What's not mentioned in the announcement (at least based on a quick skim) is that EDG the company is winding down, which is likely the reason why they're open sourcing the front end.
For background -- and I am not an expert here -- their C++ frontend is widely known. I first heard of it because Visual C++'s Intellisense uses it, which was notable because VC does not use the msvc frontend for its own completion. I understand it's been either used or evaluated for other frontends in the past too. I worked as PM for one C++ product, and was fortunate to be able to learn a lot from our engineers; we didn't use it, but they thought highly of EDG.
It has a very strong reputation for being correct. And as such, I think open sourcing it will be a very beneficial thing for the C++ community.
There are essentially four C++ frontends: gcc, clang, MSVC, and EDG. Pretty much every C++ compiler is a reskinned version of one of those compilers. Most of the proprietary compilers have been slinking away from using EDG to using clang (e.g., Intel did this transition a few years ago).
The reason why the EDG frontend is being open-sourced is because EDG itself is closing up shop, and the open sourcing is an interim solution as EDG's customers work on migrating to using Clang instead. So... it's really not good news, because it means that one of the frontends is basically reaching end-of-life.
Ah, I used EDG for static analysis, but joined when we were switching over to using Clang for the frontend. I can't say for sure, but part of it was definitely just to save money using open source. The code that was hacked on top of EDG was also ridiculous, so there was a lot of accumulated tech debt there.
Looking back at that code definitely brings back memories. As a consumer of both frontends, I will say I much preferred working with Clang's. Both needed extra work on top to support everything we needed. Maybe I'm just not as acquainted with C as I would like to be. It's cool to look at this again, though.
It's got history! That's really unusual for moves to open-source; the dates on the earliest commits are in 1990 and they do go forward in time so that's really unusual to have that much history. I bet there's some fun stuff in there.
Despite using C++ for a few years now, the EDG source code is still mostly C code (and in fact, the C++ code is still using the old .c file names). In particular, there's no usage of the C++ standard library.
Where other languages might use inheritance, EDG still uses the C-style `union { ... } variant;`.
On a related note, compiling EDG is extremely fast: on my machine, the EDG frontend compiles in <10s; whereas clang takes >10min (caution unfair comparison: clang includes much more than just a frontend).
I think this is fairly common practice when writing compilers. You ideally want to be able to bootstrap from other languages, and C is a much simpler starting point.
Yes, of course. It makes complete sense to have the implementation of a C++ compiler to be written in a highly portable and much simpler language like C.
If I remember correctly, EDG was the only C++ implementation that actually attempted to implement the export keyword for templates in old C++. It was this implementation experience that informed the deprecation of export. EDG is a major influence in the development of C++.
Ooh, fond (and some not so fond) memories of when Silicon Graphics' (MIPS) C and C++ compilers were based on EDG's frontend, with a custom ucode-generating backend, and integrated into CASEVision. Early 1990s.
It has an interesting code style, the comments go _after_ the function definition but before the opening bracket.
It looks weird, but it actually makes sense! The flow is more natural - first the function definition, and then the explanation of what it does. It also avoids repeating the function name.
I write comments about what a function does and it's interface before, but comments about the implementation after. Also my pre- and post-conditions go there of course. (I'm mostly writing in C.)
It's one of the 4 big remaining C++ compiler frontends: gcc, clang, MSVC, EDG.
Most other C++ compilers are based on either EDG or clang. (e.g. the Intel C++ compiler used to be based on the EDG frontend, though modern versions are based on clang instead)
The "frontend" is the part of the compiler that understands the input language: lexer, parser, template instantiation, constexpr evaluation, ...
The EDG frontend produces an intermediate representation (IL) that is then used by the different compiler vendors to generate machine code. Or do code analysis.
TLDR EDG C++ is a compiler frontend developed by EDG since the 80s which has been used under the hood for a whole bunch of commercial C and C++ compilers, static analyzers, linters, and IDE code completion tools.
Odds are if you are familiar with a closed source tool in one of those categories above, there's a decent chance it uses EDG's frontend somewhere in it under the hood.
https://en.wikipedia.org/wiki/Edison_Design_Group ref 9: https://herbsutter.com/2025/11/10/trip-report-november-2025-...
For background -- and I am not an expert here -- their C++ frontend is widely known. I first heard of it because Visual C++'s Intellisense uses it, which was notable because VC does not use the msvc frontend for its own completion. I understand it's been either used or evaluated for other frontends in the past too. I worked as PM for one C++ product, and was fortunate to be able to learn a lot from our engineers; we didn't use it, but they thought highly of EDG.
It has a very strong reputation for being correct. And as such, I think open sourcing it will be a very beneficial thing for the C++ community.
The reason why the EDG frontend is being open-sourced is because EDG itself is closing up shop, and the open sourcing is an interim solution as EDG's customers work on migrating to using Clang instead. So... it's really not good news, because it means that one of the frontends is basically reaching end-of-life.
But also quite sad. They've announced that they are closing down.
The source code itself: https://github.com/edgcpp/compiler
Documentation: https://edgcpp.org/doc/
And for those curious the license SPDX is: Apache-2.0 WITH LLVM-exception
i.e.
- https://spdx.org/licenses/Apache-2.0.html
- https://spdx.org/licenses/LLVM-exception.html
Looking back at that code definitely brings back memories. As a consumer of both frontends, I will say I much preferred working with Clang's. Both needed extra work on top to support everything we needed. Maybe I'm just not as acquainted with C as I would like to be. It's cool to look at this again, though.
EDIT: But in this case it seems something significant is being released, it would be better with less writing and more human if possible.
Where other languages might use inheritance, EDG still uses the C-style `union { ... } variant;`.
On a related note, compiling EDG is extremely fast: on my machine, the EDG frontend compiles in <10s; whereas clang takes >10min (caution unfair comparison: clang includes much more than just a frontend).
One of EDG developers prototyped his idea, and brought it to WG21 when it seemed reflection as originally thought for C++17 was never happening.
EDG was just 3 guys back then.
It looks weird, but it actually makes sense! The flow is more natural - first the function definition, and then the explanation of what it does. It also avoids repeating the function name.
void func(var1, var2) int var1, char* var2. { ... }
perhaps some legacy from that? Probably not, but just first thing that popped into my head since it feels similar :shrug:
The "frontend" is the part of the compiler that understands the input language: lexer, parser, template instantiation, constexpr evaluation, ... The EDG frontend produces an intermediate representation (IL) that is then used by the different compiler vendors to generate machine code. Or do code analysis.
EDG can also be used as a C++-to-C compiler.
Nice to see this still exists!
After all, this is how it all started back in the days of - what was it called again ? - yeah, cfront
https://en.wikipedia.org/wiki/Cfront
TLDR EDG C++ is a compiler frontend developed by EDG since the 80s which has been used under the hood for a whole bunch of commercial C and C++ compilers, static analyzers, linters, and IDE code completion tools.
Odds are if you are familiar with a closed source tool in one of those categories above, there's a decent chance it uses EDG's frontend somewhere in it under the hood.