parser: disallow module name as expression name

vlib/v/parser/assign.v

@@ -202,6 +202,10 @@ fn (mut p Parser) partial_assign_stmt(left []ast.Expr, left_comments []ast.Comme
 		match mut lx {
 			ast.Ident {
 				if op == .decl_assign {
+					if p.mod == lx.name {
+						return p.error_with_pos('expression names cannot match module name',
+							lx.pos)
+					}
 					if p.scope.known_var(lx.name) {
 						return p.error_with_pos('redefinition of `${lx.name}`', lx.pos)
 					}

vlib/v/parser/fn.v

@@ -373,6 +373,12 @@ fn (mut p Parser) fn_decl() ast.FnDecl {
 	params << args2
 	if !are_args_type_only {
 		for k, param in params {
+			if p.mod == param.name {
+				p.error_with_pos('parameter names cannot match module name', param.pos)
+				return ast.FnDecl{
+					scope: 0
+				}
+			}
 			if p.scope.known_var(param.name) {
 				p.error_with_pos('redefinition of parameter `${param.name}`', param.pos)
 				return ast.FnDecl{

vlib/v/parser/parser.v

@@ -3677,6 +3677,9 @@ fn (mut p Parser) const_decl() ast.ConstDecl {
 		if p.tok.kind == .decl_assign {
 			p.error_with_pos('cannot use `:=` to declare a const, use `=` instead', p.tok.pos())
 		}
+		if p.mod == name {
+			p.error_with_pos('const names cannot match module name', pos)
+		}
 		p.check(.assign)
 		end_comments << p.eat_comments()
 		if p.tok.kind == .key_fn {