patch 8.1.0133: tagfiles() can have duplicate entries

Problem:    tagfiles() can have duplicate entries.
Solution:   Simplify the filename to make checking for duplicates work better.
            Add a test. (Dominique Pelle, closes #2979)

src/tag.c

@@ -2595,7 +2595,6 @@ findtag_end:
 }
 
 static garray_T tag_fnames = GA_EMPTY;
-static void found_tagfile_cb(char_u *fname, void *cookie);
 
 /*
  * Callback function for finding all "tags" and "tags-??" files in
@@ -2605,8 +2604,15 @@ static void found_tagfile_cb(char_u *fname, void *cookie);
 found_tagfile_cb(char_u *fname, void *cookie UNUSED)
 {
     if (ga_grow(&tag_fnames, 1) == OK)
-	((char_u **)(tag_fnames.ga_data))[tag_fnames.ga_len++] =
-							   vim_strsave(fname);
+    {
+	char_u	*tag_fname = vim_strsave(fname);
+
+#ifdef BACKSLASH_IN_FILENAME
+	slash_adjust(tag_fname);
+#endif
+	simplify_filename(tag_fname);
+	((char_u **)(tag_fnames.ga_data))[tag_fnames.ga_len++] = tag_fname;
+    }
 }
 
 #if defined(EXITFREE) || defined(PROTO)
@@ -2638,6 +2644,7 @@ get_tagfname(
 {
     char_u		*fname = NULL;
     char_u		*r_ptr;
+    int			i;
 
     if (first)
 	vim_memset(tnp, 0, sizeof(tagname_T));
@@ -2679,6 +2686,14 @@ get_tagfname(
 	    ++tnp->tn_hf_idx;
 	    STRCPY(buf, p_hf);
 	    STRCPY(gettail(buf), "tags");
+#ifdef BACKSLASH_IN_FILENAME
+	    slash_adjust(buf);
+#endif
+	    simplify_filename(buf);
+
+	    for (i = 0; i < tag_fnames.ga_len; ++i)
+		if (STRCMP(buf, ((char_u **)(tag_fnames.ga_data))[i]) == 0)
+		    return FAIL; // avoid duplicate file names
 	}
 	else
 	    vim_strncpy(buf, ((char_u **)(tag_fnames.ga_data))[

src/testdir/test_taglist.vim

@@ -1,4 +1,4 @@
-" test 'taglist' function and :tags command
+" test taglist(), tagfiles() functions and :tags command
 
 func Test_taglist()
   call writefile([
@@ -61,3 +61,26 @@ func Test_tags_too_long()
   call assert_fails('tag ' . repeat('x', 1020), 'E426')
   tags
 endfunc
+
+func Test_tagfiles()
+  call assert_equal([], tagfiles())
+
+  call writefile(["FFoo\tXfoo\t1"], 'Xtags1')
+  call writefile(["FBar\tXbar\t1"], 'Xtags2')
+  set tags=Xtags1,Xtags2
+  call assert_equal(['Xtags1', 'Xtags2'], tagfiles())
+
+  help
+  let tf = tagfiles()
+  call assert_equal(1, len(tf))
+  call assert_equal(fnamemodify(expand('$VIMRUNTIME/doc/tags'), ':p:gs?\\?/?'),
+	\           fnamemodify(tf[0], ':p:gs?\\?/?'))
+  helpclose
+  call assert_equal(['Xtags1', 'Xtags2'], tagfiles())
+  set tags&
+  call assert_equal([], tagfiles())
+
+  call delete('Xtags1')
+  call delete('Xtags2')
+  bd
+endfunc

src/version.c

@@ -789,6 +789,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    133,
 /**/
     132,
 /**/