parser: check the redefinition of built-in IError (#13606)

vlib/v/parser/struct.v

@@ -47,6 +47,10 @@ fn (mut p Parser) struct_decl() ast.StructDecl {
 			name_pos)
 		return ast.StructDecl{}
 	}
+	if name == 'IError' && p.mod != 'builtin' {
+		p.error_with_pos('cannot register struct `IError`, it is builtin interface type',
+			name_pos)
+	}
 	generic_types, _ := p.parse_generic_types()
 	no_body := p.tok.kind != .lcbr
 	if language == .v && no_body {
@@ -453,6 +457,10 @@ fn (mut p Parser) interface_decl() ast.InterfaceDecl {
 	name_pos := p.tok.pos()
 	p.check_for_impure_v(language, name_pos)
 	modless_name := p.check_name()
+	if modless_name == 'IError' && p.mod != 'builtin' {
+		p.error_with_pos('cannot register interface `IError`, it is builtin interface type',
+			name_pos)
+	}
 	mut interface_name := ''
 	if language == .js {
 		interface_name = 'JS.' + modless_name

vlib/v/parser/tests/register_ierror_interface.out

@@ -0,0 +1,5 @@
+vlib/v/parser/tests/register_ierror_interface.vv:1:11: error: cannot register interface `IError`, it is builtin interface type
+    1 | interface IError {
+      |           ~~~~~~
+    2 |     foo() string
+    3 | }

vlib/v/parser/tests/register_ierror_interface.vv

@@ -0,0 +1,7 @@
+interface IError {
+	foo() string
+}
+
+fn main() {
+	println('Hello World')
+}

vlib/v/parser/tests/register_ierror_struct.out

@@ -0,0 +1,5 @@
+vlib/v/parser/tests/register_ierror_struct.vv:1:8: error: cannot register struct `IError`, it is builtin interface type
+    1 | struct IError {
+      |        ~~~~~~
+    2 |     msg string
+    3 | }

vlib/v/parser/tests/register_ierror_struct.vv

@@ -0,0 +1,7 @@
+struct IError {
+	msg string
+}
+
+fn main() {
+	println('Hello World')
+}