From 63bc769ce69a29caa6b9bf6300c7acea3ed78123 Mon Sep 17 00:00:00 2001
From: Felix Ehlers <fleximus@users.noreply.github.com>
Date: Wed, 7 Jan 2026 08:26:35 +0100
Subject: [PATCH] fmt: fix parser failing on duplicate methods in $if/$else
 blocks (fix #26271) (#26278)

---
 .../comptime_if_duplicate_method_keep.vv      | 35 +++++++++++++++++++
 vlib/v/parser/fn.v                            |  4 ++-
 2 files changed, 38 insertions(+), 1 deletion(-)
 create mode 100644 vlib/v/fmt/tests/comptime_if_duplicate_method_keep.vv

diff --git a/vlib/v/fmt/tests/comptime_if_duplicate_method_keep.vv b/vlib/v/fmt/tests/comptime_if_duplicate_method_keep.vv
new file mode 100644
index 000000000..32cd4ceb7
--- /dev/null
+++ b/vlib/v/fmt/tests/comptime_if_duplicate_method_keep.vv
@@ -0,0 +1,35 @@
+// Test for issue #26271: v fmt fails on mutually exclusive $if blocks with duplicate method definitions
+module main
+
+struct MyType {
+	value int
+}
+
+$if foo ? {
+	pub fn (x MyType) str() string {
+		return 'foo mode'
+	}
+} $else {
+	pub fn (x MyType) str() string {
+		return 'normal mode'
+	}
+}
+
+$if bar ? {
+	fn (m MyType) debug() string {
+		return 'bar debug'
+	}
+} $else $if baz ? {
+	fn (m MyType) debug() string {
+		return 'baz debug'
+	}
+} $else {
+	fn (m MyType) debug() string {
+		return 'default debug'
+	}
+}
+
+fn main() {
+	t := MyType{42}
+	println(t.str())
+}
diff --git a/vlib/v/parser/fn.v b/vlib/v/parser/fn.v
index 4bbb4225e..9216f6287 100644
--- a/vlib/v/parser/fn.v
+++ b/vlib/v/parser/fn.v
@@ -658,7 +658,9 @@ fn (mut p Parser) fn_decl() ast.FnDecl {
 					is_duplicate = !type_sym.info.has_method(name)
 				}
 			}
-			if is_duplicate {
+			// when formatting, methods in mutually exclusive $if/$else branches
+			// may appear as duplicates since all branches are parsed
+			if is_duplicate && !p.pref.is_fmt {
 				if type_sym.kind == .enum
 					&& name in ['is_empty', 'has', 'all', 'set', 'set_all', 'clear', 'clear_all', 'toggle', 'zero', 'from'] {
 					if enum_fn := type_sym.find_method(name) {
-- 
2.39.5