feat: allow defining the default text output in template

the previous #22243 did not even work as the output.text is not defined
when mounting the component. but this fixes that and also allows to
define the default output text for scaffolder template.

Signed-off-by: Heikki Hellgren <heikki.hellgren@op.fi>

.changeset/forty-cars-scream.md

@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-scaffolder-react': patch
+---
+
+Allow defining default output text to be shown

plugins/scaffolder-react/api-report.md

@@ -277,6 +277,7 @@ export type ScaffolderOutputText = {
   title?: string;
   icon?: string;
   content?: string;
+  default?: boolean;
 };
 
 // @public

plugins/scaffolder-react/src/api/types.ts

@@ -89,6 +89,7 @@ export type ScaffolderOutputText = {
   title?: string;
   icon?: string;
   content?: string;
+  default?: boolean;
 };
 
 /** @public */

plugins/scaffolder-react/src/next/components/TemplateOutputs/DefaultTemplateOutputs.tsx

@@ -14,9 +14,12 @@
  * limitations under the License.
  */
 import { InfoCard, MarkdownContent } from '@backstage/core-components';
-import { ScaffolderTaskOutput } from '@backstage/plugin-scaffolder-react';
+import {
+  ScaffolderOutputText,
+  ScaffolderTaskOutput,
+} from '@backstage/plugin-scaffolder-react';
 import { Box, Paper } from '@material-ui/core';
-import React, { useMemo, useState } from 'react';
+import React, { useEffect, useMemo, useState } from 'react';
 import { LinkOutputs } from './LinkOutputs';
 import { TextOutputs } from './TextOutputs';
 
@@ -30,9 +33,18 @@ export const DefaultTemplateOutputs = (props: {
 }) => {
   const { output } = props;
   const [textOutputIndex, setTextOutputIndex] = useState<number | undefined>(
-    output?.text?.length ? 0 : undefined,
+    undefined,
   );
 
+  useEffect(() => {
+    if (textOutputIndex === undefined && output?.text) {
+      const defaultIndex = output.text.findIndex(
+        (t: ScaffolderOutputText) => t.default,
+      );
+      setTextOutputIndex(defaultIndex >= 0 ? defaultIndex : 0);
+    }
+  }, [textOutputIndex, output]);
+
   const textOutput = useMemo(
     () =>
       textOutputIndex !== undefined ? output?.text?.[textOutputIndex] : null,