LLVM has 2.5 million lines of code, but I think it also depends upon the number of templated methods etc, not just LOC.
I'm surprised you haven't seen this point made many times. It would be a full-time job on the internet asking people why they have code completion issues with C++ IDEs.
No, I know what you're talking about; this is an issue in general if you'd not using tooling that's aware of the ins and outs of C++. The point is that the IDEs I have used essentially run the compiler on the file, so they can actually understand what the templates are doing and get through them.
Templates can inherently not be understood. It's duck typing 3 degrees of freedom with 3 unknowns. You need concepts which adds 1 known into the equation, (the final missing degree of freedom is the dreaded ctrl-click-into-an-interface-instead-of-the-concrete-class which is hard to avoid). Tell me one IDE that will give any meaningful information about buzz in the example below:
Other than that, finding foo<T> is usually easy, i've had good experience with qtcreator or clangd, you just have to be very very sure that your include paths are correct, qtcreator is good in that it uses CMakeLists as project-files so all this is done automaticaly.
