vim-patch:9.1.0155: can only get getregion() from current buffer (#27757)

Problem:  can only call getregion() for current buffer
Solution: Allow to retrieve selections from different buffers
          (Shougo Matsushita)

closes: vim/vim#14131

84bf6e658d

Co-authored-by: Shougo Matsushita <Shougo.Matsu@gmail.com>

src/nvim/eval.lua

@@ -4359,11 +4359,13 @@ M.funcs = {
     args = { 2, 3 },
     base = 1,
     desc = [=[
-      Returns the list of strings from {pos1} to {pos2} in current
+      Returns the list of strings from {pos1} to {pos2} from a
       buffer.
 
       {pos1} and {pos2} must both be |List|s with four numbers.
-      See |getpos()| for the format of the list.
+      See |getpos()| for the format of the list.  It's possible
+      to specify positions from a different buffer, but please
+      note the limitations at |getregion-notes|
 
       The optional argument {opts} is a Dict and supports the
       following items:
@@ -4384,6 +4386,7 @@ M.funcs = {
       This function is useful to get text starting and ending in
       different columns, such as a |charwise-visual| selection.
 
+      					*getregion-notes*
       Note that:
       - Order of {pos1} and {pos2} doesn't matter, it will always
         return content from the upper left position to the lower
@@ -4393,8 +4396,12 @@ M.funcs = {
       - If the region is blockwise and it starts or ends in the
         middle of a multi-cell character, it is not included but
         its selected part is substituted with spaces.
-      - If {pos1} or {pos2} is not current in the buffer, an empty
+      - If {pos1} and {pos2} are not in the same buffer, an empty
         list is returned.
+      - {pos1} and {pos2} must belong to a |bufloaded()| buffer.
+      - It is evaluated in current window context, this makes a
+        different if a buffer is displayed in a different window and
+        'virtualedit' or 'list' is set
 
       Examples: >
       	:xnoremap <CR>

src/nvim/eval/funcs.c

@@ -2827,16 +2827,12 @@ static void f_getregion(typval_T *argvars, typval_T *rettv, EvalFuncData fptr)
     return;
   }
 
-  int fnum = -1;
-  pos_T p1;
-  if (list2fpos(&argvars[0], &p1, &fnum, NULL, false) != OK
-      || (fnum >= 0 && fnum != curbuf->b_fnum)) {
-    return;
-  }
-
-  pos_T p2;
-  if (list2fpos(&argvars[1], &p2, &fnum, NULL, false) != OK
-      || (fnum >= 0 && fnum != curbuf->b_fnum)) {
+  int fnum1 = -1;
+  int fnum2 = -1;
+  pos_T p1, p2;
+  if (list2fpos(&argvars[0], &p1, &fnum1, NULL, false) != OK
+      || list2fpos(&argvars[1], &p2, &fnum2, NULL, false) != OK
+      || fnum1 != fnum2) {
     return;
   }
 
@@ -2866,6 +2862,18 @@ static void f_getregion(typval_T *argvars, typval_T *rettv, EvalFuncData fptr)
     return;
   }
 
+  buf_T *save_curbuf = curbuf;
+
+  if (fnum1 != 0) {
+    buf_T *findbuf = buflist_findnr(fnum1);
+    // buffer not loaded
+    if (findbuf == NULL || findbuf->b_ml.ml_mfp == NULL) {
+      return;
+    }
+    save_curbuf = curbuf;
+    curbuf = findbuf;
+  }
+
   const TriState save_virtual = virtual_op;
   virtual_op = virtual_active();
 
@@ -2948,6 +2956,10 @@ static void f_getregion(typval_T *argvars, typval_T *rettv, EvalFuncData fptr)
     tv_list_append_allocated_string(rettv->vval.v_list, akt);
   }
 
+  if (curbuf != save_curbuf) {
+    curbuf = save_curbuf;
+  }
+
   virtual_op = save_virtual;
 }