> no IDE or tool I've seen does this better.

Modula-2 does it better. Each module split in two files - definition and implementation. Unlike C++ header files, def files are compiled rather that inlined, so they don't have a potential to produce different result for each source file that references them. The result is 100% reliable dependency graph across all source files, no need for a makefile, and blazingly fast compilation (each def file is only parsed and compiled once).