From b4b1657c2aa45cf08dcd7a76e2302bef60314148 Mon Sep 17 00:00:00 2001
From: Satyakam Mishra <mishra.satyakam03@gmail.com>
Date: Fri, 4 Sep 2026 16:17:58 +0000
Subject: [PATCH] Fix debug format width calculation (#4902)

---
 include/fmt/format.h | 27 ++++++++++++++++++++++-----
 test/format-test.cc  |  2 ++
 2 files changed, 24 insertions(+), 5 deletions(-)

diff --git a/include/fmt/format.h b/include/fmt/format.h
index 5fe8f47a..2cd380b5 100644
--- a/include/fmt/format.h
+++ b/include/fmt/format.h
@@ -2069,11 +2069,22 @@ template <typename Char, typename OutputIt>
 FMT_CONSTEXPR auto write_char(OutputIt out, Char value,
                               const format_specs& specs) -> OutputIt {
   bool is_debug = specs.type() == presentation_type::debug;
-  return write_padded<Char>(out, specs, 1, [=](reserve_iterator<OutputIt> it) {
-    if (is_debug) return write_escaped_char(it, value);
-    *it++ = value;
-    return it;
-  });
+  Char buf[12];
+  auto* begin = buf;
+  auto* end = begin;
+  size_t size = 1;
+
+  if (is_debug) {
+    end = write_escaped_char(begin, value);
+    size = to_unsigned(end - begin);
+  }
+
+  return write_padded<Char>(out, specs, size,
+                            [=](reserve_iterator<OutputIt> it) {
+                              if (is_debug) return copy<Char>(begin, end, it);
+                              *it++ = value;
+                              return it;
+                            });
 }
 
 template <typename Char> class digit_grouping {
@@ -2431,6 +2442,12 @@ FMT_CONSTEXPR auto write(OutputIt out, basic_string_view<Char> s,
     return false;
   });
 
+  if (is_debug && s.size() == 0 && specs.precision != 0 &&
+      display_width < display_width_limit) {
+    ++display_width;
+    ++size;
+  }
+
   struct bounded_output_iterator {
     reserve_iterator<OutputIt> underlying_iterator;
     size_t bound;
diff --git a/test/format-test.cc b/test/format-test.cc
index f944649d..772ecb09 100644
--- a/test/format-test.cc
+++ b/test/format-test.cc
@@ -1006,6 +1006,7 @@ TEST(format_test, width) {
 
 TEST(format_test, debug_presentation) {
   EXPECT_EQ(fmt::format("{:?}", ""), R"("")");
+  EXPECT_EQ(fmt::format("{:1?}", ""), R"("")");
 
   EXPECT_EQ(fmt::format("{:*<5.0?}", "\n"), R"(*****)");
   EXPECT_EQ(fmt::format("{:*<5.1?}", "\n"), R"("****)");
@@ -1748,6 +1749,7 @@ TEST(format_test, format_char) {
 
   EXPECT_EQ(fmt::format("{}", '\n'), "\n");
   EXPECT_EQ(fmt::format("{:?}", '\n'), "'\\n'");
+  EXPECT_EQ(fmt::format("{:6?}", 'a'), "'a'   ");
   EXPECT_EQ(fmt::format("{:x}", '\xff'), "ff");
 }