checker: add more checks for multivar assignments

Makefile

@@ -94,10 +94,10 @@ $(TMPVC)/.git/config:
 	$(MAKE) fresh_vc
 
 selfcompile:
-	./v -csource keep -cg -o v cmd/v
+	./v -keepc -cg -o v cmd/v
 
 selfcompile-static:
-	./v -csource keep -cg -cflags '--static' -o v-static cmd/v
+	./v -keepc -cg -cflags '--static' -o v-static cmd/v
 
 modules: module_builtin module_strings module_strconv
 module_builtin:

vlib/v/checker/checker.v

@@ -590,14 +590,21 @@ pub fn (c mut Checker) assign_stmt(assign_stmt mut ast.AssignStmt) {
 		}
 		right_type := c.expr(assign_stmt.right[0])
 		right_type_sym := c.table.get_type_symbol(right_type)
-		mr_info := right_type_sym.mr_info()
 		if right_type_sym.kind != .multi_return {
-			c.error('wrong number of vars', assign_stmt.pos)
+			c.error('expression on the right does not return multiple values, while at least $assign_stmt.left.len are expected', assign_stmt.pos)
+			return
+		}
+		mr_info := right_type_sym.mr_info()
+		if mr_info.types.len < assign_stmt.left.len {
+			c.error('right expression returns only $mr_info.types.len values, but left one expects $assign_stmt.left.len', assign_stmt.pos)
 		}
 		mut scope := c.file.scope.innermost(assign_stmt.pos.pos)
 		for i, _ in assign_stmt.left {
 			mut ident := assign_stmt.left[i]
 			mut ident_var_info := ident.var_info()
+			if i >= mr_info.types.len {
+				continue
+			}
 			val_type := mr_info.types[i]
 			if assign_stmt.op == .assign {
 				var_type := c.expr(ident)

vlib/v/parser/parser.v

@@ -1712,9 +1712,9 @@ fn (p mut Parser) assign_stmt() ast.Stmt {
 		p.next()
 	}
 	idents := p.parse_assign_lhs()
-	pos := p.tok.position()
 	op := p.tok.kind
 	p.next()	// :=, =
+	pos := p.tok.position()
 	exprs := p.parse_assign_rhs()
 	is_decl := op == .decl_assign
 	for i, ident in idents {