vim-patch:8.2.0077: settagstack() cannot truncate at current index

Problem:    settagstack() cannot truncate at current index.
Solution:   Add the "t" action. (Yegappan Lakshmanan, closes vim/vim#5417)
271fa08a35

src/nvim/eval.c

@@ -16242,7 +16242,8 @@ static void f_settagstack(typval_T *argvars, typval_T *rettv, FunPtr fptr)
         if (actstr == NULL) {
           return;
         }
-        if ((*actstr == 'r' || *actstr == 'a') && actstr[1] == NUL) {
+        if ((*actstr == 'r' || *actstr == 'a' || *actstr == 't')
+            && actstr[1] == NUL) {
           action = *actstr;
         } else {
             EMSG2(_(e_invact2), actstr);

src/nvim/tag.c

@@ -3378,11 +3378,15 @@ static void tagstack_set_curidx(win_T *wp, int curidx)
 }
 
 // Set the tag stack entries of the specified window.
-// 'action' is set to either 'a' for append or 'r' for replace.
-int set_tagstack(win_T *wp, dict_T *d, int action)
+// 'action' is set to one of:
+//    'a' for append
+//    'r' for replace
+//    't' for truncate
+int set_tagstack(win_T *wp, const dict_T *d, int action)
+  FUNC_ATTR_NONNULL_ARG(1)
 {
   dictitem_T *di;
-  list_T *l;
+  list_T *l = NULL;
 
   // not allowed to alter the tag stack entries from inside tagfunc
   if (tfu_in_use) {
@@ -3395,17 +3399,31 @@ int set_tagstack(win_T *wp, dict_T *d, int action)
       return FAIL;
     }
     l = di->di_tv.vval.v_list;
-
-    if (action == 'r') {
-      tagstack_clear(wp);
-    }
-
-    tagstack_push_items(wp, l);
   }
 
   if ((di = tv_dict_find(d, "curidx", -1)) != NULL) {
     tagstack_set_curidx(wp, (int)tv_get_number(&di->di_tv) - 1);
   }
+  if (action == 't') {  // truncate the stack
+    taggy_T *const tagstack = wp->w_tagstack;
+    const int tagstackidx = wp->w_tagstackidx;
+    int tagstacklen = wp->w_tagstacklen;
+    // delete all the tag stack entries above the current entry
+    while (tagstackidx < tagstacklen) {
+      tagstack_clear_entry(&tagstack[--tagstacklen]);
+    }
+    wp->w_tagstacklen = tagstacklen;
+  }
+
+  if (l != NULL) {
+    if (action == 'r') {  // replace the stack
+      tagstack_clear(wp);
+    }
+
+    tagstack_push_items(wp, l);
+    // set the current index after the last entry
+    wp->w_tagstackidx = wp->w_tagstacklen;
+  }
 
   return OK;
 }

src/nvim/testdir/test_tagjump.vim

@@ -340,6 +340,28 @@ func Test_getsettagstack()
         \ {'items' : [{'tagname' : 'abc', 'from' : [1, 10, 1, 0]}]}, 'a')
   call assert_equal('abc', gettagstack().items[19].tagname)
 
+  " truncate the tag stack
+  call settagstack(1,
+        \ {'curidx' : 9,
+        \  'items' : [{'tagname' : 'abc', 'from' : [1, 10, 1, 0]}]}, 't')
+  let t = gettagstack()
+  call assert_equal(9, t.length)
+  call assert_equal(10, t.curidx)
+
+  " truncate the tag stack without pushing any new items
+  call settagstack(1, {'curidx' : 5}, 't')
+  let t = gettagstack()
+  call assert_equal(4, t.length)
+  call assert_equal(5, t.curidx)
+
+  " truncate an empty tag stack and push new items
+  call settagstack(1, {'items' : []})
+  call settagstack(1,
+        \ {'items' : [{'tagname' : 'abc', 'from' : [1, 10, 1, 0]}]}, 't')
+  let t = gettagstack()
+  call assert_equal(1, t.length)
+  call assert_equal(2, t.curidx)
+
   " Tag with multiple matches
   call writefile(["!_TAG_FILE_ENCODING\tutf-8\t//",
         \ "two\tXfile1\t1",