Use compdb to post-process compile_commands.json

When selecting a `:BuildDir` for the `clangd` LSP use `compdb` to
post-process the `compile_commands.json` to also include flags for
stand alone header files.

.conduit.yaml

@@ -4,6 +4,7 @@
     - vim-vint
     - yamllint
     - cmakelint
+    - compdb
 - repo:
     - remote: https://github.com/k-takata/minpac.git
       location: ~/.vim/pack/minpac/opt/minpac

autoload/build.vim

@@ -28,6 +28,7 @@ function! build#dir(...) abort
         endfor
         let l:index = inputlist(l:choices)
         let l:dir = s:dirs[l:index - 1]
+        echomsg ' '.l:dir
       endif
     endif
   else
@@ -48,17 +49,30 @@ function! build#dir(...) abort
     endif
   endif
   if exists('l:dir')
-    " Set build directory and restart YouCompleteMe.
+    " Set build directory.
-    let $BUILD_DIR = getcwd().'/'.substitute(l:dir, '\/$', '', '')
+    let l:cwd = substitute(getcwd(), '\\', '\/', 'g')
+    let $BUILD_DIR = l:cwd.'/'.substitute(l:dir, '\/$', '', '')
+    if executable('compdb')
+      " Post-process compile_commands.json with compdb, adds header files to
+      " missing compile_commands.json for more accurate diagnostics.
+      let l:database_dir = l:cwd.'/.vim'
+      let l:compile_commands = l:database_dir.'/compile_commands.json'
+      call systemlist('compdb -p '.$BUILD_DIR.' list > '.l:compile_commands)
+    else
+      let l:database_dir = $BUILD_DIR
+    endif
+    " Read/create .vim/coc-settings.json
     let l:coc_settings = {}
     if isdirectory('.vim')
       let l:coc_settings = json_decode(join(readfile('.vim/coc-settings.json'), ''))
     else
       call mkdir('.vim')
     endif
-    let l:coc_settings['clangd.compilationDatabasePath'] = $BUILD_DIR
+    " Update .vim/coc-settings.json with new build directory.
+    let l:coc_settings['clangd.compilationDatabasePath'] = l:database_dir
     let l:coc_settings['cmake.lsp.buildDirectory'] = $BUILD_DIR
     call writefile([json_encode(l:coc_settings)], '.vim/coc-settings.json')
+    " Finally restart coc.nvim with new config.
     CocRestart
   endif
 endfunction