parser: allow `const x = 0` consts outside of const blocks

vlib/v/ast/ast.v

@@ -179,6 +179,7 @@ pub:
 pub mut:
 	fields       []ConstField // all the const fields in the `const (...)` block
 	end_comments []Comment // comments that after last const field
+	is_block     bool // const() block
 }
 
 pub struct StructDecl {

vlib/v/fmt/fmt.v

@@ -1992,7 +1992,10 @@ pub fn (mut f Fmt) const_decl(it ast.ConstDecl) {
 		f.writeln('const ()\n')
 		return
 	}
-	f.writeln('const (')
+	f.write('const ')
+	if it.is_block {
+		f.writeln(' (')
+	}
 	mut max := 0
 	for field in it.fields {
 		if field.name.len > max {
@@ -2017,7 +2020,11 @@ pub fn (mut f Fmt) const_decl(it ast.ConstDecl) {
 	}
 	f.comments_after_last_field(it.end_comments)
 	f.indent--
+	if it.is_block {
 		f.writeln(')\n')
+	} else {
+		f.writeln('')
+	}
 }
 
 fn (mut f Fmt) global_decl(it ast.GlobalDecl) {

vlib/v/parser/parser.v

@@ -1799,11 +1799,16 @@ fn (mut p Parser) const_decl() ast.ConstDecl {
 	end_pos := p.tok.position()
 	const_pos := p.tok.position()
 	p.check(.key_const)
+	is_block := p.tok.kind == .lpar
+	/*
 	if p.tok.kind != .lpar {
 		p.error_with_pos('const declaration is missing parentheses `( ... )`', const_pos)
 		return ast.ConstDecl{}
 	}
+	*/
+	if is_block {
 		p.next() // (
+	}
 	mut fields := []ast.ConstField{}
 	mut comments := []ast.Comment{}
 	for {
@@ -1840,14 +1845,20 @@ fn (mut p Parser) const_decl() ast.ConstDecl {
 		fields << field
 		p.global_scope.register(field)
 		comments = []
+		if !is_block {
+			break
+		}
 	}
 	p.top_level_statement_end()
+	if is_block {
 		p.check(.rpar)
+	}
 	return ast.ConstDecl{
 		pos: start_pos.extend_with_last_line(end_pos, p.prev_tok.line_nr)
 		fields: fields
 		is_pub: is_pub
 		end_comments: comments
+		is_block: is_block
 	}
 }
 

vlib/v/tests/const_test.v

@@ -6,6 +6,8 @@ pub const (
 	e = 9
 )
 
+pub const x = 10
+
 fn test_const() {
 	assert a == 1
 	assert d == 11
@@ -21,13 +23,12 @@ fn foo_decode(name string) ?Foo {
 	if name == 'baz' {
 		return error('baz is not allowed')
 	}
-
 	return Foo{name}
 }
 
 pub const  (
 	def = foo_decode('baz') or { Foo{} }
-	bar = foo_decode('bar')?
+	bar = foo_decode('bar') ?
 )
 
 fn test_opt_const() {