From a80d668a52a92b67e01cdf59622454b31c4059c3 Mon Sep 17 00:00:00 2001
From: Victor Zverovich <viz@meta.com>
Date: Sat, 27 Jul 2024 09:54:40 -0700
Subject: [PATCH] Diagnose invalid precision

---
 include/fmt/base.h   | 42 ++++++++++++++++++++----------------------
 include/fmt/chrono.h | 14 ++++++++++----
 include/fmt/std.h    |  4 +++-
 test/format-test.cc  |  4 +++-
 4 files changed, 36 insertions(+), 28 deletions(-)

diff --git a/include/fmt/base.h b/include/fmt/base.h
index e29ff140..09668925 100644
--- a/include/fmt/base.h
+++ b/include/fmt/base.h
@@ -2323,7 +2323,7 @@ template <typename Char> struct dynamic_spec_id_handler {
   }
 };
 
-// Parses [integer | "{" [arg_id] "}"].
+// Parses integer | "{" [arg_id] "}".
 template <typename Char>
 FMT_CONSTEXPR auto parse_dynamic_spec(const Char* begin, const Char* end,
                                       int& value, arg_ref<Char>& ref,
@@ -2332,24 +2332,24 @@ FMT_CONSTEXPR auto parse_dynamic_spec(const Char* begin, const Char* end,
   FMT_ASSERT(begin != end, "");
   if ('0' <= *begin && *begin <= '9') {
     int val = parse_nonnegative_int(begin, end, -1);
-    if (val != -1)
-      value = val;
-    else
-      report_error("number is too big");
-  } else if (*begin == '{') {
-    ++begin;
-    if (begin != end) {
-      Char c = *begin;
-      if (c == '}' || c == ':') {
-        int id = ctx.next_arg_id();
-        ref = arg_ref<Char>(id);
-        ctx.check_dynamic_spec(id);
-      } else {
-        begin =
-            parse_arg_id(begin, end, dynamic_spec_id_handler<Char>{ctx, ref});
+    if (val == -1) report_error("number is too big");
+    value = val;
+  } else {
+    if (*begin == '{') {
+      ++begin;
+      if (begin != end) {
+        Char c = *begin;
+        if (c == '}' || c == ':') {
+          int id = ctx.next_arg_id();
+          ref = arg_ref<Char>(id);
+          ctx.check_dynamic_spec(id);
+        } else {
+          begin =
+              parse_arg_id(begin, end, dynamic_spec_id_handler<Char>{ctx, ref});
+        }
       }
+      if (begin != end && *begin == '}') return ++begin;
     }
-    if (begin != end && *begin == '}') return ++begin;
     report_error("invalid format string");
   }
   return begin;
@@ -2361,11 +2361,9 @@ FMT_CONSTEXPR auto parse_precision(const Char* begin, const Char* end,
                                    basic_format_parse_context<Char>& ctx)
     -> const Char* {
   ++begin;
-  if (begin == end || *begin == '}') {
-    report_error("invalid precision");
-    return begin;
-  }
-  return parse_dynamic_spec(begin, end, value, ref, ctx);
+  if (begin != end) begin = parse_dynamic_spec(begin, end, value, ref, ctx);
+  else report_error("invalid precision");
+  return begin;
 }
 
 enum class state { start, align, sign, hash, zero, width, precision, locale };
diff --git a/include/fmt/chrono.h b/include/fmt/chrono.h
index c01e4b14..76af8c24 100644
--- a/include/fmt/chrono.h
+++ b/include/fmt/chrono.h
@@ -2251,8 +2251,11 @@ struct formatter<std::chrono::duration<Rep, Period>, Char> {
     it = detail::parse_align(it, end, specs_);
     if (it == end) return it;
 
-    it = detail::parse_dynamic_spec(it, end, specs_.width, width_ref_, ctx);
-    if (it == end) return it;
+    Char c = *it;
+    if ((c >= '0' && c <= '9') || c == '{') {
+      it = detail::parse_dynamic_spec(it, end, specs_.width, width_ref_, ctx);
+      if (it == end) return it;
+    }
 
     auto checker = detail::chrono_format_checker();
     if (*it == '.') {
@@ -2410,8 +2413,11 @@ template <typename Char> struct formatter<std::tm, Char> {
     it = detail::parse_align(it, end, specs_);
     if (it == end) return it;
 
-    it = detail::parse_dynamic_spec(it, end, specs_.width, width_ref_, ctx);
-    if (it == end) return it;
+    Char c = *it;
+    if ((c >= '0' && c <= '9') || c == '{') {
+      it = detail::parse_dynamic_spec(it, end, specs_.width, width_ref_, ctx);
+      if (it == end) return it;
+    }
 
     end = detail::parse_chrono_format(it, end, detail::tm_format_checker());
     // Replace the default format_str only if the new spec is not empty.
diff --git a/include/fmt/std.h b/include/fmt/std.h
index fb43940b..0695460c 100644
--- a/include/fmt/std.h
+++ b/include/fmt/std.h
@@ -129,7 +129,9 @@ template <typename Char> struct formatter<std::filesystem::path, Char> {
     it = detail::parse_align(it, end, specs_);
     if (it == end) return it;
 
-    it = detail::parse_dynamic_spec(it, end, specs_.width, width_ref_, ctx);
+    Char c = *it;
+    if ((c >= '0' && c <= '9') || c == '{')
+      it = detail::parse_dynamic_spec(it, end, specs_.width, width_ref_, ctx);
     if (it != end && *it == '?') {
       debug_ = true;
       ++it;
diff --git a/test/format-test.cc b/test/format-test.cc
index a018b9f7..86c70981 100644
--- a/test/format-test.cc
+++ b/test/format-test.cc
@@ -945,7 +945,7 @@ TEST(format_test, precision) {
   EXPECT_THROW_MSG((void)fmt::format(runtime("{0:."), 0.0), format_error,
                    "invalid precision");
   EXPECT_THROW_MSG((void)fmt::format(runtime("{0:.}"), 0.0), format_error,
-                   "invalid precision");
+                   "invalid format string");
 
   EXPECT_THROW_MSG((void)fmt::format(runtime("{0:.2"), 0), format_error,
                    "invalid format specifier");
@@ -1066,6 +1066,8 @@ TEST(format_test, precision) {
   EXPECT_THROW_MSG(
       (void)fmt::format("{:.2147483646f}", -2.2121295195081227E+304),
       format_error, "number is too big");
+  EXPECT_THROW_MSG((void)fmt::format(runtime("{:.f}"), 42.0), format_error,
+                   "invalid format string");
 
   EXPECT_EQ(fmt::format("{0:.2}", "str"), "st");
   EXPECT_EQ(fmt::format("{0:.5}", "вожыкі"), "вожык");