patch 9.1.0558: filetype: prolog detection can be improved

Problem:  filetype: prolog detection can be improved
Solution: Improved the Prolog file detection regex and added tests for
          all cases. (igna_martinoli)

fixes: #10835
closes: #15206

Signed-off-by: igna_martinoli <ignamartinoli@protonmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/autoload/dist/ft.vim

@@ -465,7 +465,7 @@ export def ProtoCheck(default: string)
     # recognize Prolog by specific text in the first non-empty line
     # require a blank after the '%' because Perl uses "%list" and "%translate"
     var lnum = getline(nextnonblank(1))
-    if lnum =~ '\<prolog\>' || lnum =~ '^\s*\(%\+\(\s\|$\)\|/\*\)' || lnum =~ ':-'
+    if lnum =~ '\<prolog\>' || lnum =~ '(^\s*(:-\|%\|\/\*))\|.\s*$'
       setf prolog
     else
       exe 'setf ' .. default

src/testdir/test_filetype.vim

@@ -2576,4 +2576,31 @@ func Test_uci_file()
   filetype off
 endfunc
 
+func Test_pro_file()
+  filetype on
+
+  "Prolog
+  call writefile([':-module(test/1,'], 'Xfile.pro', 'D')
+  split Xfile.pro
+  call assert_equal('prolog', &filetype)
+  bwipe!
+
+  call writefile(['% comment'], 'Xfile.pro', 'D')
+  split Xfile.pro
+  call assert_equal('prolog', &filetype)
+  bwipe!
+
+  call writefile(['/* multiline comment'], 'Xfile.pro', 'D')
+  split Xfile.pro
+  call assert_equal('prolog', &filetype)
+  bwipe!
+
+  call writefile(['rule(test, 1.7).'], 'Xfile.pro', 'D')
+  split Xfile.pro
+  call assert_equal('prolog', &filetype)
+  bwipe!
+
+  filetype off
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab

src/version.c

@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    558,
 /**/
     557,
 /**/