From 006d3ab74aededae71901a467a4f5e00c82296b7 Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Wed, 25 Mar 2026 16:42:24 +0300
Subject: [PATCH] parser: fix initializing anonymous struct (fixes #16207)

---
 vlib/v/checker/struct.v                       | 15 +++++++++++++
 vlib/v/parser/expr.v                          | 22 ++++++++++++++++++-
 .../structs/anon_struct_local_init_test.v     | 12 ++++++++++
 3 files changed, 48 insertions(+), 1 deletion(-)
 create mode 100644 vlib/v/tests/structs/anon_struct_local_init_test.v

diff --git a/vlib/v/checker/struct.v b/vlib/v/checker/struct.v
index 7c8133efd..c48dff31b 100644
--- a/vlib/v/checker/struct.v
+++ b/vlib/v/checker/struct.v
@@ -694,6 +694,21 @@ fn (mut c Checker) struct_init(mut node ast.StructInit, is_field_zero_struct_ini
 			return ast.void_type
 		}
 	}
+	if c.anon_struct_should_be_mut {
+		mut anon_type_sym := c.table.sym(node.typ)
+		if anon_type_sym.info is ast.Struct && anon_type_sym.info.is_anon {
+			mut anon_info := anon_type_sym.info as ast.Struct
+			mut anon_fields := []ast.StructField{cap: anon_info.fields.len}
+			for field in anon_info.fields {
+				anon_fields << ast.StructField{
+					...field
+					is_mut: true
+				}
+			}
+			anon_info.fields = anon_fields
+			anon_type_sym.info = anon_info
+		}
+	}
 	// Make sure the first letter is capital, do not allow e.g. `x := string{}`,
 	// but `x := T{}` is ok.
 	if !c.is_builtin_mod && !c.inside_unsafe && type_sym.language == .v
diff --git a/vlib/v/parser/expr.v b/vlib/v/parser/expr.v
index b33622efc..3004125ed 100644
--- a/vlib/v/parser/expr.v
+++ b/vlib/v/parser/expr.v
@@ -449,7 +449,9 @@ fn (mut p Parser) check_expr(precedence int) !ast.Expr {
 					}
 				} else {
 					// Anonymous struct
-					p.next()
+					if !p.is_explicit_anon_struct_init() {
+						p.next()
+					}
 					return p.struct_init('', .anon, false)
 				}
 			} else if p.tok.kind == .key_type {
@@ -483,6 +485,24 @@ fn (mut p Parser) check_expr(precedence int) !ast.Expr {
 	return p.expr_with_left(node, precedence, is_stmt_ident)
 }
 
+fn (p &Parser) is_explicit_anon_struct_init() bool {
+	mut n := 2
+	mut curlies := 1
+	for curlies > 0 {
+		tok := p.peek_token(n)
+		if tok.kind == .eof {
+			return false
+		}
+		if tok.kind == .lcbr {
+			curlies++
+		} else if tok.kind == .rcbr {
+			curlies--
+		}
+		n++
+	}
+	return p.peek_token(n).kind == .lcbr
+}
+
 fn (mut p Parser) parse_typeof_expr(start_pos token.Pos) ast.Expr {
 	p.next() // typeof
 	if p.tok.kind == .lsbr {
diff --git a/vlib/v/tests/structs/anon_struct_local_init_test.v b/vlib/v/tests/structs/anon_struct_local_init_test.v
new file mode 100644
index 000000000..19976ba3f
--- /dev/null
+++ b/vlib/v/tests/structs/anon_struct_local_init_test.v
@@ -0,0 +1,12 @@
+fn test_anon_struct_as_local_variable() {
+	mut s := struct {
+		foo string
+		bar int
+	}{}
+	assert s.foo == ''
+	assert s.bar == 0
+	s.foo = 'foo'
+	s.bar = 1
+	assert s.foo == 'foo'
+	assert s.bar == 1
+}
-- 
2.39.5