From 74343496d7435a303d4aaed5a01a69918f5ea175 Mon Sep 17 00:00:00 2001
From: Yat Ho <lagoho7@gmail.com>
Date: Thu, 25 Jun 2026 01:01:32 +0800
Subject: [PATCH] fix: explicitly check `operator[]` in `is_contiguous`

Prevent false positives when the container itself does not have `operator[](size_t)`, but the target type of one of the non-explicit user-defined conversion functions does.
---
 include/fmt/base.h | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/include/fmt/base.h b/include/fmt/base.h
index 5d0241c8..60d1b792 100644
--- a/include/fmt/base.h
+++ b/include/fmt/base.h
@@ -493,9 +493,10 @@ inline FMT_CONSTEXPR auto get_container(OutputIt it) ->
 template <typename T, typename Enable = void>
 struct is_contiguous : std::false_type {};
 template <typename T>
-struct is_contiguous<T, void_t<decltype(std::declval<T&>().data()),
-                               decltype(std::declval<T&>().size()),
-                               decltype(std::declval<T&>()[size_t()])>>
+struct is_contiguous<T,
+                     void_t<decltype(std::declval<T&>().data()),
+                            decltype(std::declval<T&>().size()),
+                            decltype(std::declval<T&>().operator[](size_t()))>>
     : std::true_type {};
 }  // namespace detail