Convert indented partial results to a string before splitting

Rendering an indented partial that resolves through @partial-block
crashes with "result.split is not a function" whenever a helper along
the way hands back something other than a plain string, a SafeString
being the common case. This happens with both a real partial-block
and an inline partial, since the indentation code always assumes it's
holding a string once options.indent is set.

Fixes #1695. A prior attempt at this fix
(#1916) went stale without ever getting reviewed; the change here is
the same one-line idea, just reapplied against master with a couple
of regression tests covering both the partial-block and inline-partial
cases from the original report.

Author: afonsojanu

lib/handlebars/runtime.js

@@ -86,6 +86,10 @@ export function template(templateSpec, env) {
     }
     if (result != null) {
       if (options.indent) {
+        // a helper invoked through the partial-block (e.g. one wrapping its
+        // output in a SafeString) can hand back something other than a
+        // plain string here, and that breaks the split() below
+        result = '' + result;
         let lines = result.split('\n');
         for (let i = 0, l = lines.length; i < l; i++) {
           if (!lines[i] && i + 1 === l) {

spec/partials.js

@@ -604,6 +604,25 @@ describe('partials', function () {
           'Dudes:\n  Yehuda\n http://yehuda!\n  Alan\n http://alan!\n'
         );
     });
+
+    it('indented partial-block whose content is a SafeString (GH-1695)', function () {
+      expectTemplate('{{#>myPartial}}{{#safe}}success{{/safe}}{{/myPartial}}')
+        .withHelper('safe', function (options) {
+          return new Handlebars.SafeString(options.fn(this));
+        })
+        .withPartial('myPartial', '  {{> @partial-block }}')
+        .toCompileTo('  success');
+    });
+
+    it('indented inline partial whose content is a SafeString (GH-1695)', function () {
+      expectTemplate(
+        '{{#*inline "myPartial"}}{{#safe}}success{{/safe}}{{/inline}}\n  {{> myPartial}}'
+      )
+        .withHelper('safe', function (options) {
+          return new Handlebars.SafeString(options.fn(this));
+        })
+        .toCompileTo('\n  success');
+    });
   });
 
   describe('compat mode', function () {