Fix exception propagation from iterators (#2097)

fmtlib · Jan 24, 2021 · ce519e9 · ce519e9
1 parent acef0bb
commit ce519e9
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Showing 2 changed files with 13 additions and 1 deletion.
diff --git a/include/fmt/format.h b/include/fmt/format.h
@@ -658,8 +658,9 @@ void buffer<T>::append(const U* begin, const U* end) {
 
 template <typename OutputIt, typename T, typename Traits>
 void iterator_buffer<OutputIt, T, Traits>::flush() {
-  out_ = copy_str<T>(data_, data_ + this->limit(this->size()), out_);
+  auto size = this->size();
   this->clear();
+  out_ = copy_str<T>(data_, data_ + this->limit(size), out_);
 }
 }  // namespace detail
 

diff --git a/test/format-test.cc b/test/format-test.cc
@@ -2021,6 +2021,17 @@ TEST(FormatTest, FormatTo) {
   EXPECT_EQ(string_view(v.data(), v.size()), "foo");
 }
 
+struct nongrowing_container {
+  using value_type = char;
+  void push_back(char) { throw std::runtime_error("can't take it any more"); }
+};
+
+TEST(FormatTest, FormatToPropagatesExceptions) {
+  auto c = nongrowing_container();
+  EXPECT_THROW(fmt::format_to(std::back_inserter(c), "{}", 42),
+               std::runtime_error);
+}
+
 TEST(FormatTest, FormatToN) {
   char buffer[4];
   buffer[3] = 'x';