patch 8.1.1188: not all Vim variables require the v: prefix

Problem:    Not all Vim variables require the v: prefix.
Solution:   When scriptversion is 3 all Vim variables can only be used with
            the v: prefix.  (Ken Takata, closes #4274)

runtime/doc/eval.txt

@@ -1688,7 +1688,8 @@ v:count		The count given for the last Normal mode command.  Can be used
 		When there are two counts, as in "3d2w", they are multiplied,
 		just like what happens in the command, "d6w" for the example.
 		Also used for evaluating the 'formatexpr' option.
-		"count" also works, for backwards compatibility.
+		"count" also works, for backwards compatibility, unless
+		|scriptversion| is 3 or higher.
 
 					*v:count1* *count1-variable*
 v:count1	Just like "v:count", but defaults to one when no count is
@@ -1720,7 +1721,8 @@ v:errmsg	Last given error message.  It's allowed to set this variable.
 	:silent! next
 	:if v:errmsg != ""
 	:  ... handle error
-<		"errmsg" also works, for backwards compatibility.
+<		"errmsg" also works, for backwards compatibility, unless
+		|scriptversion| is 3 or higher.
 
 				*v:errors* *errors-variable* *assert-return*
 v:errors	Errors found by assert functions, such as |assert_true()|.
@@ -2023,7 +2025,8 @@ v:shell_error	Result of the last shell command.  When non-zero, the last
 	:if v:shell_error
 	:  echo 'could not rename "foo" to "bar"!'
 	:endif
-<		"shell_error" also works, for backwards compatibility.
+<		"shell_error" also works, for backwards compatibility, unless
+		|scriptversion| is 3 or higher.
 
 					*v:statusmsg* *statusmsg-variable*
 v:statusmsg	Last given status message.  It's allowed to set this variable.
@@ -2123,7 +2126,8 @@ v:testing	Must be set before using `test_garbagecollect_now()`.
 v:this_session	Full filename of the last loaded or saved session file.  See
 		|:mksession|.  It is allowed to set this variable.  When no
 		session file has been saved, this variable is empty.
-		"this_session" also works, for backwards compatibility.
+		"this_session" also works, for backwards compatibility, unless
+		|scriptversion| is 3 or higher
 
 					*v:throwpoint* *throwpoint-variable*
 v:throwpoint	The point where the exception most recently caught and not
@@ -2154,7 +2158,7 @@ v:val		Value of the current item of a |List| or |Dictionary|.  Only
 v:version	Version number of Vim: Major version number times 100 plus
 		minor version number.  Version 5.0 is 500.  Version 5.1 (5.01)
 		is 501.  Read-only.  "version" also works, for backwards
-		compatibility.
+		compatibility, unless |scriptversion| is 3 or higher.
 		Use |has()| to check if a certain patch was included, e.g.: >
 			if has("patch-7.4.123")
 <		Note that patch numbers are specific to the version, thus both

src/eval.c

@@ -7672,10 +7672,14 @@ find_var_ht(char_u *name, char_u **varname)
 	    return NULL;
 	*varname = name;
 
-	/* "version" is "v:version" in all scopes */
+	// "version" is "v:version" in all scopes if scriptversion < 3.
+	// Same for a few other variables marked with VV_COMPAT.
+	if (current_sctx.sc_version < 3)
+	{
 	    hi = hash_find(&compat_hashtab, name);
 	    if (!HASHITEM_EMPTY(hi))
 		return &compat_hashtab;
+	}
 
 	ht = get_funccal_local_ht();
 	if (ht == NULL)

src/ex_cmds2.c

@@ -5127,7 +5127,7 @@ ex_scriptversion(exarg_T *eap UNUSED)
     nr = getdigits(&eap->arg);
     if (nr == 0 || *eap->arg != NUL)
 	emsg(_(e_invarg));
-    else if (nr > 2)
+    else if (nr > 3)
 	semsg(_("E999: scriptversion not supported: %d"), nr);
     else
 	current_sctx.sc_version = nr;

src/testdir/test_eval_stuff.vim

@@ -154,6 +154,22 @@ func Test_string_concat_scriptversion1()
   endif
 endfunc
 
+scriptversion 3
+func Test_vvar_scriptversion3()
+  call assert_fails('echo version', 'E121:')
+  call assert_false(exists('version'))
+  let version = 1
+  call assert_equal(1, version)
+endfunc
+
+scriptversion 2
+func Test_vvar_scriptversion2()
+  call assert_true(exists('version'))
+  echo version
+  call assert_fails('let version = 1', 'E46:')
+  call assert_equal(v:version, version)
+endfunc
+
 func Test_scriptversion()
   call writefile(['scriptversion 9'], 'Xversionscript')
   call assert_fails('source Xversionscript', 'E999:')

src/version.c

@@ -771,6 +771,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1188,
 /**/
     1187,
 /**/