ENHANCEMENT Allow <% include %> to fallback outside of the Includes folder

Fixes #7108

src/View/SSTemplateParser.peg

@@ -891,7 +891,7 @@ class SSTemplateParser extends Parser implements TemplateParser
         $template = $res['template'];
         $arguments = $res['arguments'];
 
-        $res['php'] = '$val .= \\SilverStripe\\View\\SSViewer::execute_template(["type" => "Includes", '.$template.'], $scope->getItem(), array(' .
+        $res['php'] = '$val .= \\SilverStripe\\View\\SSViewer::execute_template([["type" => "Includes", '.$template.'], '.$template.'], $scope->getItem(), array(' .
             implode(',', $arguments)."), \$scope);\n";
 
         if ($this->includeDebuggingComments) { // Add include filename comments on dev sites

src/View/SSTemplateParser.php

@@ -3499,7 +3499,7 @@ class SSTemplateParser extends Parser implements TemplateParser
         $template = $res['template'];
         $arguments = $res['arguments'];
 
-        $res['php'] = '$val .= \\SilverStripe\\View\\SSViewer::execute_template(["type" => "Includes", '.$template.'], $scope->getItem(), array(' .
+        $res['php'] = '$val .= \\SilverStripe\\View\\SSViewer::execute_template([["type" => "Includes", '.$template.'], '.$template.'], $scope->getItem(), array(' .
             implode(',', $arguments)."), \$scope);\n";
 
         if ($this->includeDebuggingComments) { // Add include filename comments on dev sites

tests/php/View/SSViewerTest.php

@@ -1055,6 +1055,12 @@ after'
             'Backslashes work for namespace references in includes'
         );
 
+        $this->assertEquals(
+            "tests:( NamespaceInclude\n )",
+            $this->render('tests:( <% include Namespace\\NamespaceInclude %> )', $data),
+            'Escaped backslashes work for namespace references in includes'
+        );
+
         $this->assertEquals(
             "tests:( NamespaceInclude\n )",
             $this->render('tests:( <% include Namespace/NamespaceInclude %> )', $data),
@@ -1062,6 +1068,31 @@ after'
         );
     }
 
+    /**
+     * Test search for includes fallback to non-includes folder
+     */
+    public function testIncludeFallbacks()
+    {
+        $data = new ArrayData([]);
+
+        $this->assertEquals(
+            "tests:( Namespace/Includes/IncludedTwice.ss\n )",
+            $this->render('tests:( <% include Namespace\\IncludedTwice %> )', $data),
+            'Prefer Includes in the Includes folder'
+        );
+
+        $this->assertEquals(
+            "tests:( Namespace/Includes/IncludedOnceSub.ss\n )",
+            $this->render('tests:( <% include Namespace\\IncludedOnceSub %> )', $data),
+            'Includes in only Includes folder can be found'
+        );
+
+        $this->assertEquals(
+            "tests:( Namespace/IncludedOnceBase.ss\n )",
+            $this->render('tests:( <% include Namespace\\IncludedOnceBase %> )', $data),
+            'Includes outside of Includes folder can be found'
+        );
+    }
 
     public function testRecursiveInclude()
     {

tests/php/View/SSViewerTest/templates/Namespace/IncludedOnceBase.ss

@@ -0,0 +1 @@
+Namespace/IncludedOnceBase.ss

tests/php/View/SSViewerTest/templates/Namespace/IncludedTwice.ss

@@ -0,0 +1 @@
+Namespace/IncludedTwice.ss

tests/php/View/SSViewerTest/templates/Namespace/Includes/IncludedOnceSub.ss

@@ -0,0 +1 @@
+Namespace/Includes/IncludedOnceSub.ss

tests/php/View/SSViewerTest/templates/Namespace/Includes/IncludedTwice.ss

@@ -0,0 +1 @@
+Namespace/Includes/IncludedTwice.ss