Bug 1711811 Comment 0 Edit History

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Original comment by
on 
Building with GCC 11 fails with:
```
[task 2021-05-19T00:00:35.298Z] 00:00:35     INFO -  In file included from Unified_cpp_accessible_xpcom0.cpp:65:
[task 2021-05-19T00:00:35.299Z] 00:00:35     INFO -  /builds/worker/checkouts/gecko/accessible/xpcom/xpcAccessibleHyperText.cpp: In member function 'virtual nsresult mozilla::a11y::xpcAccessibleHyperText::GetTextAttributes(bool, int32_t, int32_t*, int32_t*, nsIPersistentProperties**)':
[task 2021-05-19T00:00:35.299Z] 00:00:35    ERROR -  /builds/worker/checkouts/gecko/accessible/xpcom/xpcAccessibleHyperText.cpp:194:31: error: 'this' pointer is null [-Werror=nonnull]
[task 2021-05-19T00:00:35.299Z] 00:00:35     INFO -    194 |       props->SetStringProperty(attrs[i].Name(), attrs[i].Value(), unused);
[task 2021-05-19T00:00:35.299Z] 00:00:35     INFO -        |       ~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
[task 2021-05-19T00:00:35.299Z] 00:00:35     INFO -  /builds/worker/checkouts/gecko/accessible/xpcom/xpcAccessibleHyperText.cpp: In member function 'virtual nsresult mozilla::a11y::xpcAccessibleHyperText::GetDefaultTextAttributes(nsIPersistentProperties**)':
[task 2021-05-19T00:00:35.299Z] 00:00:35    ERROR -  /builds/worker/checkouts/gecko/accessible/xpcom/xpcAccessibleHyperText.cpp:223:31: error: 'this' pointer is null [-Werror=nonnull]
[task 2021-05-19T00:00:35.299Z] 00:00:35     INFO -    223 |       props->SetStringProperty(attrs[i].Name(), attrs[i].Value(), unused);
[task 2021-05-19T00:00:35.300Z] 00:00:35     INFO -        |       ~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
[task 2021-05-19T00:00:35.300Z] 00:00:35     INFO -  cc1plus: all warnings being treated as errors
```

The code in both cases, looks like:
```
nsCOMPtr<nsIPersistentProperties> props;
if (...) {
   ...
} else {
   ...
   props->SetStringProperty(...);
}
```

It blows my mind that this obvious null deref hasn't caused crashes on Mac and Linux in the 5 years that this code has been around.
Revision 1 by
on 
Building with GCC 11 fails with:
```
[task 2021-05-19T00:00:35.298Z] 00:00:35     INFO -  In file included from Unified_cpp_accessible_xpcom0.cpp:65:
[task 2021-05-19T00:00:35.299Z] 00:00:35     INFO -  /builds/worker/checkouts/gecko/accessible/xpcom/xpcAccessibleHyperText.cpp: In member function 'virtual nsresult mozilla::a11y::xpcAccessibleHyperText::GetTextAttributes(bool, int32_t, int32_t*, int32_t*, nsIPersistentProperties**)':
[task 2021-05-19T00:00:35.299Z] 00:00:35    ERROR -  /builds/worker/checkouts/gecko/accessible/xpcom/xpcAccessibleHyperText.cpp:194:31: error: 'this' pointer is null [-Werror=nonnull]
[task 2021-05-19T00:00:35.299Z] 00:00:35     INFO -    194 |       props->SetStringProperty(attrs[i].Name(), attrs[i].Value(), unused);
[task 2021-05-19T00:00:35.299Z] 00:00:35     INFO -        |       ~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
[task 2021-05-19T00:00:35.299Z] 00:00:35     INFO -  /builds/worker/checkouts/gecko/accessible/xpcom/xpcAccessibleHyperText.cpp: In member function 'virtual nsresult mozilla::a11y::xpcAccessibleHyperText::GetDefaultTextAttributes(nsIPersistentProperties**)':
[task 2021-05-19T00:00:35.299Z] 00:00:35    ERROR -  /builds/worker/checkouts/gecko/accessible/xpcom/xpcAccessibleHyperText.cpp:223:31: error: 'this' pointer is null [-Werror=nonnull]
[task 2021-05-19T00:00:35.299Z] 00:00:35     INFO -    223 |       props->SetStringProperty(attrs[i].Name(), attrs[i].Value(), unused);
[task 2021-05-19T00:00:35.300Z] 00:00:35     INFO -        |       ~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
[task 2021-05-19T00:00:35.300Z] 00:00:35     INFO -  cc1plus: all warnings being treated as errors
```

The code in both cases, looks like:
```
nsCOMPtr<nsIPersistentProperties> props;
if (...) {
   props = ...
} else {
   ...
   props->SetStringProperty(...);
}
```

It blows my mind that this obvious null deref hasn't caused crashes on Mac and Linux in the 5 years that this code has been around.

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