Handle nested braces in join (#638)

fmt/format.h

@@ -4111,10 +4111,14 @@ template <typename ArgFormatter, typename Char, typename It>
 void format_arg(fmt::BasicFormatter<Char, ArgFormatter> &f,
     const Char *&format_str, const ArgJoin<Char, It>& e) {
   const Char* end = format_str;
-  if (*end == ':')
-    ++end;
-  while (*end && *end != '}')
+  int brace_level = 1;
+  while (*end) {
+    if (*end == '}' && --brace_level == 0)
+      break;
+    if (*end == '{')
+      ++brace_level;
     ++end;
+  }
   if (*end != '}')
     FMT_THROW(FormatError("missing '}' in format string"));
 

test/format-test.cc

@@ -1611,13 +1611,15 @@ TEST(FormatTest, JoinArg) {
   v2.push_back(1.2f);
   v2.push_back(3.4f);
 
-  EXPECT_EQ("(1, 2, 3)", format("({})", join(v1 + 0, v1 + 3, ", ")));
-  EXPECT_EQ("(1)", format("({})", join(v1 + 0, v1 + 1, ", ")));
-  EXPECT_EQ("()", format("({})", join(v1 + 0, v1 + 0, ", ")));
-  EXPECT_EQ("(001, 002, 003)", format("({:03})", join(v1 + 0, v1 + 3, ", ")));
-  EXPECT_EQ("(+01.20, +03.40)", format("({:+06.2f})", join(v2.begin(), v2.end(), ", ")));
-
-  EXPECT_EQ(L"(1, 2, 3)", format(L"({})", join(v1 + 0, v1 + 3, L", ")));
+  EXPECT_EQ("(1, 2, 3)", format("({})", join(v1, v1 + 3, ", ")));
+  EXPECT_EQ("(1)", format("({})", join(v1, v1 + 1, ", ")));
+  EXPECT_EQ("()", format("({})", join(v1, v1, ", ")));
+  EXPECT_EQ("(001, 002, 003)", format("({:03})", join(v1, v1 + 3, ", ")));
+  EXPECT_EQ("(+01.20, +03.40)",
+            format("({:+06.2f})", join(v2.begin(), v2.end(), ", ")));
+
+  EXPECT_EQ(L"(1, 2, 3)", format(L"({})", join(v1, v1 + 3, L", ")));
+  EXPECT_EQ("1, 2, 3", format("{0:{1}}", join(v1, v1 + 3, ", "), 1)); 
 
 #if FMT_HAS_GXX_CXX11
   EXPECT_EQ("(1, 2, 3)", format("({})", join(v1, ", ")));