[brooke2k]

Not sure about GCC, but in general there has been a big move away from using parser generators like flex/bison/ANTLR/etc, and towards using handwritten recursive descent parsers. Clang (which is the C/C++ frontend for LLVM) does this, and so does rustc.

[afdbcreid]

I don't know a single mainstream language that uses parser generators. Python used to, and even they have moved.

AFAIK the reason is solely error messages: the customization available with handwritten parsers is just way better for the user.

[muvlon]

I'll let you decide whether it counts as "mainstream", but the principal implementation of Nix has a very old school setup using bison and flex:

https://github.com/NixOS/nix/blob/master/src/libexpr/parser....

https://github.com/NixOS/nix/blob/master/src/libexpr/lexer.l

[sanxiyn]

Ruby also used to use Bison, uses its own https://github.com/ruby/lrama these days.

[gpderetta]

I believe that GCC also moved to a handwritten parser, at least for c++, a couple of decades ago.