patch 8.2.2565: Vim9: "..=" not always recognized

Problem:    Vim9: "..=" not always recognized.
Solution:   Do not consider "..=" to be string concatenation. (closes #7905)

src/eval.c

@@ -2849,11 +2849,12 @@ eval5(char_u **arg, typval_T *rettv, evalarg_T *evalarg)
 	int	    vim9script = in_vim9script();
 
 	// "." is only string concatenation when scriptversion is 1
-	// "+=" and "-=" are assignment
+	// "+=", "-=" and "..=" are assignments
 	p = eval_next_non_blank(*arg, evalarg, &getnext);
 	op = *p;
 	concat = op == '.' && (*(p + 1) == '.' || current_sctx.sc_version < 2);
-	if ((op != '+' && op != '-' && !concat) || p[1] == '=')
+	if ((op != '+' && op != '-' && !concat) || p[1] == '='
+					       || (p[1] == '.' && p[2] == '='))
 	    break;
 
 	evaluate = evalarg == NULL ? 0 : (evalarg->eval_flags & EVAL_EVALUATE);
@@ -3080,9 +3081,10 @@ eval6(
 #endif
 	int	    error;
 
+	// "*=", "/=" and "%=" are assignments
 	p = eval_next_non_blank(*arg, evalarg, &getnext);
 	op = *p;
-	if (op != '*' && op != '/' && op != '%')
+	if ((op != '*' && op != '/' && op != '%') || p[1] == '=')
 	    break;
 
 	evaluate = evalarg == NULL ? 0 : (evalarg->eval_flags & EVAL_EVALUATE);

src/testdir/test_vim9_assign.vim

@@ -1099,6 +1099,44 @@ def Test_assign_dict_unknown_type()
   CheckScriptSuccess(lines)
 enddef
 
+def Test_assign_dict_with_op()
+  var lines =<< trim END
+    vim9script
+    var ds: dict<string> = {a: 'x'}
+    ds['a'] ..= 'y'
+    ds.a ..= 'z'
+    assert_equal('xyz', ds.a)
+
+    var dn: dict<number> = {a: 9}
+    dn['a'] += 2
+    assert_equal(11, dn.a)
+    dn.a += 2
+    assert_equal(13, dn.a)
+
+    dn['a'] -= 3
+    assert_equal(10, dn.a)
+    dn.a -= 2
+    assert_equal(8, dn.a)
+
+    dn['a'] *= 2
+    assert_equal(16, dn.a)
+    dn.a *= 2
+    assert_equal(32, dn.a)
+
+    dn['a'] /= 3
+    assert_equal(10, dn.a)
+    dn.a /= 2
+    assert_equal(5, dn.a)
+
+    dn['a'] %= 3
+    assert_equal(2, dn.a)
+    dn.a %= 6
+    assert_equal(2, dn.a)
+  END
+  # TODO: this should also work with a :def function
+  CheckScriptSuccess(lines)
+enddef
+
 def Test_assign_lambda()
   # check if assign a lambda to a variable which type is func or any.
   var lines =<< trim END

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2565,
 /**/
     2564,
 /**/