Fix cross-linking in whitespace-trimmed files

Signed-off-by: Danila Fedorin <danila.fedorin@gmail.com>

agda.rb

@@ -160,6 +160,14 @@ class FileGroup
         line_range = 1..
       end
 
+      # Sometimes, code is deeply nested in the source file, but we don't
+      # want to show the leading space. In that case, the generator sets
+      # data-source-offset with how much leading space was stripped off.
+      initial_offset = 0
+      if source_offset_attr = t.attribute("data-source-offset")
+        initial_offset = source_offset_attr.to_s.to_i
+      end
+
       full_path = t.attribute("data-file-path").to_s
       full_path_dirs = Pathname(full_path).each_filename.to_a
 
@@ -195,7 +203,7 @@ class FileGroup
         line_info = agda_info[line_no]
         next unless line_info
 
-        offset = 0
+        offset = initial_offset
         line.traverse do |lt|
           if lt.text?
             content = lt.content

themes/vanilla

@@ -1 +1 @@
-Subproject commit 0cdd2fbf6484f994ebacac24020d510be7c56bb2
+Subproject commit 98a9d782730fd714ae7a3300d8cf6791ed0bc341