[PATCH] make excessive template instantiation depth a fatal error

[Manuel López-Ibáñez <lopezibanez at gmail dot com>]

Following a suggestion in PR16564, this patch makes excessive template
instantiation depth a fatal error. In fact, this allows simplifying
the code a lot, just by printing first the context (like we do for
every other diagnostic) instead of printing it after (which is not
possible for a fatal error).

This changes the output of quite a few testcases, so before modifying
those I would like to know whether the idea is OK.

Examples of changed output are:

[Before]
g++.dg/cpp0x/decltype26.C:6:15: error: template instantiation depth
exceeds maximum of 900 (use -ftemplate-depth= to increase the maximum)
substituting 'template<class T> decltype (f(T())) f(T) [with T =
<missing>]'
g++.dg/cpp0x/decltype26.C:6:15:   recursively required by substitution
of 'template<class T> decltype (f(T())) f(T) [with T = A]'
g++.dg/cpp0x/decltype26.C:6:15:   required by substitution of
'template<class T> decltype (f(T())) f(T) [with T = A]'
g++.dg/cpp0x/decltype26.C:13:8:   required from here

g++.dg/cpp0x/decltype26.C: In function 'int main()':
g++.dg/cpp0x/decltype26.C:13:8: error: no matching function for call to 'f(A)'
g++.dg/cpp0x/decltype26.C:6:18: note: candidate: template<class T>
decltype (f(T())) f(T)
g++.dg/cpp0x/decltype26.C:6:18: note:   substitution of deduced
template arguments resulted in errors seen above

[After]

g++.dg/cpp0x/decltype26.C: In substitution of 'template<class T>
decltype (f(T())) f(T) [with T = A]':
g++.dg/cpp0x/decltype26.C:6:15:   recursively required by substitution
of 'template<class T> decltype (f(T())) f(T) [with T = A]'
g++.dg/cpp0x/decltype26.C:6:15:   required by substitution of
'template<class T> decltype (f(T())) f(T) [with T = A]'
g++.dg/cpp0x/decltype26.C:13:8:   required from here
g++.dg/cpp0x/decltype26.C:6:15: fatal error: template instantiation
depth exceeds maximum of 900 (use -ftemplate-depth= to increase the
maximum)


One interesting case is for operator->(). Here we have to adjust
the location of the template instantiations so we can point the
user to the point of recursion:

[Before]

g++.dg/template/arrow1.C:12:11: error: template instantiation depth
exceeds maximum of 900 (use -ftemplate-depth= to increase the maximum)
instantiating 'a<(n + 1)> a<n>::operator->() [with int n = 900]'
g++.dg/template/arrow1.C:12:11:   recursively required from 'a<(n +
1)> a<n>::operator->() [with int n = 0]'
g++.dg/template/arrow1.C:12:11:   required from here

g++.dg/template/arrow1.C:12:11: error: template instantiation depth
exceeds maximum of 900 (use -ftemplate-depth= to increase the maximum)
instantiating 'struct a<901>'
g++.dg/template/arrow1.C:12:11:   recursively required from 'a<(n +
1)> a<n>::operator->() [with int n = 0]'
g++.dg/template/arrow1.C:12:11:   required from here

g++.dg/template/arrow1.C:12:11: error: invalid use of incomplete type
'struct a<901>'
g++.dg/template/arrow1.C:5:8: note: declaration of 'struct a<901>'

[After]

g++.dg/template/arrow1.C: In instantiation of 'a<(n + 1)>
a<n>::operator->() [with int n = 899]':
g++.dg/template/arrow1.C:7:2:   recursively required from 'a<(n + 1)>
a<n>::operator->() [with int n = 1]'
g++.dg/template/arrow1.C:7:2:   required from 'a<(n + 1)>
a<n>::operator->() [with int n = 0]'
g++.dg/template/arrow1.C:12:11:   required from here
g++.dg/template/arrow1.C:12:11: fatal error: template instantiation
depth exceeds maximum of 900 (use -ftemplate-depth= to increase the
maximum)

The rest of testcases follow the pattern:

[Before]

g++.dg/template/pr23510.C:9:1: error: expected ';' after struct definition
g++.dg/template/pr23510.C:6:27: error: template instantiation depth
exceeds maximum of 15 (use -ftemplate-depth= to increase the maximum)
instantiating 'struct Factorial<5u>'
g++.dg/template/pr23510.C:6:27:   recursively required from 'struct
Factorial<19u>'
g++.dg/template/pr23510.C:6:27:   required from 'struct Factorial<20u>'
g++.dg/template/pr23510.C:21:20:   required from here

[After]

g++.dg/template/pr23510.C:9:1: error: expected ';' after struct definition
g++.dg/template/pr23510.C: In instantiation of 'struct Factorial<6u>':
g++.dg/template/pr23510.C:6:27:   recursively required from 'struct
Factorial<19u>'
g++.dg/template/pr23510.C:6:27:   required from 'struct Factorial<20u>'
g++.dg/template/pr23510.C:21:20:   required from here
g++.dg/template/pr23510.C:6:27: fatal error: template instantiation
depth exceeds maximum of 15 (use -ftemplate-depth= to increase the
maximum)

Apart from these changes, the patch bootstraps and passes the
regression suite on x86_64-linux.

OK with the updated testcases?

gcc/cp/ChangeLog:

2014-08-17  Manuel López-Ibáñez  <manu@gcc.gnu.org>

    * error.c (print_instantiation_context): Delete.
    * typeck2.c (build_x_arrow): Record location when pushing
    template instantiation.
    * pt.c (push_tinst_level): Make it a wrapper around ...
    (push_tinst_level_loc): ... this. New function. Make excessive
    template instantiation depth a fatal error. Record location. Use
    bool as return type.
    (instantiate_pending_templates): Make excessive
    template instantiation depth a fatal error.
    (problematic_instantiation_changed): Use bool as return type.
    * cp-tree.h (print_instantiation_context): Delete.
    (push_tinst_level): Update declaration.
    (problematic_instantiation_changed): Likewise.
    (push_tinst_level_loc): New.

gcc/testsuite/ChangeLog:

2014-08-17  Manuel López-Ibáñez  <manu@gcc.gnu.org>

    * lib/gcc.exp: Accept "fatal error:" as error prefix.
    * lib/g++.exp: Likewise.
    * lib/obj-c++.exp: Likewise.
    * lib/objc.exp: Likewise.
    * g++.dg/template/pr16564.C: New test.

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