"And a useful C++ IDE absolutely does have to understand the template system"
I've never seen a C++ IDE that could fully type-check template-heavy library code before its actually used beyond just syntax checking and limited type-checking the non-generic types. This is something that can't be done just because of how C++ templates are specified ("duck-typing"), not due to an implementation detail in the compiler/IDE. This is also the reason why good error-messages from templates are so hard to make - type errors are detected at the concrete level (late), not at the generic level (early). This is going to change when C++ finally gets "concepts" and will be able to reason about generic types (but this would be still a very long way to something like Haskell or Scala has).
I've never seen a C++ IDE that could fully type-check template-heavy library code before its actually used beyond just syntax checking and limited type-checking the non-generic types. This is something that can't be done just because of how C++ templates are specified ("duck-typing"), not due to an implementation detail in the compiler/IDE. This is also the reason why good error-messages from templates are so hard to make - type errors are detected at the concrete level (late), not at the generic level (early). This is going to change when C++ finally gets "concepts" and will be able to reason about generic types (but this would be still a very long way to something like Haskell or Scala has).