From 439eceb5ce67003141d2d2be84adb01659380f59 Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Tue, 21 Apr 2026 05:50:04 +0300
Subject: [PATCH] checker: support $for variant in field.typ.variants for
 sumtype fields (fixes #26902)

---
 vlib/v/checker/comptime.v                     |  9 ++++++-
 vlib/v/fmt/fmt.v                              |  9 ++++---
 vlib/v/gen/c/comptime.v                       |  8 +++++-
 vlib/v/parser/comptime.v                      | 25 +++++++++++++++++--
 vlib/v/tests/comptime/comptime_variant_test.v | 25 +++++++++++++++++++
 5 files changed, 68 insertions(+), 8 deletions(-)

diff --git a/vlib/v/checker/comptime.v b/vlib/v/checker/comptime.v
index b85bf30a7..461f3d004 100644
--- a/vlib/v/checker/comptime.v
+++ b/vlib/v/checker/comptime.v
@@ -414,7 +414,7 @@ fn (mut c Checker) comptime_selector(mut node ast.ComptimeSelector) ast.Type {
 }
 
 fn (mut c Checker) comptime_for(mut node ast.ComptimeFor) {
-	typ := if node.expr !is ast.EmptyExpr {
+	mut typ := if node.expr !is ast.EmptyExpr {
 		node.typ = c.expr(mut node.expr)
 		c.unwrap_generic(node.typ)
 	} else if node.typ != ast.void_type {
@@ -423,6 +423,13 @@ fn (mut c Checker) comptime_for(mut node ast.ComptimeFor) {
 		node.typ = c.expr(mut node.expr)
 		c.unwrap_generic(node.typ)
 	}
+	if node.expr !is ast.EmptyExpr {
+		resolved_typ := c.type_resolver.get_type(node.expr)
+		if resolved_typ != ast.void_type {
+			node.typ = resolved_typ
+			typ = c.unwrap_generic(node.typ)
+		}
+	}
 	sym := if node.typ != c.field_data_type {
 		c.table.final_sym(typ)
 	} else {
diff --git a/vlib/v/fmt/fmt.v b/vlib/v/fmt/fmt.v
index 086f95ca3..3ccf79612 100644
--- a/vlib/v/fmt/fmt.v
+++ b/vlib/v/fmt/fmt.v
@@ -941,12 +941,13 @@ pub fn (mut f Fmt) branch_stmt(node ast.BranchStmt) {
 }
 
 pub fn (mut f Fmt) comptime_for(node ast.ComptimeFor) {
-	typ := if node.typ != ast.void_type {
-		f.no_cur_mod(f.type_to_str_using_aliases(node.typ, f.mod2alias))
+	f.write('\$for ${node.val_var} in ')
+	if node.typ != ast.void_type {
+		f.write(f.no_cur_mod(f.type_to_str_using_aliases(node.typ, f.mod2alias)))
 	} else {
-		(node.expr as ast.Ident).name
+		f.expr(node.expr)
 	}
-	f.write('\$for ${node.val_var} in ${typ}.${node.kind.str()} {')
+	f.write('.${node.kind.str()} {')
 	if node.stmts.len > 0 || node.pos.line_nr < node.pos.last_line {
 		f.writeln('')
 		f.stmts(node.stmts)
diff --git a/vlib/v/gen/c/comptime.v b/vlib/v/gen/c/comptime.v
index 9cc1885a0..a49dfe333 100644
--- a/vlib/v/gen/c/comptime.v
+++ b/vlib/v/gen/c/comptime.v
@@ -903,7 +903,13 @@ fn (mut g Gen) pop_comptime_info() {
 
 fn (mut g Gen) comptime_for(node ast.ComptimeFor) {
 	resolved_typ := if node.expr !is ast.EmptyExpr {
-		g.unwrap_generic(g.recheck_concrete_type(g.resolved_expr_type(node.expr, node.typ)))
+		mut expr_typ := g.unwrap_generic(g.recheck_concrete_type(g.resolved_expr_type(node.expr,
+			node.typ)))
+		resolved_ct_typ := g.type_resolver.get_type(node.expr)
+		if resolved_ct_typ != ast.void_type {
+			expr_typ = g.unwrap_generic(g.recheck_concrete_type(resolved_ct_typ))
+		}
+		expr_typ
 	} else if node.typ != g.field_data_type {
 		g.unwrap_generic(node.typ)
 	} else {
diff --git a/vlib/v/parser/comptime.v b/vlib/v/parser/comptime.v
index 658613bab..50cf7b607 100644
--- a/vlib/v/parser/comptime.v
+++ b/vlib/v/parser/comptime.v
@@ -11,10 +11,17 @@ import v.util
 
 const supported_comptime_calls = ['html', 'tmpl', 'env', 'embed_file', 'pkgconfig', 'compile_error',
 	'compile_warn', 'd', 'res']
+const supported_comptime_for_kinds = ['methods', 'fields', 'values', 'variants', 'attributes',
+	'params']
 const comptime_types = ['map', 'array', 'array_dynamic', 'array_fixed', 'int', 'float', 'struct',
 	'interface', 'enum', 'sumtype', 'alias', 'function', 'option', 'shared', 'string', 'pointer',
 	'voidptr']
 
+@[inline]
+fn is_supported_comptime_for_kind(name string) bool {
+	return name in supported_comptime_for_kinds
+}
+
 fn (mut p Parser) parse_comptime_type() ast.ComptimeType {
 	pos := p.tok.pos()
 	p.check(.dollar)
@@ -538,6 +545,7 @@ fn (mut p Parser) comptime_for() ast.ComptimeFor {
 	// `$for field in App.fields {`
 	// `$for attr in App.attributes {`
 	// `$for variant in App.variants {`
+	// `$for variant in field.typ.variants {`
 	p.next()
 	p.check(.key_for)
 	var_pos := p.tok.pos()
@@ -555,8 +563,21 @@ fn (mut p Parser) comptime_for() ast.ComptimeFor {
 	if p.tok.lit[0].is_capital() || p.tok.lit in p.imports {
 		typ = p.parse_any_type(lang, false, true, false)
 	} else {
-		expr = p.ident(lang)
-		p.scope.mark_var_as_used((expr as ast.Ident).name)
+		mut selector_expr := ast.Expr(p.ident(lang))
+		p.scope.mark_var_as_used((selector_expr as ast.Ident).name)
+		for p.tok.kind == .dot && p.peek_tok.kind == .name
+			&& !is_supported_comptime_for_kind(p.peek_tok.lit) {
+			selector_expr = p.dot_expr(selector_expr)
+			if p.name_error {
+				return ast.ComptimeFor{}
+			}
+			if selector_expr !is ast.SelectorExpr {
+				p.error_with_pos('invalid expr, use a selector like `field.typ`',
+					selector_expr.pos())
+				return ast.ComptimeFor{}
+			}
+		}
+		expr = selector_expr
 	}
 	typ_pos = typ_pos.extend(p.prev_tok.pos())
 	p.check(.dot)
diff --git a/vlib/v/tests/comptime/comptime_variant_test.v b/vlib/v/tests/comptime/comptime_variant_test.v
index f87e3ae2b..dbf7ced93 100644
--- a/vlib/v/tests/comptime/comptime_variant_test.v
+++ b/vlib/v/tests/comptime/comptime_variant_test.v
@@ -20,3 +20,28 @@ fn test_main() {
 	a := TestSum(123)
 	gen(a)
 }
+
+type FieldVariantsMixed = []bool | []int | []string | string
+
+struct FieldVariantsHolder {
+mut:
+	t FieldVariantsMixed
+}
+
+fn enumerate_sumtype_field_variants[T]() int {
+	mut count := 0
+	$for field in T.fields {
+		$if field.typ is $sumtype {
+			$for variant in field.typ.variants {
+				if typeof(variant.typ).name != '' {
+					count++
+				}
+			}
+		}
+	}
+	return count
+}
+
+fn test_comptime_for_field_typ_variants() {
+	assert enumerate_sumtype_field_variants[FieldVariantsHolder]() == 4
+}
-- 
2.39.5