[TEP-0076] Add indexing into array for params

This commit provides the indexing into array for params and gated by
alpha feature flag. Before this commit we can only refer to the whole
array param, with this feature we can refer to array's element such as
$(params.param-name[0]).

Author: Yongxuanzhang

docs/variables.md

@@ -19,6 +19,9 @@ For instructions on using variable substitutions see the relevant section of [th
 | `params.<param name>` | The value of the parameter at runtime. |
 | `params['<param name>']` | (see above) |
 | `params["<param name>"]` | (see above) |
+| `params.<param name>[i]` | Get the i-th element of param array. This is alpha feature, set `enable-api-fields` to `alpha`  to use it.|
+| `params['<param name>'][i]` | (see above) |
+| `params["<param name>"][i]` | (see above) |
 | `tasks.<taskName>.results.<resultName>` | The value of the `Task's` result. Can alter `Task` execution order within a `Pipeline`.) |
 | `tasks.<taskName>.results['<resultName>']` | (see above)) |
 | `tasks.<taskName>.results["<resultName>"]` | (see above)) |

examples/v1beta1/pipelineruns/alpha/pipelinerun-param-array-indexing.yaml

@@ -0,0 +1,58 @@
+apiVersion: tekton.dev/v1beta1
+kind: Pipeline
+metadata:
+  name: deploy
+spec:
+  params:
+    - name: environments
+      type: array
+  tasks:
+    - name: deploy
+      params:
+        - name: environment1
+          value: '$(params.environments[0])'
+        - name: environment2
+          value: '$(params.environments[1])'
+      taskSpec:
+        params:
+          - name: environment1
+            type: string
+          - name: environment2
+            type: string
+        steps:
+          # this step should echo "staging"
+          - name: echo-params-1
+            image: bash:3.2
+            args: [
+              "echo",
+              "$(params.environment1)",
+            ]
+          # this step should echo "staging"
+          - name: echo-params-2
+            image: ubuntu
+            script: |
+              #!/bin/bash
+              VALUE=$(params.environment2)
+              EXPECTED="qa"
+              diff=$(diff <(printf "%s\n" "${VALUE[@]}") <(printf "%s\n" "${EXPECTED[@]}"))
+              if [[ -z "$diff" ]]; then
+                  echo "Get expected: ${VALUE}"
+                  exit 0
+              else
+                  echo "Want: ${EXPECTED} Got: ${VALUE}"
+                  exit 1
+              fi
+---
+apiVersion: tekton.dev/v1beta1
+kind: PipelineRun
+metadata:
+  name: deployrun
+spec:
+  pipelineRef:
+    name: deploy
+  params:
+    - name: environments
+      value:
+        - 'staging'
+        - 'qa'
+        - 'prod'

pkg/apis/pipeline/v1beta1/param_types_test.go

@@ -230,6 +230,13 @@ func TestArrayOrString_ApplyReplacements(t *testing.T) {
 			arrayReplacements: map[string][]string{"params.myarray": {"a", "b", "c"}},
 		},
 		expectedOutput: v1beta1.NewArrayOrString("a", "b", "c"),
+	}, {
+		name: "array indexing replacement on string val",
+		args: args{
+			input:              v1beta1.NewArrayOrString("$(params.myarray[0])"),
+			stringReplacements: map[string]string{"params.myarray[0]": "a", "params.myarray[1]": "b"},
+		},
+		expectedOutput: v1beta1.NewArrayOrString("a"),
 	}, {
 		name: "object replacement on string val",
 		args: args{

pkg/reconciler/pipelinerun/pipelinerun.go

@@ -447,6 +447,15 @@ func (c *Reconciler) reconcile(ctx context.Context, pr *v1beta1.PipelineRun, get
 		return controller.NewPermanentError(err)
 	}
 
+	// Ensure that the array reference is not out of bound
+	if err := resources.ValidateParamArrayIndex(ctx, pipelineSpec, pr); err != nil {
+		// This Run has failed, so we need to mark it as failed and stop reconciling it
+		pr.Status.MarkFailed(ReasonObjectParameterMissKeys,
+			"PipelineRun %s/%s parameters is missing object keys required by Pipeline %s/%s's parameters: %s",
+			pr.Namespace, pr.Name, pr.Namespace, pipelineMeta.Name, err)
+		return controller.NewPermanentError(err)
+	}
+
 	// Ensure that the workspaces expected by the Pipeline are provided by the PipelineRun.
 	if err := resources.ValidateWorkspaceBindings(pipelineSpec, pr); err != nil {
 		pr.Status.MarkFailed(ReasonInvalidWorkspaceBinding,

pkg/reconciler/pipelinerun/resources/apply.go

@@ -39,6 +39,7 @@ func ApplyParameters(ctx context.Context, p *v1beta1.PipelineSpec, pr *v1beta1.P
 	stringReplacements := map[string]string{}
 	arrayReplacements := map[string][]string{}
 	objectReplacements := map[string]map[string]string{}
+	cfg := config.FromContextOrDefaults(ctx)
 
 	patterns := []string{
 		"params.%s",
@@ -55,6 +56,12 @@ func ApplyParameters(ctx context.Context, p *v1beta1.PipelineSpec, pr *v1beta1.P
 			switch p.Default.Type {
 			case v1beta1.ParamTypeArray:
 				for _, pattern := range patterns {
+					// array indexing for param is alpha feature
+					if cfg.FeatureFlags.EnableAPIFields == config.AlphaAPIFields {
+						for i := 0; i < len(p.Default.ArrayVal); i++ {
+							stringReplacements[fmt.Sprintf(pattern+"[%d]", p.Name, i)] = p.Default.ArrayVal[i]
+						}
+					}
 					arrayReplacements[fmt.Sprintf(pattern, p.Name)] = p.Default.ArrayVal
 				}
 			case v1beta1.ParamTypeObject:
@@ -76,6 +83,12 @@ func ApplyParameters(ctx context.Context, p *v1beta1.PipelineSpec, pr *v1beta1.P
 		switch p.Value.Type {
 		case v1beta1.ParamTypeArray:
 			for _, pattern := range patterns {
+				// array indexing for param is alpha feature
+				if cfg.FeatureFlags.EnableAPIFields == config.AlphaAPIFields {
+					for i := 0; i < len(p.Value.ArrayVal); i++ {
+						stringReplacements[fmt.Sprintf(pattern+"[%d]", p.Name, i)] = p.Value.ArrayVal[i]
+					}
+				}
 				arrayReplacements[fmt.Sprintf(pattern, p.Name)] = p.Value.ArrayVal
 			}
 		case v1beta1.ParamTypeObject: