v.parser: prohibit redeclaration of builtin types (#10563)

vlib/eventbus/README.md

@@ -85,18 +85,22 @@ fn on_error(receiver voidptr, e &Error, work &Work) {
 ```v oksyntax
 module main
 
+import eventbus
+
+const eb = eventbus.new()
+
 struct Work {
 	hours int
 }
 
-struct Error {
+struct AnError {
 	message string
 }
 
 fn do_work() {
 	work := Work{20}
 	// get a mutable Params instance & put some data into it
-	error := &Error{'Error: no internet connection.'}
+	error := &AnError{'Error: no internet connection.'}
 	// publish the event
 	eb.publish('error', work, error)
 }

vlib/v/ast/table.v

@@ -542,11 +542,7 @@ pub fn (t &Table) unalias_num_type(typ Type) Type {
 	return typ
 }
 
-[inline]
-pub fn (mut t Table) register_type_symbol(typ TypeSymbol) int {
-	// println('register_type_symbol( $typ.name )')
-	existing_idx := t.type_idxs[typ.name]
-	if existing_idx > 0 {
+fn (mut t Table) check_for_already_registered_symbol(typ TypeSymbol, existing_idx int) int {
 	ex_type := t.type_symbols[existing_idx]
 	match ex_type.kind {
 		.placeholder {
@@ -578,8 +574,29 @@ pub fn (mut t Table) register_type_symbol(typ TypeSymbol) int {
 			return -1
 		}
 	}
+	return -2
+}
+
+[inline]
+pub fn (mut t Table) register_type_symbol(typ TypeSymbol) int {
+	mut typ_idx := -2
+	mut existing_idx := t.type_idxs[typ.name]
+	if existing_idx > 0 {
+		typ_idx = t.check_for_already_registered_symbol(typ, existing_idx)
+		if typ_idx != -2 {
+			return typ_idx
 		}
-	typ_idx := t.type_symbols.len
+	}
+	if typ.mod == 'main' {
+		existing_idx = t.type_idxs[typ.name.trim_prefix('main.')]
+		if existing_idx > 0 {
+			typ_idx = t.check_for_already_registered_symbol(typ, existing_idx)
+			if typ_idx != -2 {
+				return typ_idx
+			}
+		}
+	}
+	typ_idx = t.type_symbols.len
 	t.type_symbols << typ
 	t.type_idxs[typ.name] = typ_idx
 	return typ_idx

vlib/v/parser/tests/prohibit_redeclaration_of_builtin_types.out

@@ -0,0 +1,3 @@
+vlib/v/parser/tests/prohibit_redeclaration_of_builtin_types.vv:1:8: error: cannot register struct `Option`, another type with this name exists
+    1 | struct Option {}
+      |        ~~~~~~

vlib/v/parser/tests/prohibit_redeclaration_of_builtin_types.vv

@@ -0,0 +1 @@
+struct Option {}