parameterNames)
+	errs = errs.Also(validateVariables(steps, "params", parameterNames))
 	errs = errs.Also(validateArrayUsage(steps, "params", arrayParameterNames))
 	return errs.Also(validateObjectUsage(steps, objectParamSpecs))
 }

pkg/apis/pipeline/v1beta1/task_validation_test.go

@@ -529,6 +529,26 @@ func TestTaskSpecValidateError(t *testing.T) {
 			Paths:   []string{"params"},
 			Details: "Names: \nMust only contain alphanumeric characters, hyphens (-), underscores (_), and dots (.)\nMust begin with a letter or an underscore (_)",
 		},
+	}, {
+		name: "duplicated param names",
+		fields: fields{
+			Params: []v1beta1.ParamSpec{{
+				Name:        "foo",
+				Type:        v1beta1.ParamTypeString,
+				Description: "parameter",
+				Default:     v1beta1.NewArrayOrString("value1"),
+			}, {
+				Name:        "foo",
+				Type:        v1beta1.ParamTypeString,
+				Description: "parameter",
+				Default:     v1beta1.NewArrayOrString("value2"),
+			}},
+			Steps: validSteps,
+		},
+		expectedError: apis.FieldError{
+			Message: `parameter appears more than once`,
+			Paths:   []string{"params[foo]"},
+		},
 	}, {
 		name: "invalid param type",
 		fields: fields{