patch 8.2.1066: Lua arrays are zero based

Problem:    Lua arrays are zero based.
Solution:   Make Lua arrays one based. (Prabir Shrestha, closes #6347)
            Note: this is not backwards compatible.

runtime/doc/if_lua.txt

@@ -217,11 +217,15 @@ Vim's syntax for lists. Since lists are objects, changes in list references in
 Lua are reflected in Vim and vice-versa. A list "l" has the following
 properties and methods:
 
+NOTE: In patch 8.2.1066 array indexes were changed from zero-based to
+one-based.  You can check with: >
+	    if has("patch-8.2.1066")
+
 Properties
 ----------
 	o "#l" is the number of items in list "l", equivalent to "len(l)"
 	    in Vim.
-	o "l[k]" returns the k-th item in "l"; "l" is zero-indexed, as in Vim.
+	o "l[k]" returns the k-th item in "l"; "l" is one-indexed, as in Lua.
 	    To modify the k-th item, simply do "l[k] = newitem"; in
 	    particular, "l[k] = nil" removes the k-th item from "l".
 	o "l()" returns an iterator for "l".
@@ -237,11 +241,11 @@ Examples:
 	:let l = [1, 'item']
 	:lua l = vim.eval('l') -- same 'l'
 	:lua l:add(vim.list())
-	:lua l[0] = math.pi
+	:lua l[1] = math.pi
 	:echo l[0] " 3.141593
-	:lua l[0] = nil -- remove first item
+	:lua l[1] = nil -- remove first item
 	:lua l:insert(true, 1)
-	:lua print(l, #l, l[0], l[1], l[-1])
+	:lua print(l, #l, l[1], l[2])
 	:lua for item in l() do print(item) end
 <
 

src/if_lua.c

@@ -871,7 +871,13 @@ luaV_list_index(lua_State *L)
     list_T *l = luaV_unbox(L, luaV_List, 1);
     if (lua_isnumber(L, 2)) // list item?
     {
-	listitem_T *li = list_find(l, (long) luaL_checkinteger(L, 2));
+	long n = (long) luaL_checkinteger(L, 2);
+	listitem_T *li;
+
+	// Lua array index starts with 1 while Vim uses 0, subtract 1 to
+	// normalize.
+	n -= 1;
+	li = list_find(l, n);
 	if (li == NULL)
 	    lua_pushnil(L);
 	else
@@ -900,6 +906,10 @@ luaV_list_newindex(lua_State *L)
     list_T *l = luaV_unbox(L, luaV_List, 1);
     long n = (long) luaL_checkinteger(L, 2);
     listitem_T *li;
+
+    // Lua array index starts with 1 while Vim uses 0, subtract 1 to normalize.
+    n -= 1;
+
     if (l->lv_lock)
 	luaL_error(L, "list is locked");
     li = list_find(l, n);

src/testdir/test_lua.vim

@@ -327,8 +327,8 @@ func Test_lua_list()
   call assert_equal(7, luaeval('#l'))
   call assert_match('^list: \%(0x\)\?\x\+$', luaeval('tostring(l)'))
 
-  lua l[0] = 124
-  lua l[5] = nil
+  lua l[1] = 124
+  lua l[6] = nil
   lua l:insert('first')
   lua l:insert('xx', 3)
   call assert_equal(['first', 124, 'abc', 'xx', v:true, v:false, v:null, {'a': 1, 'b': 2, 'c': 3}], l)
@@ -367,22 +367,22 @@ func Test_lua_recursive_list()
   lua l = vim.list():add(1):add(2)
   lua l = l:add(l)
 
-  call assert_equal(1, luaeval('l[0]'))
-  call assert_equal(2, luaeval('l[1]'))
+  call assert_equal(1, luaeval('l[1]'))
+  call assert_equal(2, luaeval('l[2]'))
 
-  call assert_equal(1, luaeval('l[2][0]'))
-  call assert_equal(2, luaeval('l[2][1]'))
+  call assert_equal(1, luaeval('l[3][1]'))
+  call assert_equal(2, luaeval('l[3][2]'))
 
-  call assert_equal(1, luaeval('l[2][2][0]'))
-  call assert_equal(2, luaeval('l[2][2][1]'))
+  call assert_equal(1, luaeval('l[3][3][1]'))
+  call assert_equal(2, luaeval('l[3][3][2]'))
 
   call assert_equal('[1, 2, [...]]', string(luaeval('l')))
 
   call assert_match('^list: \%(0x\)\?\x\+$', luaeval('tostring(l)'))
-  call assert_equal(luaeval('tostring(l)'), luaeval('tostring(l[2])'))
+  call assert_equal(luaeval('tostring(l)'), luaeval('tostring(l[3])'))
 
-  call assert_equal(luaeval('l'), luaeval('l[2]'))
-  call assert_equal(luaeval('l'), luaeval('l[2][2]'))
+  call assert_equal(luaeval('l'), luaeval('l[3]'))
+  call assert_equal(luaeval('l'), luaeval('l[3][3]'))
 
   lua l = nil
 endfunc

src/version.c

@@ -754,6 +754,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1066,
 /**/
     1065,
 /**/