[C++ Patch] PR 60383

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

Hi,

this 4.9 regression is again an ICE during error recovery: 
check_specialization_namespace errors out, 
maybe_process_partial_specialization doesn't check its return value, and 
the ICE happens much later, in retrieve_specialization, in the gcc_assert:

  /* There should be as many levels of arguments as there are
     levels of parameters.  */
  gcc_assert (TMPL_ARGS_DEPTH (args)
          == (TREE_CODE (tmpl) == TEMPLATE_DECL
          ? TMPL_PARMS_DEPTH (DECL_TEMPLATE_PARMS (tmpl))
          : template_class_depth (DECL_CONTEXT (tmpl))));

Simply checking the return value of check_specialization_namespace and 
early returning error_mark_node appears to work well, with the minor 
complication that check_specialization_namespace may return false also 
in case of permerror, thus the !at_namespace_scope_p. Other than that, 
the tweak to crash95.C doesn't seem bad to me (for example, it aligns 
our diagnostic to that of current clang)

Tested x86_64-linux.

Thanks,
Paolo.

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Attachment: CL_60383
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Attachment: patch_60383
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