parser: proper unexpected eof errors in const declarations (#9712)

vlib/v/parser/parser.v

@@ -2719,7 +2719,6 @@ fn (mut p Parser) const_decl() ast.ConstDecl {
 	if is_pub {
 		p.next()
 	}
-	end_pos := p.tok.position()
 	const_pos := p.tok.position()
 	p.check(.key_const)
 	is_block := p.tok.kind == .lpar
@@ -2729,11 +2728,11 @@ fn (mut p Parser) const_decl() ast.ConstDecl {
 	mut fields := []ast.ConstField{}
 	mut comments := []ast.Comment{}
 	for {
-		if p.tok.kind == .eof {
-			p.error_with_pos('const declaration is missing closing `)`', const_pos)
+		comments = p.eat_comments({})
+		if is_block && p.tok.kind == .eof {
+			p.error('unexpected eof, expecting ´)´')
 			return ast.ConstDecl{}
 		}
-		comments = p.eat_comments({})
 		if p.tok.kind == .rpar {
 			break
 		}
@@ -2749,6 +2748,10 @@ fn (mut p Parser) const_decl() ast.ConstDecl {
 			p.error('const initializer fn literal is not a constant')
 			return ast.ConstDecl{}
 		}
+		if p.tok.kind == .eof {
+			p.error('unexpected eof, expecting an expression')
+			return ast.ConstDecl{}
+		}
 		expr := p.expr(0)
 		field := ast.ConstField{
 			name: full_name
@@ -2770,7 +2773,7 @@ fn (mut p Parser) const_decl() ast.ConstDecl {
 		p.check(.rpar)
 	}
 	return ast.ConstDecl{
-		pos: start_pos.extend_with_last_line(end_pos, p.prev_tok.line_nr)
+		pos: start_pos.extend_with_last_line(const_pos, p.prev_tok.line_nr)
 		fields: fields
 		is_pub: is_pub
 		end_comments: comments

vlib/v/parser/tests/const_missing_rpar_a.out

@@ -0,0 +1,3 @@
+vlib/v/parser/tests/const_missing_rpar_a.vv:3:1: error: unexpected eof, expecting ´)´
+    1 | const (
+    2 |     a = 5

vlib/v/parser/tests/const_missing_rpar_a.vv

@@ -0,0 +1,2 @@
+const (
+	a = 5

vlib/v/parser/tests/const_missing_rpar_b.out

@@ -0,0 +1,3 @@
+vlib/v/parser/tests/const_missing_rpar_b.vv:4:1: error: unexpected eof, expecting ´)´
+    2 |     a = 5
+    3 |     // foo

vlib/v/parser/tests/const_missing_rpar_b.vv

@@ -0,0 +1,3 @@
+const (
+	a = 5
+	// foo

vlib/v/parser/tests/const_only_keyword.out

@@ -0,0 +1,2 @@
+vlib/v/parser/tests/const_only_keyword.vv:2:1: error: unexpected eof, expecting name
+    1 | const

vlib/v/parser/tests/const_only_keyword.vv

@@ -0,0 +1 @@
+const

vlib/v/parser/tests/const_unexpected_eof.out

@@ -0,0 +1,2 @@
+vlib/v/parser/tests/const_unexpected_eof.vv:2:1: error: unexpected eof, expecting an expression
+    1 | const a =

vlib/v/parser/tests/const_unexpected_eof.vv

@@ -0,0 +1 @@
+const a =