feat(template): add `lowercase` Handlebars helper (#15212)

docs/usage/templates.md

@@ -58,6 +58,12 @@ In the example above all matches of `github.com` will be replaced by `ghc` in `d
 
 Read the [MDN Web Docs, String.prototype.replace()](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/replace) to learn more.
 
+### lowercase
+
+The `lowercase` helper converts a given string to lower case.
+
+`{{{ lowercase depName }}}`
+
 ### containsString
 
 Returns `true` if a given string is a substring.

lib/util/template/index.spec.ts

@@ -74,4 +74,10 @@ describe('util/template/index', () => {
     const output = template.compile(userTemplate, undefined);
     expect(output).toMatchSnapshot();
   });
+
+  it('lowercase', () => {
+    const userTemplate = "{{{ lowercase 'FOO'}}}";
+    const output = template.compile(userTemplate, undefined);
+    expect(output).toBe('foo');
+  });
 });

lib/util/template/index.ts

@@ -17,6 +17,8 @@ handlebars.registerHelper(
     (context || '').replace(new RegExp(find, 'g'), replace) // TODO #12873
 );
 
+handlebars.registerHelper('lowercase', (str: string) => str.toLowerCase());
+
 handlebars.registerHelper('containsString', (str, subStr, options) =>
   str.includes(subStr)
 );