parser: protect against infinite loops in -silent mode over invalid .v files

vlib/v/parser/fn.v

@@ -258,6 +258,7 @@ fn (mut p Parser) fn_decl() ast.FnDecl {
 		for param in params {
 			if p.scope.known_var(param.name) {
 				p.error_with_pos('redefinition of parameter `$param.name`', param.pos)
+				break
 			}
 			p.scope.register(param.name, ast.Var{
 				name: param.name
@@ -456,6 +457,7 @@ fn (mut p Parser) fn_args() ([]table.Param, bool, bool) {
 					}
 				} else if is_shared || is_atomic {
 					p.error_with_pos('generic object cannot be `atomic`or `shared`', pos)
+					break
 				}
 				// if arg_type.is_ptr() {
 				// p.error('cannot mut')
@@ -476,6 +478,7 @@ fn (mut p Parser) fn_args() ([]table.Param, bool, bool) {
 				if is_variadic {
 					p.error_with_pos('cannot use ...(variadic) with non-final parameter no $arg_no',
 						pos)
+					break
 				}
 				p.next()
 			}
@@ -488,6 +491,10 @@ fn (mut p Parser) fn_args() ([]table.Param, bool, bool) {
 				type_source_name: sym.source_name
 			}
 			arg_no++
+			if arg_no > 1024 {
+				p.error_with_pos('too many args', pos)
+				break
+			}
 		}
 	} else {
 		for p.tok.kind != .rpar {
@@ -532,6 +539,7 @@ fn (mut p Parser) fn_args() ([]table.Param, bool, bool) {
 				} else if is_shared || is_atomic {
 					p.error_with_pos('generic object cannot be `atomic` or `shared`',
 						pos)
+					break
 				}
 				typ = typ.set_nr_muls(1)
 				if is_shared {
@@ -557,6 +565,7 @@ fn (mut p Parser) fn_args() ([]table.Param, bool, bool) {
 				if is_variadic && p.tok.kind == .comma {
 					p.error_with_pos('cannot use ...(variadic) with non-final parameter $arg_name',
 						arg_pos[i])
+					break
 				}
 			}
 			if p.tok.kind != .rpar {

vlib/v/parser/parser.v

@@ -813,6 +813,13 @@ pub fn (mut p Parser) error_with_pos(s string, pos token.Position) {
 			message: s
 		}
 	}
+	if p.pref.output_mode == .silent {
+		// Normally, parser errors mean that the parser exits immediately, so there can be only 1 parser error.
+		// In the silent mode however, the parser continues to run, even though it would have stopped. Some
+		// of the parser logic does not expect that, and may loop forever.
+		// The p.next() here is needed, so the parser is more robust, and *always* advances, even in the -silent mode.
+		p.next()
+	}
 }
 
 pub fn (mut p Parser) warn_with_pos(s string, pos token.Position) {