From 7270d5439e5d2a0f87c33ec8b423b2eddf953d7a Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Wed, 15 Apr 2026 15:17:33 +0300
Subject: [PATCH] checker: fix nested `if` expression causing compilation error
 (fixes #26865)

---
 vlib/v/ast/ast.v                                 | 11 ++++++-----
 vlib/v/checker/if.v                              |  2 +-
 vlib/v/parser/expr.v                             | 15 +++++++++++++++
 vlib/v/tests/conditions/ifs/if_expression_test.v | 10 ++++++++++
 4 files changed, 32 insertions(+), 6 deletions(-)

diff --git a/vlib/v/ast/ast.v b/vlib/v/ast/ast.v
index e8e49f255..dfff71d53 100644
--- a/vlib/v/ast/ast.v
+++ b/vlib/v/ast/ast.v
@@ -1337,11 +1337,12 @@ pub:
 	pos           token.Pos
 	post_comments []Comment
 pub mut:
-	left     Expr       // `a` in `a := if ...`
-	branches []IfBranch // includes all `else if` branches
-	is_expr  bool
-	typ      Type
-	has_else bool
+	left       Expr       // `a` in `a := if ...`
+	branches   []IfBranch // includes all `else if` branches
+	is_expr    bool
+	force_expr bool
+	typ        Type
+	has_else   bool
 	// implements bool // comptime $if implements interface
 }
 
diff --git a/vlib/v/checker/if.v b/vlib/v/checker/if.v
index df4e6fc8e..84912eacd 100644
--- a/vlib/v/checker/if.v
+++ b/vlib/v/checker/if.v
@@ -127,7 +127,7 @@ fn (mut c Checker) if_expr(mut node ast.IfExpr) ast.Type {
 	if c.expected_type == ast.void_type && node_is_expr {
 		c.expected_type = c.expected_or_type
 	}
-	expr_required := c.expected_type != ast.void_type
+	expr_required := node.force_expr || c.expected_type != ast.void_type
 		|| (node.is_comptime && node.is_expr && node.has_else && c.fn_level > 0)
 	former_expected_type := c.expected_type
 	if node_is_expr {
diff --git a/vlib/v/parser/expr.v b/vlib/v/parser/expr.v
index 3dbd07cbf..09daa1292 100644
--- a/vlib/v/parser/expr.v
+++ b/vlib/v/parser/expr.v
@@ -668,6 +668,7 @@ fn (mut p Parser) expr_with_left(left ast.Expr, precedence int, is_stmt_ident bo
 	for {
 		if p.tok.kind == .lpar && p.tok.line_nr == p.prev_tok.line_nr
 			&& node in [ast.CallExpr, ast.IndexExpr, ast.SelectorExpr] {
+			p.promote_if_expr_to_value(mut node)
 			node = p.call_expr_with_left(node)
 			p.is_stmt_ident = is_stmt_ident
 			continue
@@ -681,6 +682,7 @@ fn (mut p Parser) expr_with_left(left ast.Expr, precedence int, is_stmt_ident bo
 				&& p.tok.pos - p.prev_tok.pos > p.prev_tok.len {
 				return node
 			}
+			p.promote_if_expr_to_value(mut node)
 			node = p.dot_expr(node)
 			if p.name_error {
 				return node
@@ -689,6 +691,7 @@ fn (mut p Parser) expr_with_left(left ast.Expr, precedence int, is_stmt_ident bo
 		} else if left !is ast.IntegerLiteral && p.tok.kind in [.lsbr, .nilsbr]
 			&& (p.tok.line_nr == p.prev_tok.line_nr || (p.prev_tok.kind == .string
 			&& p.tok.line_nr == p.prev_tok.line_nr + p.prev_tok.lit.count('\n'))) {
+			p.promote_if_expr_to_value(mut node)
 			if p.peek_tok.kind == .question && p.peek_token(2).kind == .name {
 				p.next()
 				p.error_with_pos('cannot use Option type name as concrete type', p.tok.pos())
@@ -702,6 +705,7 @@ fn (mut p Parser) expr_with_left(left ast.Expr, precedence int, is_stmt_ident bo
 			// sum type as cast `x := SumType as Variant`
 			if !p.inside_asm {
 				pos := p.tok.pos()
+				p.promote_if_expr_to_value(mut node)
 				p.next()
 				typ := p.parse_type()
 				node = ast.AsCast{
@@ -736,6 +740,7 @@ fn (mut p Parser) expr_with_left(left ast.Expr, precedence int, is_stmt_ident bo
 			&& !(p.tok.kind in [.minus, .amp, .mul, .arrow, .key_as, .key_in, .key_is]
 			&& p.tok.line_nr != p.prev_tok.line_nr) {
 			// continue on infix expr
+			p.promote_if_expr_to_value(mut node)
 			node = p.infix_expr(node)
 			// return early `if bar is SumType as b {`
 			if p.tok.kind == .key_as && p.inside_if {
@@ -801,6 +806,16 @@ fn (mut p Parser) expr_with_left(left ast.Expr, precedence int, is_stmt_ident bo
 	return node
 }
 
+fn (mut p Parser) promote_if_expr_to_value(mut expr ast.Expr) {
+	match mut expr {
+		ast.IfExpr {
+			expr.is_expr = true
+			expr.force_expr = true
+		}
+		else {}
+	}
+}
+
 fn (mut p Parser) call_expr_with_left(left ast.Expr) ast.CallExpr {
 	p.next()
 	pos := p.tok.pos()
diff --git a/vlib/v/tests/conditions/ifs/if_expression_test.v b/vlib/v/tests/conditions/ifs/if_expression_test.v
index 9287fd547..8d13b16ed 100644
--- a/vlib/v/tests/conditions/ifs/if_expression_test.v
+++ b/vlib/v/tests/conditions/ifs/if_expression_test.v
@@ -170,6 +170,16 @@ fn test_multi_if_expr_with_infix() {
 	assert a == 7
 }
 
+fn test_nested_if_expr_with_infix_in_branch() {
+	a := if false { 0 } else { if false { 2 } else { 3 } + 4
+	 } + 5
+	assert a == 12
+
+	b := if false { 'a' } else { if false { 'c' } else { 'd' } + 'e'
+	 } + 'f'
+	assert b == 'def'
+}
+
 fn test_if_expr_with_array_map() {
 	num_string := '2 3'
 
-- 
2.39.5