[TEP-0076] Add indexing into array for pipeline params reference

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: