docs: Add guide to showcase handling outputs

Add a guide which highlights how to handle action's outputs by writing
them to the client filesystem and using CUE's integrations to marshal
them as JSON.

Signed-off-by: Marcos Lilljedahl <marcosnils@gmail.com>

docs/guides/1227-contributing.md

@@ -1,6 +1,6 @@
 ---
 slug: /1227/contributing
-displayed_sidebar: europa
+displayed_sidebar: 0.2
 ---
 
 # Contributing to Dagger

docs/guides/1228-handling-outputs.md

@@ -0,0 +1,28 @@
+---
+slug: /1226/handling-outputs
+displayed_sidebar: 0.2
+---
+
+# Handling action outputs
+
+It's most likely that upon executing a Dagger action, you'll find in the situation of having to parse some outputs. In Dagger 0.1 (pre-Europa), inputs and outputs had to be specifically defined; starting Dagger 0.2 (Europa) we introduced a brand new API which removed this capability temporarily until we come up with the [right UX](https://github.com/dagger/dagger/issues/1351) to bring this back. Until the API is ready, you can follow this guide which shows different **temporary** alternatives of parsing dagger outputs.
+
+## Writing outputs to the filesystem
+
+As showcased in the [interacting with the client](/1203/client) docs, Dagger already has the ability to write into the client filesystem through the `client` API. Using this capability we can then output any value into our local filesystem for further automation.
+
+Here's a simple example of a plain text output:
+
+```cue file=../tests/core-concepts/client/plans/output_simple.cue.fragment
+```
+
+After performing `dagger do test`, a new file named `output.txt` will be present in the current working directory with the output of the `bash.#Run` action.
+
+## Marshalling multiple outputs
+
+The above example works well for simple outputs, but most of the time some actions like [Netlify's](https://github.com/dagger/dagger/blob/main/pkg/universe.dagger.io/netlify/netlify.cue) can output mutiple values. In this case, Netlify's action is returning the deployment `url`, `deployUrl` and `logsUrl`. On this case, we can leverage on CUE's [default integrations](https://cuelang.org/docs/integrations/) and marshal all the values into a single `json` or `yaml` file.
+
+Here's an example on how to marshal multiple output values:
+
+```cue file=../tests/core-concepts/client/plans/output_marshal.cue.fragment
+```

docs/tests/core-concepts/client/plans/output_marshal.cue.fragment

@@ -0,0 +1,18 @@
+#SomeAction: {
+	// Nop to make dagger run the action
+	core.#Nop & {}
+	url:       "test.com"
+	deployUrl: "test.com/deploy"
+	logsUrl:   "test.com/logs"
+}
+
+dagger.#Plan & {
+	client: filesystem: "output.json": write: contents: json.Marshal({
+		url:       actions.test.url
+		deployUrl: actions.test.deployUrl
+		logsUrl:   actions.test.logsUrl
+	})
+	actions: {
+		test: #SomeAction & {}
+	}
+}

docs/tests/core-concepts/client/plans/output_simple.cue.fragment

@@ -0,0 +1,15 @@
+dagger.#Plan & {
+	client: filesystem: "output.txt": write: contents: actions.test.export.files["/hello.txt"]
+
+	actions: {
+		_image: alpine.#Build & {
+			packages: bash: {}
+		}
+		test: bash.#Run & {
+			input: _image.output
+			script: contents: "echo Hello World! > /hello.txt"
+			export: files: "/hello.txt": string
+		}
+
+	}
+}

website/sidebars.js

@@ -53,6 +53,8 @@ module.exports = {
         "guides/custom-buildkit",
         "guides/self-signed-certificates",
         "guides/pushing-plan-dependencies",
+        "guides/coding-style",
+	"guides/handling-outputs",
       ],
     },
     {