[compiler-rt] Fix broken (flaky) unittests based on FlagParser.

[etienneb]

Summary

The FlagParser is populating a static global class with the
unrecognized flags when parsing. That global class has a
dcheck that limit the number of unrecognized flag to 20.

class UnknownFlags {
  static const int kMaxUnknownFlags = 20;
  const char *unknown_flags_[kMaxUnknownFlags];
  int n_unknown_flags_;

  [...]

  void Report() {
    if (!n_unknown_flags_) return;
    Printf("WARNING: found %d unrecognized flag(s):\n", n_unknown_flags_);
    for (int i = 0; i < n_unknown_flags_; ++i)
      Printf("    %s\n", unknown_flags_[i]);
    n_unknown_flags_ = 0;
  }
};

UnknownFlags unknown_flags;

Unittests based on that class must reset the counter 'n_unknown_flags_' or
the next usage of that class may fail arbitrary. This can be done by
reporting the pending unknown flags.

[rnk]

lgtm This will cause stderr spew in the tests for unknown flags, but that seems OK.

[etienneb]

In D21896#471316, @rnk wrote:

lgtm This will cause stderr spew in the tests for unknown flags, but that seems OK.

Yes. But it's not too noisy.

Note: Google Test filter = SanitizerCommon.*Flags
[==========] Running 6 tests from 1 test case.
[----------] Global test environment set-up.
[----------] 6 tests from SanitizerCommon
[ RUN      ] SanitizerCommon.BooleanFlags
[       OK ] SanitizerCommon.BooleanFlags (0 ms)
[ RUN      ] SanitizerCommon.IntFlags
[       OK ] SanitizerCommon.IntFlags (8 ms)
[ RUN      ] SanitizerCommon.StrFlags
WARNING: found 2 unrecognized flag(s):
    --flag_name
    zzzzzzz
[       OK ] SanitizerCommon.StrFlags (0 ms)
[ RUN      ] SanitizerCommon.MultipleFlags
[       OK ] SanitizerCommon.MultipleFlags (0 ms)
[ RUN      ] SanitizerCommon.CommonSuffixFlags
[       OK ] SanitizerCommon.CommonSuffixFlags (0 ms)
[ RUN      ] SanitizerCommon.CommonFlags
[       OK ] SanitizerCommon.CommonFlags (0 ms)
[----------] 6 tests from SanitizerCommon (8 ms total)

[----------] Global test environment tear-down
[==========] 6 tests from 1 test case ran. (8 ms total)
[  PASSED  ] 6 tests.

lib/sanitizer_common/tests/sanitizer_flags_test.cc

void TestFlag(const char *start_value, const char *env,
   const char *flag = start_value;
 
   FlagParser parser;
   RegisterFlag(&parser, kFlagName, kFlagDesc, &flag);
 
   parser.ParseString(env);
 
   EXPECT_EQ(0, internal_strcmp(final_value, flag));
+
+  // Reporting unrecognized flags is needed to reset them.
+  ReportUnrecognizedFlags();  
 }
 
 TEST(SanitizerCommon, BooleanFlags) {
   TestFlag(false, "flag_name=1", true);
   TestFlag(false, "flag_name=yes", true);
   TestFlag(false, "flag_name=true", true);
   TestFlag(true, "flag_name=0", false);
   TestFlag(true, "flag_name=no", false);
static void TestTwoFlags(const char *env, bool expected_flag1,
   FlagParser parser;
   RegisterFlag(&parser, name1, kFlagDesc, &flag1);
   RegisterFlag(&parser, name2, kFlagDesc, &flag2);
 
   parser.ParseString(env);
 
   EXPECT_EQ(expected_flag1, flag1);
   EXPECT_EQ(0, internal_strcmp(flag2, expected_flag2));
+
+  // Reporting unrecognized flags is needed to reset them.
+  ReportUnrecognizedFlags();    
 }
 
 TEST(SanitizerCommon, MultipleFlags) {
   TestTwoFlags("flag1=1 flag2='zzz'", true, "zzz");
   TestTwoFlags("flag2='qxx' flag1=0", false, "qxx");
   TestTwoFlags("flag1=false:flag2='zzz'", false, "zzz");
   TestTwoFlags("flag2=qxx:flag1=yes", true, "qxx");
   TestTwoFlags("flag2=qxx\nflag1=yes", true, "qxx");