lib/cf-h1-proxy.c: `-Wnull-dereference` warnings with gcc 12 / curl 8.7.1

[vszakats]

I did this

Built curl-for-win with gcc + mingw-w64.
Got these warnings:

.../curl/lib/cf-h1-proxy.c:1060:17: warning: null pointer dereference [-Wnull-dereference]
 1060 |   cf->connected = FALSE;
      |                 ^
.../curl/lib/cf-h1-proxy.c:1061:8: warning: null pointer dereference [-Wnull-dereference]
 1061 |   if(cf->ctx) {
      |      ~~^~~~~
In function 'tunnel_free',
    inlined from 'cf_h1_proxy_destroy' at .../curl/lib/cf-h1-proxy.c:1053:3:
.../curl/lib/cf-h1-proxy.c:198:27: warning: null pointer dereference [-Wnull-dereference]
  198 |   struct h1_tunnel_state *ts = cf->ctx;
      |                           ^~

Ref: https://github.com/curl/curl-for-win/actions/runs/8492022102/job/23264582018#step:3:10749

I expected the following

No warnings.

curl/libcurl version

curl 8.7.1

operating system

Windows (seems OS-agnostic)

[bagder]

Grr, this the overcomplaining errors from gcc's static analyzer coming. Quite annoying.

This happens because in:

  CURL_TRC_CF(data, cf, "close");
  cf->connected = FALSE;

... the macro on the first line checks if cf is non-NULL, which then gcc takes as a confirmation it should complain on line two which uses cf without a NULL check.

I find this warning annoying and counter-productive. The macro is fine to use protection because it can be used in places where maybe it can be a NULL pointer passed to it. It does mean that a NULL pointer is accepted in every place the macro is used.

[vszakats]

I guess a few false positives is the price to pay for detecting real issues.
Also an extra NULL check here in there is probably better than missing
one by accident. But yeah, this is annoying.

The other thing I wondered why this wasn't caught in CI. E.g. in this job (mingw, gcc13, unity): https://ci.appveyor.com/project/curlorg/curl/builds/49500338/job/opyx2nhk46vop8b3?fullLog=true

Then noticed that the affected gcc version was actually 12.2.0, not 13.2.0.
So this may have been fixed, unless I'm missing some other difference.

[vszakats]

This remains valid, but I don't want to offend anybody with warnings popping up in tests.