Fix parser translator ast for regex with fake newlines

lib/prism/translation/parser/compiler.rb

@@ -1090,7 +1090,7 @@ def visit_integer_node(node)
         def visit_interpolated_regular_expression_node(node)
           builder.regexp_compose(
             token(node.opening_loc),
-            visit_all(node.parts),
+            string_nodes_from_interpolation(node, node.opening),
             [node.closing[0], srange_offsets(node.closing_loc.start_offset, node.closing_loc.start_offset + 1)],
             builder.regexp_options([node.closing[1..], srange_offsets(node.closing_loc.start_offset + 1, node.closing_loc.end_offset)])
           )
@@ -2109,6 +2109,7 @@ def string_nodes_from_line_continuations(unescaped, escaped, start_offset, openi
           unescaped = unescaped.lines
           escaped = escaped.lines
           percent_array = opening&.start_with?("%w", "%W", "%i", "%I")
+          regex = opening == "/" || opening&.start_with?("%r")
 
           # Non-interpolating strings
           if opening&.end_with?("'") || opening&.start_with?("%q", "%s", "%w", "%i")
@@ -2144,7 +2145,8 @@ def string_nodes_from_line_continuations(unescaped, escaped, start_offset, openi
               .each do |lines|
                 escaped_lengths << lines.sum(&:bytesize)
                 unescaped_lines_count = lines.sum do |line|
-                  line.scan(/(\\*)n/).count { |(backslashes)| backslashes&.length&.odd? || false }
+                  next 0 if regex # Will always be preserved as is
+                  line.scan(/(\\*)n/).count { |(backslashes)| backslashes&.length&.odd?}
                 end
                 extra = 1
                 extra = lines.count if percent_array # Account for line continuations in percent arrays

test/prism/fixtures/regex_with_fake_newlines.txt

@@ -0,0 +1,41 @@
+/
+  \n
+  \n
+  exit
+  \\n
+  \n\n\n\n
+  argh
+  \\
+  \\\
+  foo\nbar
+  \f
+  ok
+/
+
+%r{
+  \n
+  \n
+  exit
+  \\n
+  \n\n\n\n
+  argh
+  \\
+  \\\
+  foo\nbar
+  \f
+  ok
+}
+
+%r{
+  #{123}\n
+  \n
+  exit\\\
+  \\#{123}n
+  \n#{123}\n\n\n
+  argh\
+  \\#{123}baz\\
+  \\\
+  foo\nbar
+  \f
+  ok
+}