Commit: patch 9.1.1942: Vim9: Assignment to read-only registers @: and @% is allowed

[Christian Brabandt]

patch 9.1.1942: Vim9: Assignment to read-only registers @: and @% is allowed

Commit: https://github.com/vim/vim/commit/e5c5378cd27a7a370af7868ec1e4d005b335b2f9
Author: Doug Kearns <dougk...@gmail.com>
Date: Sun Nov 30 15:26:22 2025 +0000

patch 9.1.1942: Vim9: Assignment to read-only registers @: and @% is allowed

Problem: Assignment to read-only registers @: and @% is allowed during
compilation.
Solution: Abort compilation and emit an E354 error when assigning to
these registers (Doug Kearns).

Fix the E354 error emitted when attempting to declare @: with :var so
that it references the correct register, @:, rather than the garbage
string "^@".

closes: #18806

Signed-off-by: Doug Kearns <dougk...@gmail.com>
Signed-off-by: Yegappan Lakshmanan <yega...@yahoo.com>
Signed-off-by: Christian Brabandt <c...@256bit.org>

diff --git a/src/testdir/test_vim9_assign.vim b/src/testdir/test_vim9_assign.vim
index b7b09c972..a8c6c01cb 100644
--- a/src/testdir/test_vim9_assign.vim
+++ b/src/testdir/test_vim9_assign.vim
@@ -1592,12 +1592,17 @@ def Test_assignment_failure()
v9.CheckDefFailure(['var $VAR = 5'], 'E1016: Cannot declare an environment variable:')
v9.CheckScriptFailure(['vim9script', 'var $ENV = "xxx"'], 'E1016:')

+ # read-only registers
+ v9.CheckDefAndScriptFailure(['var @. = 5'], ['E354:', 'E1066:'], 1)
+ v9.CheckDefAndScriptFailure(['var @. = 5'], ['E354:', 'E1066:'], 1)
+ v9.CheckDefAndScriptFailure(['var @% = 5'], ['E354:', 'E1066:'], 1)
+ v9.CheckDefAndScriptFailure(['var @: = 5'], ['E354:', 'E1066:'], 1)
if has('dnd')
- v9.CheckDefFailure(['var @~ = 5'], 'E1066:')
+ v9.CheckDefAndScriptFailure(['var @~ = 5'], ['E354:', 'E1066:'], 1)
else
- v9.CheckDefFailure(['var @~ = 5'], 'E354:')
- v9.CheckDefFailure(['@~ = 5'], 'E354:')
+ v9.CheckDefAndScriptFailure(['var @~ = 5'], ['E354:', 'E1066:'], 1)
endif
+
v9.CheckDefFailure(['var @a = 5'], 'E1066:')
v9.CheckDefFailure(['var @/ = "x"'], 'E1066:')
v9.CheckScriptFailure(['vim9script', 'var @a = "abc"'], 'E1066:')
diff --git a/src/testdir/test_vim9_expr.vim b/src/testdir/test_vim9_expr.vim
index bbc9e1065..8e5a53d51 100644
--- a/src/testdir/test_vim9_expr.vim
+++ b/src/testdir/test_vim9_expr.vim
@@ -3352,7 +3352,11 @@ def Test_expr9_register()
END
v9.CheckDefAndScriptSuccess(lines)

+ # read-only registers
v9.CheckDefAndScriptFailure(["@. = 'yes'"], 'E354:', 1)
+ v9.CheckDefAndScriptFailure(["@% = 'yes'"], 'E354:', 1)
+ v9.CheckDefAndScriptFailure(["@: = 'yes'"], 'E354:', 1)
+ v9.CheckDefAndScriptFailure(["@~ = 'yes'"], 'E354:', 1)
enddef

" This is slow when run under valgrind.
diff --git a/src/version.c b/src/version.c
index a8bff776a..81e8cf3b7 100644
--- a/src/version.c
+++ b/src/version.c
@@ -729,6 +729,8 @@ static char *(features[]) =

static int included_patches[] =
{ /* Add new patch number below this line */
+/**/
+ 1942,
/**/
1941,
/**/
diff --git a/src/vim9compile.c b/src/vim9compile.c
index cab48bb8a..43f8dcb7f 100644
--- a/src/vim9compile.c
+++ b/src/vim9compile.c
@@ -1464,7 +1464,9 @@ vim9_declare_error(char_u *name)
static int
valid_dest_reg(int name)
{
- if ((name == '@' || valid_yank_reg(name, FALSE)) && name != '.')
+ if (name == '@')
+ name = '"';
+ if (name == '/' || name == '=' || valid_yank_reg(name, TRUE))
return TRUE;
emsg_invreg(name);
return FAIL;