patch 8.2.3015: Vim9: Assigning to @# requires a string

Problem:    Vim9: Assigning to @# requires a string. (Naohiro Ono)
Solution:   Accent a number or a string. (closes #8396)

src/globals.h

@@ -418,6 +418,9 @@ EXTERN type_T t_blob INIT6(VAR_BLOB, 0, 0, TTFLAG_STATIC, NULL, NULL);
 EXTERN type_T t_job INIT6(VAR_JOB, 0, 0, TTFLAG_STATIC, NULL, NULL);
 EXTERN type_T t_channel INIT6(VAR_CHANNEL, 0, 0, TTFLAG_STATIC, NULL, NULL);
 
+// Special value used for @#.
+EXTERN type_T t_number_or_string INIT6(VAR_STRING, 0, 0, TTFLAG_STATIC, NULL, NULL);
+
 EXTERN type_T t_func_unknown INIT6(VAR_FUNC, -1, 0, TTFLAG_STATIC, &t_unknown, NULL);
 EXTERN type_T t_func_void INIT6(VAR_FUNC, -1, 0, TTFLAG_STATIC, &t_void, NULL);
 EXTERN type_T t_func_any INIT6(VAR_FUNC, -1, 0, TTFLAG_STATIC, &t_any, NULL);

src/testdir/test_vim9_assign.vim

@@ -1820,6 +1820,19 @@ def Test_assign_command_modifier()
   CheckDefAndScriptSuccess(lines)
 enddef
 
+def Test_assign_alt_buf_register()
+  var lines =<< trim END
+      edit 'file_b1'
+      var b1 = bufnr()
+      edit 'file_b2'
+      var b2 = bufnr()
+      assert_equal(b1, bufnr('#'))
+      @# = b2
+      assert_equal(b2, bufnr('#'))
+  END
+  CheckDefAndScriptSuccess(lines)
+enddef
+
 def Test_script_funcref_case()
   var lines =<< trim END
       var Len = (s: string): number => len(s) + 1

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3015,
 /**/
     3014,
 /**/

src/vim9compile.c

@@ -5852,7 +5852,7 @@ get_var_dest(
 	    return FAIL;
 	}
 	*dest = dest_reg;
-	*type = &t_string;
+	*type = name[1] == '#' ? &t_number_or_string : &t_string;
     }
     else if (STRNCMP(name, "g:", 2) == 0)
     {
@@ -5927,7 +5927,8 @@ generate_store_var(
 	case dest_env:
 	    return generate_STORE(cctx, ISN_STOREENV, 0, name + 1);
 	case dest_reg:
-	    return generate_STORE(cctx, ISN_STOREREG, name[1], NULL);
+	    return generate_STORE(cctx, ISN_STOREREG,
+					 name[1] == '@' ? '"' : name[1], NULL);
 	case dest_vimvar:
 	    return generate_STORE(cctx, ISN_STOREV, vimvaridx, NULL);
 	case dest_script:
@@ -6843,10 +6844,20 @@ compile_assignment(char_u *arg, exarg_T *eap, cmdidx_T cmdidx, cctx_T *cctx)
 			    goto theend;
 		    }
 		}
-		else if (*p != '=' && need_type(rhs_type, lhs.lhs_member_type,
+		else
+		{
+		    type_T *lhs_type = lhs.lhs_member_type;
+
+		    // Special case: assigning to @# can use a number or a
+		    // string.
+		    if (lhs_type == &t_number_or_string
+					    && rhs_type->tt_type == VAR_NUMBER)
+			lhs_type = &t_number;
+		    if (*p != '=' && need_type(rhs_type, lhs_type,
 					    -1, 0, cctx, FALSE, FALSE) == FAIL)
 		    goto theend;
 		}
+	    }
 	    else if (cmdidx == CMD_final)
 	    {
 		emsg(_(e_final_requires_a_value));

src/vim9execute.c

@@ -2182,8 +2182,7 @@ exec_instructions(ectx_T *ectx)
 
 		    --ectx->ec_stack.ga_len;
 		    tv = STACK_TV_BOT(0);
-		    write_reg_contents(reg == '@' ? '"' : reg,
+		    write_reg_contents(reg, tv_get_string(tv), -1, FALSE);
-						 tv_get_string(tv), -1, FALSE);
 		    clear_tv(tv);
 		}
 		break;