Add example and docs for array param with defaults 📜

While working on (finally) updating the array result and object
param/result TEPs (tektoncd/community#479
tektoncd/community#477) I realized I hadn't
included an example of how to specify defaults for the new format, so I
looked for an example of how we currently do this for arrays, but we had
none! Hopefully now we do :D

docs/pipelines.md

@@ -149,6 +149,8 @@ For more information, see:
 
 ## Specifying `Parameters`
 
+(See also [Specifying Parameters in Tasks](tasks.md#specifying-parameters))
+
 You can specify global parameters, such as compilation flags or artifact names, that you want to supply
 to the `Pipeline` at execution time. `Parameters` are passed to the `Pipeline` from its corresponding
 `PipelineRun` and can replace template values specified within each `Task` in the `Pipeline`.

docs/tasks.md

@@ -502,6 +502,26 @@ spec:
       value: "http://google.com"
 ```
 
+Parameter declarations (within Tasks and Pipelines) can include default values which will be used if the parameter is
+not specified, for example to specify defaults for both string params and array params
+([full example](../examples/v1beta1/taskruns/array-default.yaml)) :
+
+```yaml
+apiVersion: tekton.dev/v1beta1
+kind: Task
+metadata:
+  name: task-with-array-default
+spec:
+  params:
+    - name: flags
+      type: array
+      default:
+        - "--set"
+        - "arg1=foo"
+        - "--randomflag"
+        - "--someotherflag"
+```
+
 ### Specifying `Resources`
 
 > :warning: **`PipelineResources` are [deprecated](deprecations.md#deprecation-table).**

examples/v1beta1/taskruns/array-default.yaml

@@ -0,0 +1,32 @@
+apiVersion: tekton.dev/v1beta1
+kind: TaskRun
+metadata:
+  generateName: array-with-default-
+spec:
+  params:
+    - name: array-to-echo
+      value:
+        - "foo"
+        - "bar"
+  taskSpec:
+    params:
+      - name: array-to-echo
+        type: array
+      - name: another-array-to-echo
+        type: array
+        default:
+        - "foo-default"
+        - "bar-default"
+      - name: string-to-echo
+        type: string
+        default: "baz"
+    steps:
+      # this step should echo "foo bar foo-default bar-default baz"
+      - name: echo-params
+        image: bash:3.2
+        args: [
+          "echo",
+          "$(params.array-to-echo[*])",
+          "$(params.another-array-to-echo[*])",
+          "$(params.string-to-echo)",
+        ]