Compiler warnings make test-linux workflow fail on v14.x

[targos]

For example: https://github.com/nodejs/node/runs/2607695302?check_suite_focus=true

Some notes:

• We do not see these warnings on master
• --error-on-warn was backported to v14.3.0 so this is probably a regression in one of the commits that were backported to v14.17.

[targos]

../src/node_buffer.cc: In function ‘void node::Buffer::{anonymous}::StringWrite(const v8::FunctionCallbackInfo<v8::Value>&) [with node::encoding encoding = node::UTF8]’:
../src/node_buffer.cc:665:3: error: ‘offset’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
  665 |   if (offset > ts_obj_length) {
      |   ^~
../src/node_buffer.cc:662:10: error: ‘max_length’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
  662 |   size_t max_length;
      |          ^~~~~~~~~~
../src/node_buffer.cc: In function ‘void node::Buffer::{anonymous}::StringWrite(const v8::FunctionCallbackInfo<v8::Value>&) [with node::encoding encoding = node::ASCII]’:
../src/node_buffer.cc:665:3: error: ‘offset’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
  665 |   if (offset > ts_obj_length) {
      |   ^~
../src/node_buffer.cc:662:10: error: ‘max_length’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
  662 |   size_t max_length;
      |          ^~~~~~~~~~
../src/node_buffer.cc: In function ‘void node::Buffer::{anonymous}::StringWrite(const v8::FunctionCallbackInfo<v8::Value>&) [with node::encoding encoding = node::BASE64]’:
../src/node_buffer.cc:665:3: error: ‘offset’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
  665 |   if (offset > ts_obj_length) {
      |   ^~
../src/node_buffer.cc: In function ‘void node::Buffer::{anonymous}::StringWrite(const v8::FunctionCallbackInfo<v8::Value>&) [with node::encoding encoding = node::BINARY]’:
../src/node_buffer.cc:665:3: error: ‘offset’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
  665 |   if (offset > ts_obj_length) {
      |   ^~
../src/node_buffer.cc: In function ‘void node::Buffer::{anonymous}::StringWrite(const v8::FunctionCallbackInfo<v8::Value>&) [with node::encoding encoding = node::HEX]’:
../src/node_buffer.cc:665:3: error: ‘offset’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
  665 |   if (offset > ts_obj_length) {
      |   ^~
../src/node_buffer.cc:662:10: error: ‘max_length’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
  662 |   size_t max_length;
      |          ^~~~~~~~~~
../src/node_buffer.cc: In function ‘void node::Buffer::{anonymous}::StringWrite(const v8::FunctionCallbackInfo<v8::Value>&) [with node::encoding encoding = node::UCS2]’:
../src/node_buffer.cc:665:3: error: ‘offset’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
  665 |   if (offset > ts_obj_length) {
      |   ^~
cc1plus: all warnings being treated as errors
make[2]: *** [libnode.target.mk:345: /home/runner/work/node/node/out/Release/obj.target/libnode/src/node_buffer.o] Error 1
make[2]: *** Waiting for unfinished jobs....

[richardlau]

I see similar errors locally (Fedora 33 with gcc/g++ 10) with master.

../src/node_buffer.cc: In function ‘void node::Buffer::{anonymous}::Fill(const v8::FunctionCallbackInfo<v8::Value>&)’:
../src/node_buffer.cc:646:35: error: ‘start’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
  646 |   char* ptr = ts_obj_data + start + str_length;
      |               ~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~
../src/node_buffer.cc: In function ‘void node::Buffer::{anonymous}::StringWrite(const v8::FunctionCallbackInfo<v8::Value>&) [with node::encoding encoding = node::ASCII]’:
../src/node_buffer.cc:675:3: error: ‘offset’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
  675 |   if (offset > ts_obj_length) {
      |   ^~
../src/node_buffer.cc: In function ‘void node::Buffer::{anonymous}::StringWrite(const v8::FunctionCallbackInfo<v8::Value>&) [with node::encoding encoding = node::BASE64]’:
../src/node_buffer.cc:675:3: error: ‘offset’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
  675 |   if (offset > ts_obj_length) {
      |   ^~
../src/node_buffer.cc: In function ‘void node::Buffer::{anonymous}::StringWrite(const v8::FunctionCallbackInfo<v8::Value>&) [with node::encoding encoding = node::BASE64URL]’:
../src/node_buffer.cc:675:3: error: ‘offset’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
  675 |   if (offset > ts_obj_length) {
      |   ^~
../src/node_buffer.cc:672:10: error: ‘max_length’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
  672 |   size_t max_length;
      |          ^~~~~~~~~~
../src/node_buffer.cc: In function ‘void node::Buffer::{anonymous}::StringWrite(const v8::FunctionCallbackInfo<v8::Value>&) [with node::encoding encoding = node::BINARY]’:
../src/node_buffer.cc:675:3: error: ‘offset’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
  675 |   if (offset > ts_obj_length) {
      |   ^~
../src/node_buffer.cc:672:10: error: ‘max_length’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
  672 |   size_t max_length;
      |          ^~~~~~~~~~
../src/node_buffer.cc: In function ‘void node::Buffer::{anonymous}::StringWrite(const v8::FunctionCallbackInfo<v8::Value>&) [with node::encoding encoding = node::HEX]’:
../src/node_buffer.cc:675:3: error: ‘offset’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
  675 |   if (offset > ts_obj_length) {
      |   ^~
../src/node_buffer.cc: In function ‘void node::Buffer::{anonymous}::StringWrite(const v8::FunctionCallbackInfo<v8::Value>&) [with node::encoding encoding = node::UCS2]’:
../src/node_buffer.cc:675:3: error: ‘offset’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
  675 |   if (offset > ts_obj_length) {
      |   ^~
../src/node_buffer.cc:672:10: error: ‘max_length’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
  672 |   size_t max_length;
      |          ^~~~~~~~~~
../src/node_buffer.cc: In function ‘void node::Buffer::{anonymous}::StringWrite(const v8::FunctionCallbackInfo<v8::Value>&) [with node::encoding encoding = node::UTF8]’:
../src/node_buffer.cc:675:3: error: ‘offset’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
  675 |   if (offset > ts_obj_length) {
      |   ^~
../src/node_buffer.cc:672:10: error: ‘max_length’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
  672 |   size_t max_length;
      |          ^~~~~~~~~~
cc1plus: all warnings being treated as errors

[targos]

Interesting. I do not see any errors with GCC 8.4 (CentOS 8)

[richardlau]

On CentOS Stream release 8 I do not get errors with either the default GCC 8.4 or GCC 9.2 (via gcc-toolset-9) but do get them with GCC 10.2 (gcc-toolset-10).