feat(rust): insert docblock above macros

autoload/doge/preprocessors/javascript.vim

@@ -3,7 +3,7 @@ set cpoptions&vim
 
 " Alter the insert position for JavaScript functions.
 function! doge#preprocessors#javascript#insert_position(lnum_insert_pos) abort
-  " In Java some functions may have the ES7 decorators above them.
+  " In Java, some functions may have the ES7 decorators above them.
   " If this is the case we want to insert above this.
   "
   " Example:

autoload/doge/preprocessors/rust.vim

@@ -0,0 +1,38 @@
+let s:save_cpo = &cpoptions
+set cpoptions&vim
+
+" Alter the insert position for JavaScript functions.
+function! doge#preprocessors#rust#insert_position(lnum_insert_pos) abort
+  " In Rust, some functions may have #[...] macros above them.
+  " If this is the case we want to insert above this.
+  "
+  " Example:
+  "   #[doc(alias = "x")]
+  "   #[doc(alias = "big")]
+  "   pub struct BigX;
+
+  " Go to the beginning of the line.
+  call execute('normal! ^')
+
+  let l:offset = 1
+  let l:has_macros = 0
+  while doge#helpers#trim(getline(line('.') - l:offset)) =~# '\m^#['
+
+    " Assume that a user won't have more than 20 macros on a function.
+    " When we reach 20 lines or more, return and do nothing.
+    if l:offset > 20
+      return a:lnum_insert_pos
+    endif
+
+    let l:has_macros = 1
+    let l:offset += 1
+
+  endwhile
+
+  return l:has_macros == v:true
+        \ ? a:lnum_insert_pos - l:offset + 1
+        \ : a:lnum_insert_pos
+endfunction
+
+let &cpoptions = s:save_cpo
+unlet s:save_cpo

test/filetypes/rust/functions.vader

@@ -63,9 +63,11 @@ Expect rust (generated comments with Arguments and Examples sections):
 # Functions with errors and safety section
 # ==============================================================================
 Given rust (impl methods with Errors and Safety section):
+  #[macro_export]
   pub unsafe fn foo(foo: usize) -> Result<(), FooError> {}
 
 Do (trigger doge):
+  :2\<CR>
   \<C-d>
 
 Expect rust (generated comments with Arguments, Safety, Errors and Examples sections):
@@ -88,4 +90,5 @@ Expect rust (generated comments with Arguments, Safety, Errors and Examples sect
   /// ```
   /// [TODO:example]
   /// ```
+  #[macro_export]
   pub unsafe fn foo(foo: usize) -> Result<(), FooError> {}