src: fix compiler warnings in node_buffer.cc

[danbev]

Currently the following compiler warnings are generated on Linux:

../src/node_buffer.cc:
In function 'void node::Buffer::{anonymous}::StringSlice(
    const v8::FunctionCallbackInfo<v8::Value>&)
      [with node::encoding encoding = (node::encoding)1]':
../src/node_buffer.cc:54:20: warning:
'start' may be used uninitialized in this function
[-Wmaybe-uninitialized]
   if (end < start) end = start;
                    ^~~
../src/node_buffer.cc:50:10: note: 'start' was declared here
   size_t start;
          ^~~~~

This commit initializes start and end to zero to avoid these warnings.

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• commit message follows commit guidelines

[nodejs-github-bot]

@danbev build started: https://ci.nodejs.org/blue/organizations/jenkins/node-test-pull-request-lite-pipeline/detail/node-test-pull-request-lite-pipeline/2357/pipeline

[danbev]

CI: https://ci.nodejs.org/job/node-test-pull-request/20284/

[danbev]

Re-run of failing node-test-commit-arm-fanned :

[mhdawson]

LGTM

[addaleax]

CI: https://ci.nodejs.org/job/node-test-pull-request/20359/

Did you check what path led to these variables potentially being used while initialized? I’d be curious whether this was an actual bug in our code…

[danbev]

Did you check what path led to these variables potentially being used while initialized?

I can't see that these variables would ever be uninitialized, as that initialization happens in ParseArrayIndex and then the return value is guarded by the THROW_AND_RETURN_IF_OOB macro. But I'll take a closer look as I did not do a closer inspection or debugging (I was mainly trying to silence this warning similar to what is done for other compilers like clang which does not generate a warning for these statements).

From looking into this I can't find that there was a bug. The StringSlice function which uses the SLICE_START_END macro is used by asciiSlice, base64Slice, latin1Slice, hexSlice, ucsSlice, and utfSlice. These are all called from lib/buffer.js stringSlice which is only called by Buffer.prototype.toString which checks all the input arguments.

For CompareOffset is called by Buffer.prototype.compare and also checks the input arguments.

[danbev]

Landed in d310d8d.