Added Validation: Matrix parameters cannot be empty arrays

Added a check in Pipeline validation to verify that matrix parameters are not just arrays, but that they are not empty arrays. This won't change existing functionality/capabilities, but will get rid of the panic in the reconciler.

docs/matrix.md

@@ -24,7 +24,7 @@ weight: 11
 ## Overview
 
 `Matrix` is used to fan out `Tasks` in a `Pipeline`. This doc will explain the details of `matrix` support in
-Tekton. 
+Tekton.
 
 Documentation for specifying `Matrix` in a `Pipeline`:
 - [Specifying `Matrix` in `Tasks`](pipelines.md#specifying-matrix-in-pipelinetasks)
@@ -40,12 +40,12 @@ A `Matrix` supports the following features:
 * [Concurrency Control](#concurrency-control)
 * [Parameters](#parameters)
 * [Context Variables](#context-variables)
-* [Results](#results) 
+* [Results](#results)
 
 ### Concurrency Control
 
 The default maximum count of `TaskRuns` or `Runs` from a given `Matrix` is **256**. To customize the maximum count of
-`TaskRuns` or `Runs` generated from a given `Matrix`, configure the `default-max-matrix-combinations-count` in 
+`TaskRuns` or `Runs` generated from a given `Matrix`, configure the `default-max-matrix-combinations-count` in
 [config defaults](/config/config-defaults.yaml). When a `Matrix` in `PipelineTask` would generate more than the maximum
 `TaskRuns` or `Runs`, the `Pipeline` validation would fail.
 
@@ -69,6 +69,7 @@ The `Matrix` will take `Parameters` of type `"array"` only, which will be suppli
 `PipelineTask` by substituting `Parameters` of type `"string"` in the underlying `Task`.
 The names of the `Parameters` in the `Matrix` must match the names of the `Parameters`
 in the underlying `Task` that they will be substituting.
+Note: The `Paramaters` of type `array` cannot be empty.
 
 In the example below, the *test* `Task` takes *browser* and *platform* `Parameters` of type
 `"string"`. A `Pipeline` used to fan out the `Task` using `Matrix` would have two `Parameters`
@@ -92,7 +93,7 @@ spec:
       default:
         - chrome
         - safari
-        - firefox    
+        - firefox
   tasks:
   - name: fetch-repository
     taskRef:
@@ -110,7 +111,7 @@ spec:
   ...
 ```
 
-A `Parameter` can be passed to either the `matrix` or `params` field, not both. 
+A `Parameter` can be passed to either the `matrix` or `params` field, not both.
 
 For further details on specifying `Parameters` in the `Pipeline` and passing them to
 `PipelineTasks`, see [documentation](pipelines.md#specifying-parameters).
@@ -150,7 +151,7 @@ spec:
 
 ### Context Variables
 
-Similarly to the `Parameters` in the `Params` field, the `Parameters` in the `Matrix` field will accept 
+Similarly to the `Parameters` in the `Params` field, the `Parameters` in the `Matrix` field will accept
 [context variables](variables.md) that will be substituted, including:
 
 * `PipelineRun` name, namespace and uid
@@ -161,7 +162,7 @@ Similarly to the `Parameters` in the `Params` field, the `Parameters` in the `Ma
 
 #### Specifying Results in a Matrix
 
-Consuming `Results` from previous `TaskRuns` or `Runs` in a `Matrix`, which would dynamically generate 
+Consuming `Results` from previous `TaskRuns` or `Runs` in a `Matrix`, which would dynamically generate
 `TaskRuns` or `Runs` from the fanned out `PipelineTask`, is supported. Producing `Results` in from a
 `PipelineTask` with a `Matrix` is not yet supported - see [further details](#results-from-fanned-out-pipelinetasks).
 
@@ -203,7 +204,7 @@ tasks:
 
 Consuming `Results` from fanned out `PipelineTasks` will not be in the supported in the initial iteration
 of `Matrix`. Supporting consuming `Results` from fanned out `PipelineTasks` will be revisited after array
-and object `Results` are supported. 
+and object `Results` are supported.
 
 ## Fan Out
 
@@ -487,15 +488,15 @@ status:
         name: platforms-and-browsers
         taskRef:
           apiVersion: cel.tekton.dev/v1alpha1
-          kind: CEL  
+          kind: CEL
   startTime: "2022-06-28T20:49:40Z"
   completionTime: "2022-06-28T20:49:41Z"
   conditions:
     - lastTransitionTime: "2022-06-28T20:49:41Z"
       message: 'Tasks Completed: 1 (Failed: 0, Cancelled 0), Skipped: 0'
       reason: Succeeded
       status: "True"
-      type: Succeeded  
+      type: Succeeded
   childReferences:
     - apiVersion: tekton.dev/v1alpha1
       kind: Run
@@ -533,11 +534,11 @@ status:
 
 ## Retries
 
-The `retries` field is used to specify the number of times a `PipelineTask` should be retried when its `TaskRun` or 
-`Run` fails, see the [documentation][retries] for further details. When a `PipelineTask` is fanned out using `Matrix`, 
+The `retries` field is used to specify the number of times a `PipelineTask` should be retried when its `TaskRun` or
+`Run` fails, see the [documentation][retries] for further details. When a `PipelineTask` is fanned out using `Matrix`,
 a given `TaskRun` or `Run` executed will be retried as much as the field in the `retries` field of the `PipelineTask`.
 
-For example, the `PipelineTask` in this `PipelineRun` will be fanned out into three `TaskRuns` each of which will be 
+For example, the `PipelineTask` in this `PipelineRun` will be fanned out into three `TaskRuns` each of which will be
 retried once:
 
 ```yaml

pkg/apis/pipeline/v1/param_types.go

@@ -331,6 +331,9 @@ func validateParametersInTaskMatrix(matrix *Matrix) (errs *apis.FieldError) {
 			if param.Value.Type != ParamTypeArray {
 				errs = errs.Also(apis.ErrInvalidValue("parameters of type array only are allowed in matrix", "").ViaFieldKey("matrix", param.Name))
 			}
+			if param.Value.Type == ParamTypeArray && len(param.Value.ArrayVal) == 0 {
+				errs = errs.Also(apis.ErrInvalidValue("empty arrays not allowed as parameters in matrix", "").ViaFieldKey("matrix", param.Name))
+			}
 		}
 	}
 	return errs

pkg/apis/pipeline/v1/pipeline_types_test.go

@@ -645,6 +645,21 @@ func TestPipelineTask_validateMatrix(t *testing.T) {
 					Name: "barfoo", Value: ParamValue{Type: ParamTypeArray, ArrayVal: []string{"bar", "foo"}},
 				}}},
 		},
+	}, {
+		name: "parameters in matrix are not empty arrays",
+		pt: &PipelineTask{
+			Name: "task",
+			Matrix: &Matrix{
+				Params: []Param{{
+					Name: "foobar", Value: ParamValue{Type: ParamTypeArray, ArrayVal: []string{}},
+				}, {
+					Name: "barfoo", Value: ParamValue{Type: ParamTypeArray, ArrayVal: []string{}},
+				}}},
+		},
+		wantErrs: &apis.FieldError{
+			Message: "invalid value: empty arrays not allowed as parameters in matrix",
+			Paths:   []string{"matrix[barfoo]", "matrix[foobar]"},
+		},
 	}, {
 		name: "parameters in matrix contain results references",
 		pt: &PipelineTask{

pkg/apis/pipeline/v1beta1/param_types.go

@@ -325,6 +325,9 @@ func validateParametersInTaskMatrix(matrix *Matrix) (errs *apis.FieldError) {
 			if param.Value.Type != ParamTypeArray {
 				errs = errs.Also(apis.ErrInvalidValue("parameters of type array only are allowed in matrix", "").ViaFieldKey("matrix", param.Name))
 			}
+			if param.Value.Type == ParamTypeArray && len(param.Value.ArrayVal) == 0 {
+				errs = errs.Also(apis.ErrInvalidValue("empty arrays not allowed as parameters in matrix", "").ViaFieldKey("matrix", param.Name))
+			}
 		}
 	}
 	return errs

pkg/apis/pipeline/v1beta1/pipeline_types_test.go

@@ -831,6 +831,21 @@ func TestPipelineTask_validateMatrix(t *testing.T) {
 					Name: "barfoo", Value: ParamValue{Type: ParamTypeArray, ArrayVal: []string{"bar", "foo"}},
 				}}},
 		},
+	}, {
+		name: "parameters in matrix are not empty arrays",
+		pt: &PipelineTask{
+			Name: "task",
+			Matrix: &Matrix{
+				Params: []Param{{
+					Name: "foobar", Value: ParamValue{Type: ParamTypeArray, ArrayVal: []string{}},
+				}, {
+					Name: "barfoo", Value: ParamValue{Type: ParamTypeArray, ArrayVal: []string{}},
+				}}},
+		},
+		wantErrs: &apis.FieldError{
+			Message: "invalid value: empty arrays not allowed as parameters in matrix",
+			Paths:   []string{"matrix[barfoo]", "matrix[foobar]"},
+		},
 	}, {
 		name: "parameters in matrix contain results references",
 		pt: &PipelineTask{