feat: add stringToPrettyJSON handlebars function (#12643)

docs/usage/templates.md

@@ -20,3 +20,13 @@ Some are configuration options passed through, while others are generated as par
 ## Other available fields
 
 <!-- Insert runtime fields here -->
+
+## Additional Handlebars helpers
+
+### stringToPrettyJSON
+
+If you want to print pretty JSON with Handlebars you can use the built-in function `stringToPrettyJSON` like this:
+
+`{{{stringToPrettyJSON myvar}}}`
+
+In the example above `myvar` is a variable/field, that contains valid JSON.

lib/util/template/__snapshots__/index.spec.ts.snap

 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
 exports[`util/template/index filters out disallowed fields 1`] = `"github token = \\"\\""`;
+
+exports[`util/template/index string to pretty JSON  1`] = `
+"{
+  \\"some\\": {
+    \\"fancy\\": \\"json\\"
+  }
+}"
+`;

lib/util/template/index.spec.ts

@@ -18,4 +18,10 @@ describe('util/template/index', () => {
     expect(output).toContain('github');
     expect(output).not.toContain('123test');
   });
+  it('string to pretty JSON ', () => {
+    const userTemplate =
+      '{{{ stringToPrettyJSON \'{"some":{"fancy":"json"}}\'}}}';
+    const output = template.compile(userTemplate, undefined);
+    expect(output).toMatchSnapshot();
+  });
 });

lib/util/template/index.ts

@@ -6,6 +6,10 @@ import { clone } from '../clone';
 
 handlebars.registerHelper('encodeURIComponent', encodeURIComponent);
 
+handlebars.registerHelper('stringToPrettyJSON', (input: string): string =>
+  JSON.stringify(JSON.parse(input), null, 2)
+);
+
 // istanbul ignore next
 handlebars.registerHelper(
   'replace',