From 32ad8de8a4347b85954f526f4890f0450fd9796e Mon Sep 17 00:00:00 2001
From: Felipe Pena <felipensp@gmail.com>
Date: Sat, 25 Oct 2025 17:24:49 -0300
Subject: [PATCH] checker: fix comptime else branch handling (fix #25586)
 (#25589)

---
 vlib/v/checker/if.v                           | 46 ++++++++++++++-----
 vlib/v/gen/c/testdata/comptime_if.c.must_have |  9 ++++
 vlib/v/gen/c/testdata/comptime_if.vv          | 10 ++++
 3 files changed, 53 insertions(+), 12 deletions(-)
 create mode 100644 vlib/v/gen/c/testdata/comptime_if.c.must_have
 create mode 100644 vlib/v/gen/c/testdata/comptime_if.vv

diff --git a/vlib/v/checker/if.v b/vlib/v/checker/if.v
index b61e0b1d9..d387c616c 100644
--- a/vlib/v/checker/if.v
+++ b/vlib/v/checker/if.v
@@ -308,7 +308,9 @@ fn (mut c Checker) if_expr(mut node ast.IfExpr) ast.Type {
 							node.is_expr = true
 							node.typ = c.unwrap_generic(c.expected_type)
 						}
-						continue
+						unsafe {
+							goto end_if
+						}
 					}
 					if c.expected_expr_type != ast.void_type {
 						c.expected_type = c.expected_expr_type
@@ -327,7 +329,9 @@ fn (mut c Checker) if_expr(mut node ast.IfExpr) ast.Type {
 						// (e.g. argument expression, variable declaration / assignment)
 						c.error('the final expression in `if` or `match`, must have a value of a non-void type',
 							stmt.pos)
-						continue
+						unsafe {
+							goto end_if
+						}
 					}
 					if !c.check_types(stmt.typ, node.typ) {
 						if node.typ == ast.void_type {
@@ -339,37 +343,51 @@ fn (mut c Checker) if_expr(mut node ast.IfExpr) ast.Type {
 								node.typ = stmt.typ
 							}
 							c.expected_expr_type = node.typ
-							continue
+							unsafe {
+								goto end_if
+							}
 						} else if node.typ in [ast.float_literal_type, ast.int_literal_type] {
 							if node.typ == ast.int_literal_type {
 								if stmt.typ.is_int() || stmt.typ.is_float() {
 									node.typ = stmt.typ
-									continue
+									unsafe {
+										goto end_if
+									}
 								}
 							} else { // node.typ == float_literal
 								if stmt.typ.is_float() {
 									node.typ = stmt.typ
-									continue
+									unsafe {
+										goto end_if
+									}
 								}
 							}
 						}
 						if stmt.typ in [ast.float_literal_type, ast.int_literal_type] {
 							if stmt.typ == ast.int_literal_type {
 								if node.typ.is_int() || node.typ.is_float() {
-									continue
+									unsafe {
+										goto end_if
+									}
 								}
 							} else { // expr_type == float_literal
 								if node.typ.is_float() {
-									continue
+									unsafe {
+										goto end_if
+									}
 								}
 							}
 						}
 						if node.is_expr && c.table.sym(former_expected_type).kind == .sum_type {
 							node.typ = former_expected_type
-							continue
+							unsafe {
+								goto end_if
+							}
 						}
 						if is_noreturn_callexpr(stmt.expr) {
-							continue
+							unsafe {
+								goto end_if
+							}
 						}
 						if (node.typ.has_option_or_result())
 							&& c.table.sym(stmt.typ).kind == .struct
@@ -382,7 +400,9 @@ fn (mut c Checker) if_expr(mut node ast.IfExpr) ast.Type {
 								pos:       node.pos
 							}
 							stmt.typ = ast.error_type
-							continue
+							unsafe {
+								goto end_if
+							}
 						}
 						if (node.typ == ast.none_type && stmt.typ != ast.none_type)
 							|| (stmt.typ == ast.none_type && node.typ != ast.none_type) {
@@ -391,7 +411,9 @@ fn (mut c Checker) if_expr(mut node ast.IfExpr) ast.Type {
 							} else {
 								node.typ.set_flag(.option)
 							}
-							continue
+							unsafe {
+								goto end_if
+							}
 						}
 						c.error('mismatched types `${c.table.type_to_str(node.typ)}` and `${c.table.type_to_str(stmt.typ)}`',
 							node.pos)
@@ -440,7 +462,7 @@ fn (mut c Checker) if_expr(mut node ast.IfExpr) ast.Type {
 				nbranches_without_return++
 			}
 		}
-
+		end_if:
 		if comptime_remove_curr_branch_stmts && !c.pref.output_cross_c {
 			// remove the branch statements since they may contain OS-specific code.
 			branch.stmts = []
diff --git a/vlib/v/gen/c/testdata/comptime_if.c.must_have b/vlib/v/gen/c/testdata/comptime_if.c.must_have
new file mode 100644
index 000000000..761452fe9
--- /dev/null
+++ b/vlib/v/gen/c/testdata/comptime_if.c.must_have
@@ -0,0 +1,9 @@
+string _t1;
+#if defined(CUSTOM_DEFINE_some_custom_define)
+#elif defined(CUSTOM_DEFINE_some_other_define)
+		_t1 = _S("xyz");
+		;
+#else
+#endif
+		string platform = _t1;
+builtin__println(platform);
\ No newline at end of file
diff --git a/vlib/v/gen/c/testdata/comptime_if.vv b/vlib/v/gen/c/testdata/comptime_if.vv
new file mode 100644
index 000000000..5e69041b7
--- /dev/null
+++ b/vlib/v/gen/c/testdata/comptime_if.vv
@@ -0,0 +1,10 @@
+// vtest vflags: -d some_other_define
+platform := $if some_custom_define ? {
+	'abc'
+} $else $if some_other_define ? {
+	'xyz'
+} $else {
+	eprintln('oh no')
+	exit(1)
+}
+println(platform)
-- 
2.39.5