[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 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)) |
@@ -38,6 +41,9 @@ 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 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) |
 | `resources.inputs.<resourceName>.path` | The path to the input resource's directory. |
 | `resources.outputs.<resourceName>.path` | The path to the output resource's directory. |
 | `results.<resultName>.path` | The path to the file where the `Task` writes its results data. |

examples/v1beta1/taskruns/alpha/param_array_indexing.yaml

@@ -0,0 +1,22 @@
+apiVersion: tekton.dev/v1beta1
+kind: TaskRun
+metadata:
+  name: array-with-default-1
+spec:
+  params:
+    - name: array-to-echo
+      value:
+        - "foo"
+        - "bar"
+  taskSpec:
+    params:
+      - name: array-to-echo
+        type: array
+    steps:
+      # this step should echo "foo"
+      - name: echo-params
+        image: bash:3.2
+        args: [
+          "echo",
+          "$(params.array-to-echo[0])",
+        ]

pkg/reconciler/pipelinerun/pipelinerun.go

@@ -454,7 +454,7 @@ func (c *Reconciler) reconcile(ctx context.Context, pr *v1beta1.PipelineRun, get
 	}
 
 	// Apply parameter substitution from the PipelineRun
-	pipelineSpec = resources.ApplyParameters(pipelineSpec, pr)
+	pipelineSpec = resources.ApplyParameters(ctx, pipelineSpec, pr)
 	pipelineSpec = resources.ApplyContexts(pipelineSpec, pipelineMeta.Name, pr)
 	pipelineSpec = resources.ApplyWorkspaces(pipelineSpec, pr)
 

pkg/reconciler/pipelinerun/resources/apply.go

@@ -17,24 +17,27 @@ limitations under the License.
 package resources
 
 import (
+	"context"
 	"fmt"
 	"strconv"
 	"strings"
 
+	"github.com/tektoncd/pipeline/pkg/apis/config"
 	"github.com/tektoncd/pipeline/pkg/apis/run/v1alpha1"
 
 	"github.com/tektoncd/pipeline/pkg/apis/pipeline/v1beta1"
 	"github.com/tektoncd/pipeline/pkg/substitution"
 )
 
 // ApplyParameters applies the params from a PipelineRun.Params to a PipelineSpec.
-func ApplyParameters(p *v1beta1.PipelineSpec, pr *v1beta1.PipelineRun) *v1beta1.PipelineSpec {
+func ApplyParameters(ctx context.Context, p *v1beta1.PipelineSpec, pr *v1beta1.PipelineRun) *v1beta1.PipelineSpec {
 	// This assumes that the PipelineRun inputs have been validated against what the Pipeline requests.
 
 	// stringReplacements is used for standard single-string stringReplacements, while arrayReplacements contains arrays
 	// that need to be further processed.
 	stringReplacements := map[string]string{}
 	arrayReplacements := map[string][]string{}
+	cfg := config.FromContextOrDefaults(ctx)
 
 	patterns := []string{
 		"params.%s",
@@ -51,6 +54,12 @@ func ApplyParameters(p *v1beta1.PipelineSpec, pr *v1beta1.PipelineRun) *v1beta1.
 				}
 			} else {
 				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
 				}
 			}
@@ -64,6 +73,12 @@ func ApplyParameters(p *v1beta1.PipelineSpec, pr *v1beta1.PipelineRun) *v1beta1.
 			}
 		} else {
 			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
 			}
 		}