On 7/18/24 12:03 PM, Seyed Sajad Kahani wrote:
When deducing auto for `adc_return_type`, `adc_variable_type`, and
`adc_decomp_type` contexts (at the usage time), we try to resolve the outermost
template arguments to be used for satisfaction. This is done by one of the
following, depending on the scope:
1. Checking the `DECL_TEMPLATE_INFO` of the current function scope and
extracting DECL_TI_ARGS from it for function scope deductions (pt.cc:31236).
2. Checking the `DECL_TEMPLATE_INFO` of the declaration (alongside with other
conditions) for non-function scope variable declaration deductions
(decl.cc:8527).
Then, we do not retrieve the deeper layers of the template arguments; instead,
we fill the missing levels with dummy levels (pt.cc:31260).
The problem (that is shown in PR114915) is that we do not consider the case
where the deduction happens in a template specialization scope. In this case,
the type is not dependent on the outermost template arguments (which are
the specialization arguments). Yet, we still resolve the outermost template
arguments, and then the number of layers in the template arguments exceeds the
number of levels in the type. This causes the missing levels to be negative.
This leads to the rejection of valid code and ICEs (like segfault) in the
release mode. In the debug mode, it is possible to show as an assertion failure
(when creating a tree_vec with a negative size).
This patch resolves PR114915 by replacing the logic that fills in the
missing levels in do_auto_deduction in cp/pt.cc.
The new approach now trims targs if the depth of targs is deeper than desired
(this will only happen in specific contexts), and still fills targs with empty
layers if it has fewer depths than expected.
I would prefer to set outer_targs correctly in the first place, where
it's currently set a few lines above. And to factor that out so other
callers can use it as well instead of DECL_TI_ARGS.
It seems like we want something close to outer_template_args, but it
doesn't currently handle function scope decls or full specializations.
Jason
