patch 8.0.1781: file names in quickfix window are not shortened

Problem:    File names in quickfix window are not always shortened.
Solution:   Shorten the file name when opening the quickfix window. (Yegappan
            Lakshmanan, closes #2851, closes #2846)
diff --git a/src/fileio.c b/src/fileio.c
index 63cc61c..98631e0 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -6163,7 +6163,7 @@
 }
 
 /*
- * Shorten filenames for all buffers.
+ * Shorten filename of a buffer.
  * When "force" is TRUE: Use full path from now on for files currently being
  * edited, both for file name and swap file name.  Try to shorten the file
  * names a bit, if safe to do so.
@@ -6172,34 +6172,44 @@
  * name.
  */
     void
+shorten_buf_fname(buf_T *buf, char_u *dirname, int force)
+{
+    char_u	*p;
+
+    if (buf->b_fname != NULL
+#ifdef FEAT_QUICKFIX
+	    && !bt_nofile(buf)
+#endif
+	    && !path_with_url(buf->b_fname)
+	    && (force
+		|| buf->b_sfname == NULL
+		|| mch_isFullName(buf->b_sfname)))
+    {
+	VIM_CLEAR(buf->b_sfname);
+	p = shorten_fname(buf->b_ffname, dirname);
+	if (p != NULL)
+	{
+	    buf->b_sfname = vim_strsave(p);
+	    buf->b_fname = buf->b_sfname;
+	}
+	if (p == NULL || buf->b_fname == NULL)
+	    buf->b_fname = buf->b_ffname;
+    }
+}
+
+/*
+ * Shorten filenames for all buffers.
+ */
+    void
 shorten_fnames(int force)
 {
     char_u	dirname[MAXPATHL];
     buf_T	*buf;
-    char_u	*p;
 
     mch_dirname(dirname, MAXPATHL);
     FOR_ALL_BUFFERS(buf)
     {
-	if (buf->b_fname != NULL
-#ifdef FEAT_QUICKFIX
-		&& !bt_nofile(buf)
-#endif
-		&& !path_with_url(buf->b_fname)
-		&& (force
-		    || buf->b_sfname == NULL
-		    || mch_isFullName(buf->b_sfname)))
-	{
-	    VIM_CLEAR(buf->b_sfname);
-	    p = shorten_fname(buf->b_ffname, dirname);
-	    if (p != NULL)
-	    {
-		buf->b_sfname = vim_strsave(p);
-		buf->b_fname = buf->b_sfname;
-	    }
-	    if (p == NULL || buf->b_fname == NULL)
-		buf->b_fname = buf->b_ffname;
-	}
+	shorten_buf_fname(buf, dirname, force);
 
 	/* Always make the swap file name a full path, a "nofile" buffer may
 	 * also have a swap file. */
diff --git a/src/proto/fileio.pro b/src/proto/fileio.pro
index 12d5c14..9903481 100644
--- a/src/proto/fileio.pro
+++ b/src/proto/fileio.pro
@@ -11,6 +11,7 @@
 void msg_add_lines(int insert_space, long lnum, off_T nchars);
 char_u *shorten_fname1(char_u *full_path);
 char_u *shorten_fname(char_u *full_path, char_u *dir_name);
+void shorten_buf_fname(buf_T *buf, char_u *dirname, int force);
 void shorten_fnames(int force);
 void shorten_filenames(char_u **fnames, int count);
 char_u *modname(char_u *fname, char_u *ext, int prepend_dot);
diff --git a/src/quickfix.c b/src/quickfix.c
index acff1ec..dde6841 100644
--- a/src/quickfix.c
+++ b/src/quickfix.c
@@ -2736,6 +2736,9 @@
 	    idx2 = (-idx2 > i) ? 0 : idx2 + i + 1;
     }
 
+    /* Shorten all the file names, so that it is easy to read */
+    shorten_fnames(FALSE);
+
     /*
      * Get the attributes for the different quickfix highlight items.  Note
      * that this depends on syntax items defined in the qf.vim syntax file
@@ -3542,6 +3545,10 @@
     /* Check if there is anything to display */
     if (qi->qf_curlist < qi->qf_listcount)
     {
+	char_u	dirname[MAXPATHL];
+
+	*dirname = NUL;
+
 	/* Add one line for each error */
 	if (old_last == NULL)
 	{
@@ -3562,7 +3569,17 @@
 		if (qfp->qf_type == 1)	/* :helpgrep */
 		    STRCPY(IObuff, gettail(errbuf->b_fname));
 		else
+		{
+		    /* shorten the file name if not done already */
+		    if (errbuf->b_sfname == NULL
+					   || mch_isFullName(errbuf->b_sfname))
+		    {
+			if (*dirname == NUL)
+			    mch_dirname(dirname, MAXPATHL);
+			shorten_buf_fname(errbuf, dirname, FALSE);
+		    }
 		    STRCPY(IObuff, errbuf->b_fname);
+		}
 		len = (int)STRLEN(IObuff);
 	    }
 	    else
diff --git a/src/testdir/test_quickfix.vim b/src/testdir/test_quickfix.vim
index 092a5c4..1e781de 100644
--- a/src/testdir/test_quickfix.vim
+++ b/src/testdir/test_quickfix.vim
@@ -3201,3 +3201,27 @@
   au! QuickFixCmdPost
   new | only
 endfunc
+
+" Test for shortening/simplifying the file name when opening the
+" quickfix window or when displaying the quickfix list
+func Test_shorten_fname()
+  if !has('unix')
+    return
+  endif
+  %bwipe
+  " Create a quickfix list with a absolute path filename
+  let fname = getcwd() . '/test_quickfix.vim'
+  call setqflist([], ' ', {'lines':[fname . ":20:Line20"], 'efm':'%f:%l:%m'})
+  call assert_equal(fname, bufname('test_quickfix.vim'))
+  " Opening the quickfix window should simplify the file path
+  cwindow
+  call assert_equal('test_quickfix.vim', bufname('test_quickfix.vim'))
+  cclose
+  %bwipe
+  " Create a quickfix list with a absolute path filename
+  call setqflist([], ' ', {'lines':[fname . ":20:Line20"], 'efm':'%f:%l:%m'})
+  call assert_equal(fname, bufname('test_quickfix.vim'))
+  " Displaying the quickfix list should simplify the file path
+  silent! clist
+  call assert_equal('test_quickfix.vim', bufname('test_quickfix.vim'))
+endfunc
diff --git a/src/version.c b/src/version.c
index 7726f84..ae231be 100644
--- a/src/version.c
+++ b/src/version.c
@@ -762,6 +762,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1781,
+/**/
     1780,
 /**/
     1779,