isosig-impl.h decodeInts usage in fromIsoSig causes template syntax error

[fogti]

when compiling with

gcc (Gentoo 13.3.1_p20240614 p17) 13.3.1 20240614
Copyright (C) 2023 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

The following error is raised:

In file included from /import/y2data/home/fogti/devel/_read-only/regina/python/generic/triangulation-bindings.h:40,
                 from /import/y2data/home/fogti/devel/_read-only/regina/python/generic/triangulation8.cpp:33:
/import/y2data/home/fogti/devel/_read-only/regina/engine/triangulation/detail/isosig-impl.h: In static member function ‘static regina::Triangulation<dim> regina::detail::TriangulationBase<<anonymous> >::fromIsoSig(const std::string&)’:
/import/y2data/home/fogti/devel/_read-only/regina/engine/triangulation/detail/isosig-impl.h:343:33: warning: expected ‘template’ keyword before dependent template name [-Wmissing-template-keyword]
  343 |             auto joinDest = dec.decodeInts<size_t>(nJoins, nChars);
      |                                 ^~~~~~~~~~
      |                                 template
/import/y2data/home/fogti/devel/_read-only/regina/engine/triangulation/detail/isosig-impl.h:343:50: error: expected primary-expression before ‘>’ token
  343 |             auto joinDest = dec.decodeInts<size_t>(nJoins, nChars);
      |                                                  ^
/import/y2data/home/fogti/devel/_read-only/regina/engine/triangulation/detail/isosig-impl.h:344:35: warning: expected ‘template’ keyword before dependent template name [-Wmissing-template-keyword]
  344 |             auto joinGluing = dec.decodeInts<typename Perm<dim+1>::Index>(
      |                                   ^~~~~~~~~~
      |                                   template
/import/y2data/home/fogti/devel/_read-only/regina/engine/triangulation/detail/isosig-impl.h:344:73: error: expected ‘(’ before ‘>’ token
  344 |             auto joinGluing = dec.decodeInts<typename Perm<dim+1>::Index>(
      |                                                                         ^
      |                                                                         (

At first I thought this was caused by bbb1501, but it doesn't seem so, because reverting it just effectively moves the error to dec.decodeInt instead. Bisect points to dcffc6e being at fault.

[fogti]

Applying the suggestion indeed fixes the error (see also https://stackoverflow.com/questions/77144003/use-of-template-keyword-before-dependent-template-name, https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70417 for context):

diff --git a/engine/triangulation/detail/isosig-impl.h b/engine/triangulation/detail/isosig-impl.h
index 4b99a9c2a..7f50b6ed6 100644
--- a/engine/triangulation/detail/isosig-impl.h
+++ b/engine/triangulation/detail/isosig-impl.h
@@ -340,8 +340,8 @@ Triangulation<dim> TriangulationBase<dim>::fromIsoSig(const std::string& sig) {
                 }
             }
 
-            auto joinDest = dec.decodeInts<size_t>(nJoins, nChars);
-            auto joinGluing = dec.decodeInts<typename Perm<dim+1>::Index>(
+            auto joinDest = dec.template decodeInts<size_t>(nJoins, nChars);
+            auto joinGluing = dec.template decodeInts<typename Perm<dim+1>::Index>(
                 nJoins, IsoSigPrintable<dim>::charsPerPerm);
 
             // End of component!