[pjmlp]

Define modern.

IDEs with such capabilities were already available in the 1990's.

I became an XEmacs user in the 1990's, because there was hardly anything better in UNIX systems.

Remember, Emacs still lacked many niceties only available on XEmacs, and vim was yet to be invented.

This is how old such IDE features have been available.

[bitwize]

XEmacs only came about because Lucid needed a front end to their IDE, Energize, which was extremely comprehensive and could even do "edit and continue" style development of C++ on Unix but, as jwz has it, the Unix community preferred its stone-knives-and-bearskins approach with command line tools.

[pjmlp]

Yeah, Solaris and NeXTSTEP were the only UNIXes that had an IDE tooling story from the vendors.

Thanks to its origin, XEmacs also had for several years many graphical capabilities, that if I am not mistaken only landed on main Emacs during the late 2000's, by then I was back into IDE land.