Change the per-project option file to be .gutctags and process it f…

…irst.

When using Gutentags with a cache directory put all the tag files in, the
`ctags` executable will be run against absolute paths, because the output paths
in the tag file will also need to be absolute in order to make it possible to
open them in an editor. This means exclude rules need to be run against
absolute paths too, so we make those rules absolute and store the result in a
temporary file that we pass to `ctags` as the real options file.

autoload/gutentags/ctags.vim

@@ -14,6 +14,10 @@ if !exists('g:gutentags_auto_set_tags')
     let g:gutentags_auto_set_tags = 1
 endif
 
+if !exists('g:gutentags_ctags_options_file')
+    let g:gutentags_ctags_options_file = '.gutctags'
+endif
+
 " }}}
 
 " Gutentags Module Interface {{{
@@ -57,8 +61,11 @@ function! gutentags#ctags#generate(proj_dir, tags_file, write_mode) abort
         if g:gutentags_pause_after_update
             let l:cmd .= ' -c'
         endif
-        let l:proj_options_file = a:proj_dir . '/.ctags'
+        let l:proj_options_file = a:proj_dir . '/' . 
+                    \g:gutentags_ctags_options_file
         if filereadable(l:proj_options_file)
+            let l:proj_options_file = s:process_options_file(
+                        \a:proj_dir, l:proj_options_file)
             let l:cmd .= ' -o "' . l:proj_options_file . '"'
         endif
         if g:gutentags_trace
@@ -99,3 +106,58 @@ endfunction
 
 " }}}
 
+" Utilities {{{
+
+function! s:process_options_file(proj_dir, path) abort
+    if g:gutentags_cache_dir == ""
+        " If we're not using a cache directory to store tag files, we can
+        " use the options file straight away.
+        return a:path
+    endif
+
+    " See if we need to process the options file.
+    let l:do_process = 0
+    let l:proj_dir = gutentags#stripslash(a:proj_dir)
+    let l:out_path = gutentags#get_cachefile(l:proj_dir, 'options')
+    if !filereadable(l:out_path)
+        call gutentags#trace("Processing options file '".a:path."' because ".
+                    \"it hasn't been processed yet.")
+        let l:do_process = 1
+    elseif getftime(a:path) > getftime(l:out_path)
+        call gutentags#trace("Processing options file '".a:path."' because ".
+                    \"it has changed.")
+        let l:do_process = 1
+    endif
+    if l:do_process == 0
+        " Nothing's changed, return the existing processed version of the
+        " options file.
+        return l:out_path
+    endif
+
+    " We have to process the options file. Right now this only means capturing
+    " all the 'exclude' rules, and rewrite them to make them absolute.
+    "
+    " This is because since `ctags` is run with absolute paths (because we
+    " want the tag file to be in a cache directory), it will do its path
+    " matching with absolute paths too, so the exclude rules need to be
+    " absolute.
+    let l:lines = readfile(a:path)
+    let l:outlines = []
+    for line in l:lines
+        let l:exarg = matchend(line, '\v^\-\-exclude=')
+        if l:exarg < 0
+            call add(l:outlines, line)
+            continue
+        endif
+        let l:fullp = gutentags#normalizepath(l:proj_dir.'/'.
+                    \strpart(line, l:exarg + 1))
+        let l:ol = '--exclude='.l:fullp
+        call add(l:outlines, l:ol)
+    endfor
+
+    call writefile(l:outlines, l:out_path)
+    return l:out_path
+endfunction
+
+" }}}
+