Use findfile to simplify recursive file finding

autoload/vimtex.vim

@@ -460,8 +460,8 @@ function! s:init_local_blob() " {{{1
     let l:local.tex = l:filename
     let l:local.pid = 0
     let l:local.name = fnamemodify(l:filename, ':t:r')
-    let l:local.root = fnamemodify(l:filename, ':h')
-    let l:local.base = fnamemodify(l:filename, ':t')
+    let l:local.root = get(s:, 'root', fnamemodify(l:filename, ':h'))
+    let l:local.base = get(s:, 'base', fnamemodify(l:filename, ':t'))
 
     let s:vimtex_next_id += 1
     let g:vimtex_data[s:vimtex_next_id] = l:local
@@ -519,8 +519,7 @@ function! s:get_main() " {{{1
   " Search for TEX root specifier at the beginning of file. This is used by
   " several other plugins and editors.
   "
-  let l:candidate = s:get_main_from_specifier(
-        \ '^\c\s*%\s*!\?\s*tex\s\+root\s*=\s*\zs.*\ze\s*$')
+  let l:candidate = s:get_main_from_texroot()
   if !empty(l:candidate)
     return l:candidate
   endif
@@ -528,8 +527,7 @@ function! s:get_main() " {{{1
   "
   " Support for subfiles package
   "
-  let l:candidate = s:get_main_from_specifier(
-        \ '^\C\s*\\documentclass\[\zs.*\ze\]{subfiles}')
+  let l:candidate = s:get_main_from_subfile()
   if !empty(l:candidate)
     return l:candidate
   endif
@@ -570,21 +568,47 @@ function! s:get_main() " {{{1
 endfunction
 
 " }}}1
-function! s:get_main_from_specifier(spec) " {{{1
+function! s:get_main_from_texroot() " {{{1
   for l:line in getline(1, 5)
-    let l:filename = matchstr(l:line, a:spec)
+    let l:filename = matchstr(l:line,
+          \ '^\c\s*%\s*!\?\s*tex\s\+root\s*=\s*\zs.*\ze\s*$')
     if len(l:filename) > 0
       if l:filename[0] ==# '/'
         if filereadable(l:filename) | return l:filename | endif
       else
-        " The candidate may be relative both to the current buffer file and to
-        " the working directory (for subfile package)
-        for l:candidate in map([
-              \   expand('%:p:h'),
-              \   getcwd()],
-              \ 'simplify(v:val . ''/'' . l:filename)')
-          if filereadable(l:candidate) | return l:candidate | endif
-        endfor
+        let l:candidate = simplify(expand('%:p:h') . '/' . l:filename)
+        if filereadable(l:candidate) | return l:candidate | endif
+      endif
+    endif
+  endfor
+
+  return ''
+endfunction
+
+" }}}1
+function! s:get_main_from_subfile() " {{{1
+  for l:line in getline(1, 5)
+    let l:filename = matchstr(l:line,
+          \ '^\C\s*\\documentclass\[\zs.*\ze\]{subfiles}')
+    if len(l:filename) > 0
+      if l:filename[0] ==# '/'
+        " Specified path is absolute
+        if filereadable(l:filename) | return l:filename | endif
+      else
+        " Try specified path as relative to current file path
+        let l:candidate = simplify(expand('%:p:h') . '/' . l:filename)
+        if filereadable(l:candidate) | return l:candidate | endif
+
+        " Try specified path as relative to the project main file. This is
+        " difficult, since the main file is the one we are looking for. We
+        " therefore assume that the main file lives somewhere upwards in the
+        " directory tree.
+        let l:candidate = findfile(l:filename, '.;')
+        if filereadable(l:candidate)
+          let s:root = fnamemodify(l:candidate, ':h')
+          let s:base = strpart(expand('%:p'), len(s:root) + 1)
+          return l:candidate
+        endif
       endif
     endif
   endfor

test/issues/630/localpackage.sty

@@ -0,0 +1,2 @@
+\ProvidesPackage{localpackage}
+\endinput

test/issues/630/main.tex

@@ -0,0 +1,10 @@
+\documentclass{article}
+\usepackage{filecontents}
+\usepackage{subfiles}
+\usepackage{localpackage}
+
+\begin{document}
+\subfile{sub/sub.tex}
+
+b
+\end{document}

test/issues/630/minivimrc

@@ -0,0 +1,17 @@
+set nocompatible
+let &rtp  = '~/.vim/bundle/vimtex,' . &rtp
+let &rtp .= ',~/.vim/bundle/vimtex/after'
+filetype plugin indent on
+syntax enable
+
+let g:tex_flavor = "latex"
+let g:vimtex_latexmk_background = 1
+
+let g:vimtex_view_general_viewer = 'SumatraPDF'
+let g:vimtex_view_general_options =
+      \ '-reuse-instance -forward-search @line @pdf @tex'
+let g:vimtex_view_general_options_latexmk = '-reuse-instance'
+
+if !has('win32')
+  echoerr 'This test case should be run on windows!'
+endif

test/issues/630/sub/sub.tex

@@ -0,0 +1,5 @@
+\documentclass[main.tex]{subfiles}
+
+\begin{document}
+a
+\end{document}