From 0c9a3ca94a63ca82e76e67d58c1089a7ba1ad587 Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Wed, 25 Mar 2026 16:42:24 +0300
Subject: [PATCH] checker: fix clang build error with if expr in or block
 (fixes #15214)

---
 vlib/v/checker/if.v                     | 27 ++++++++++++-
 vlib/v/tests/if_expr_in_or_block_test.v | 52 +++++++++++++++++++++++++
 2 files changed, 77 insertions(+), 2 deletions(-)

diff --git a/vlib/v/checker/if.v b/vlib/v/checker/if.v
index b414dfd5e..c90519308 100644
--- a/vlib/v/checker/if.v
+++ b/vlib/v/checker/if.v
@@ -49,6 +49,18 @@ fn (mut c Checker) is_always_true_self_comparison(cond ast.Expr) bool {
 	return false
 }
 
+fn (c &Checker) is_interface_smartcast_sumtype_variant(expr ast.Expr, expected_type ast.Type, got_type ast.Type) bool {
+	sum_type := expected_type.clear_option_and_result()
+	if c.table.type_kind(sum_type) != .sum_type || !got_type.is_ptr() {
+		return false
+	}
+	if expr is ast.Ident && expr.obj is ast.Var {
+		return c.table.is_interface_var(expr.obj)
+			&& c.table.is_sumtype_or_in_variant(sum_type, got_type.deref())
+	}
+	return false
+}
+
 // gen_branch_context_string generate current branches context string.
 // context include generic types, `$for`.
 fn (mut c Checker) gen_branch_context_string() string {
@@ -476,6 +488,15 @@ fn (mut c Checker) if_expr(mut node ast.IfExpr) ast.Type {
 								}
 							}
 						}
+						if c.is_interface_smartcast_sumtype_variant(stmt.expr, former_expected_type,
+							stmt.typ)
+						{
+							node.is_expr = true
+							node.typ = former_expected_type.clear_option_and_result()
+							unsafe {
+								goto end_if
+							}
+						}
 						if node.is_expr && c.table.sym(former_expected_type).kind == .sum_type {
 							node.typ = former_expected_type
 							unsafe {
@@ -518,7 +539,8 @@ fn (mut c Checker) if_expr(mut node ast.IfExpr) ast.Type {
 					} else {
 						if !node.typ.has_option_or_result() && !node.typ.has_flag(.shared_f)
 							&& stmt.typ != ast.voidptr_type
-							&& stmt.typ.nr_muls() != node.typ.nr_muls() {
+							&& stmt.typ.nr_muls() != node.typ.nr_muls()
+							&& !c.is_interface_smartcast_sumtype_variant(stmt.expr, node.typ, stmt.typ) {
 							c.error('mismatched types `${c.table.type_to_str(node.typ)}` and `${c.table.type_to_str(stmt.typ)}`',
 								node.pos)
 						}
@@ -527,7 +549,8 @@ fn (mut c Checker) if_expr(mut node ast.IfExpr) ast.Type {
 							node.is_expr = true
 						}
 						if c.inside_assign && node.is_expr && !node.typ.has_flag(.shared_f)
-							&& stmt.typ != ast.voidptr_type {
+							&& stmt.typ != ast.voidptr_type
+							&& !c.is_interface_smartcast_sumtype_variant(stmt.expr, node.typ, stmt.typ) {
 							if stmt.typ.is_ptr() != node.typ.is_ptr() {
 								c.error('mismatched types `${c.table.type_to_str(node.typ)}` and `${c.table.type_to_str(stmt.typ)}`',
 									node.pos)
diff --git a/vlib/v/tests/if_expr_in_or_block_test.v b/vlib/v/tests/if_expr_in_or_block_test.v
index 77f91a11d..33b12452a 100644
--- a/vlib/v/tests/if_expr_in_or_block_test.v
+++ b/vlib/v/tests/if_expr_in_or_block_test.v
@@ -103,3 +103,55 @@ fn test_if_expr_with_multiple_branches_in_or_block() {
 	}
 	assert val == 1
 }
+
+struct IfExprEmptyReply {
+	value int
+}
+
+struct IfExprRedisError {
+	msg_ string
+}
+
+fn (e IfExprRedisError) msg() string {
+	return e.msg_
+}
+
+fn (e IfExprRedisError) code() int {
+	return 0
+}
+
+const if_expr_nil_reply = IfExprRedisError{'nil'}
+
+type IfExprReply = IfExprEmptyReply | IfExprRedisError
+
+fn if_expr_read_reply(msg string) !IfExprReply {
+	return IError(IfExprRedisError{msg})
+}
+
+fn if_expr_decode_reply(msg string) IfExprReply {
+	return if_expr_read_reply(msg) or {
+		if err is IfExprRedisError {
+			if err == if_expr_nil_reply {
+				IfExprEmptyReply{0}
+			} else {
+				err
+			}
+		} else {
+			panic(err)
+		}
+	}
+}
+
+fn test_if_expr_in_or_block_with_smartcasted_interface_sumtype_value() {
+	reply1 := if_expr_decode_reply('nil')
+	assert reply1 is IfExprEmptyReply
+	if reply1 is IfExprEmptyReply {
+		assert reply1.value == 0
+	}
+
+	reply2 := if_expr_decode_reply('x')
+	assert reply2 is IfExprRedisError
+	if reply2 is IfExprRedisError {
+		assert reply2.msg_ == 'x'
+	}
+}
-- 
2.39.5