From 9e7bce4efea255c1ba7ed0c4c7884f0ee9a0bee6 Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Tue, 21 Apr 2026 05:24:00 +0300
Subject: [PATCH] vfmt: fix format error on types (fixes #25496)

---
 vlib/v/fmt/fmt.v                   | 24 +++++++++++++++++++++++-
 vlib/v/fmt/tests/types_expected.vv |  6 ++++++
 vlib/v/fmt/tests/types_input.vv    |  6 ++++++
 vlib/v/parser/parse_type.v         | 27 +++++++++++++++++++++++----
 4 files changed, 58 insertions(+), 5 deletions(-)

diff --git a/vlib/v/fmt/fmt.v b/vlib/v/fmt/fmt.v
index 38ae54431..172368637 100644
--- a/vlib/v/fmt/fmt.v
+++ b/vlib/v/fmt/fmt.v
@@ -1847,6 +1847,28 @@ struct Variant {
 	id   int
 }
 
+fn (mut f Fmt) sum_type_variant_comments(variant ast.TypeNode) {
+	if variant.end_comments.len == 0 {
+		return
+	}
+	mut same_line_comments := []ast.Comment{}
+	mut follow_up_comments := []ast.Comment{}
+	for comment in variant.end_comments {
+		if comment.pos.line_nr == variant.pos.last_line {
+			same_line_comments << comment
+		} else {
+			follow_up_comments << comment
+		}
+	}
+	if same_line_comments.len > 0 {
+		f.comments(same_line_comments, has_nl: false)
+	}
+	if follow_up_comments.len > 0 {
+		f.writeln('')
+		f.comments(follow_up_comments, has_nl: false, level: .indent)
+	}
+}
+
 pub fn (mut f Fmt) sum_type_decl(node ast.SumTypeDecl) {
 	f.attrs(node.attrs)
 	start_pos := f.out.len
@@ -1886,7 +1908,7 @@ pub fn (mut f Fmt) sum_type_decl(node ast.SumTypeDecl) {
 		}
 		f.write(variant.name)
 		if node.variants[variant.id].end_comments.len > 0 && is_multiline {
-			f.comments(node.variants[variant.id].end_comments, has_nl: false)
+			f.sum_type_variant_comments(node.variants[variant.id])
 		}
 	}
 	if !is_multiline {
diff --git a/vlib/v/fmt/tests/types_expected.vv b/vlib/v/fmt/tests/types_expected.vv
index e70f2ac52..b868ee776 100644
--- a/vlib/v/fmt/tests/types_expected.vv
+++ b/vlib/v/fmt/tests/types_expected.vv
@@ -11,6 +11,12 @@ pub type Callback = ConnectedCallback // connected callback
 	| DisconnectedCallback // disconnected callback
 	| LoggedOffCallback // logged off callback
 
+type SumResp = string
+	| int
+	// | f64
+	| map[string]int
+	| map[string]bool
+
 struct ConnectedCallback {}
 
 struct DisconnectedCallback {}
diff --git a/vlib/v/fmt/tests/types_input.vv b/vlib/v/fmt/tests/types_input.vv
index 97028fe5f..f73e6e5ac 100644
--- a/vlib/v/fmt/tests/types_input.vv
+++ b/vlib/v/fmt/tests/types_input.vv
@@ -11,6 +11,12 @@ pub type Callback = ConnectedCallback 	// connected callback
 	| DisconnectedCallback 	// disconnected callback
 	| LoggedOffCallback // logged off callback
 
+type SumResp = string
+	| int
+	// | f64
+	| map[string]int
+	| map[string]bool
+
 struct ConnectedCallback{}
 struct DisconnectedCallback{}
 struct LoggedOnCallback{}
diff --git a/vlib/v/parser/parse_type.v b/vlib/v/parser/parse_type.v
index 0206d9162..bbbe3d883 100644
--- a/vlib/v/parser/parse_type.v
+++ b/vlib/v/parser/parse_type.v
@@ -494,6 +494,23 @@ fn (mut p Parser) parse_inline_sum_type() ast.Type {
 
 // parse_sum_type_variants parses several types separated with a pipe and returns them as a list with at least one node.
 // If there is less than one node, it will add an error to the error list.
+fn (p &Parser) has_follow_up_sum_type_pipe() bool {
+	mut line := p.prev_tok.line_nr + p.prev_tok.lit.count('\n')
+	if p.tok.kind != .comment || p.tok.line_nr > line + 1 {
+		return false
+	}
+	mut tok := p.tok
+	mut next_tok := p.peek_tok
+	mut peek_idx := 2
+	for tok.kind == .comment && tok.line_nr <= line + 1 {
+		line = tok.line_nr + tok.lit.count('\n')
+		tok = next_tok
+		next_tok = p.peek_token(peek_idx)
+		peek_idx++
+	}
+	return tok.kind == .pipe && tok.line_nr <= line + 1
+}
+
 fn (mut p Parser) parse_sum_type_variants() []ast.TypeNode {
 	p.inside_sum_type = true
 	defer {
@@ -503,10 +520,12 @@ fn (mut p Parser) parse_sum_type_variants() []ast.TypeNode {
 	for {
 		type_start_pos := p.tok.pos()
 		typ := p.parse_type()
-		end_comments := p.eat_comments(same_line: true)
-		// TODO: needs to be its own var, otherwise TCC fails because of a known stack error
-		prev_tok := p.prev_tok
-		type_end_pos := prev_tok.pos()
+		// Keep the type node position on the variant itself; trailing comments are stored separately.
+		type_end_pos := p.prev_tok.pos()
+		mut end_comments := p.eat_comments(same_line: true)
+		if p.has_follow_up_sum_type_pipe() {
+			end_comments << p.eat_comments(follow_up: true)
+		}
 		type_pos := type_start_pos.extend(type_end_pos)
 		types << ast.TypeNode{
 			typ:          typ
-- 
2.39.5