Lint: Lint for std::for_each_n (#15093)

Signed-off-by: Kevin Baichoo <kbaichoo@google.com>

source/common/http/http2/codec_impl.cc

@@ -1409,8 +1409,13 @@ void ConnectionImpl::dumpState(std::ostream& os, int indent_level) const {
   DUMP_DETAILS(&protocol_constraints_);
 
   os << spaces << "Number of active streams: " << active_streams_.size() << " Active Streams:\n";
-  std::for_each_n(active_streams_.begin(), std::min<size_t>(active_streams_.size(), 100),
-                  [&](auto& stream) { DUMP_DETAILS(stream); });
+  size_t count = 0;
+  for (auto& stream : active_streams_) {
+    DUMP_DETAILS(stream);
+    if (++count >= 100) {
+      break;
+    }
+  }
 
   // Dump the active slice
   if (current_slice_ == nullptr) {

tools/code_format/check_format.py

@@ -155,6 +155,8 @@
 RELOADABLE_FLAG_REGEX = re.compile(".*(..)(envoy.reloadable_features.[^ ]*)\s.*")
 INVALID_REFLINK = re.compile(".* ref:.*")
 OLD_MOCK_METHOD_REGEX = re.compile("MOCK_METHOD\d")
+# C++17 feature, lacks sufficient support across various libraries / compilers.
+FOR_EACH_N_REGEX = re.compile("for_each_n\(")
 # Check for punctuation in a terminal ref clause, e.g.
 # :ref:`panic mode. <arch_overview_load_balancing_panic_threshold>`
 REF_WITH_PUNCTUATION_REGEX = re.compile(".*\. <[^<]*>`\s*")
@@ -779,6 +781,8 @@ def checkSourceLine(self, line, file_path, reportError):
       reportError("Test names should be CamelCase, starting with a capital letter")
     if OLD_MOCK_METHOD_REGEX.search(line):
       reportError("The MOCK_METHODn() macros should not be used, use MOCK_METHOD() instead")
+    if FOR_EACH_N_REGEX.search(line):
+      reportError("std::for_each_n should not be used, use an alternative for loop instead")
 
     if not self.allowlistedForSerializeAsString(file_path) and "SerializeAsString" in line:
       # The MessageLite::SerializeAsString doesn't generate deterministic serialization,

tools/code_format/check_format_test_helper.py

@@ -231,6 +231,7 @@ def runChecks():
   errors += checkUnfixableError("test_naming.cc",
                                 "Test names should be CamelCase, starting with a capital letter")
   errors += checkUnfixableError("mock_method_n.cc", "use MOCK_METHOD() instead")
+  errors += checkUnfixableError("for_each_n.cc", "use an alternative for loop instead")
   errors += checkUnfixableError(
       "test/register_factory.cc",
       "Don't use Registry::RegisterFactory or REGISTER_FACTORY in tests, use "

tools/testdata/check_format/for_each_n.cc

@@ -0,0 +1,10 @@
+#include <algorithm>
+#include <vector>
+namespace Envoy {
+
+void foo() {
+  std::vector<int> vec;
+  std::for_each_n(vec.begin(), 10, (int){});
+}
+
+} // namespace Envoy