[C++ Patch] PR 79361

[Paolo Carlini <paolo dot carlini at oracle dot com>]

Hi,

in this error recovery regression, we ICE after (a lot after) a sensible 
diagnostic, when lower_function_body encounters an error_mark_node. I 
worked quite a bit on the issue, and, all in all, I propose to simply 
check the return value of duplicate_decls as called by 
register_specialization and bail out.

In principle it may make sense to continue and, for example, also emit 
diagnostic about '= default' making sense only for special member 
functions - returning spec instead of error_mark_node would achieve that 
without regressions for the second testcase - but I'm not sure we want 
to do this kind of change right here right now together with fixing the 
ICE, because we do *not* emit additional diagnostic in the non-template 
case, eg for:

void foo(int) {}
void foo(int) = default;

Tested x86_64-linux.

Thanks, Paolo.

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Attachment: patch_79361
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