[tialaramex]

> BTW, how many LOC does Crater run in a full test, and how long does it take/how expensive is a run? I failed to find that information.

I have nothing more than a finger in the air estimate for LOC, maybe hundreds of millions?

I have never watched a "full test" like for a release build, I believe those take several days - but when Crater is asked just to build everything that takes a little under 24 hours with its current footprint.

> I strongly suspect VC++ changes/extensions are tested against in-house Microsoft code bases before making their way to the standard, because it makes no sense to undermine your own systems.

Surely it stands to reason that if Microsoft are proposing standardisation of a feature they've shipped in MSVC, that's also a feature they've tried using? This model of ISO C++ features (which the developer of Circle also prefers) maps much better to what was initially envisioned than today's reality however. Most C++ proposals today are not submissions of existing compiler features from the big three compilers (MSVC, GCC and Clang) but instead fresh before the committee, often with no implementation experience at all.

That's certainly one way to do it, after all Rust contributors don't have their own Rust compiler either, but it means you need very different tooling.

1) Breadth matters much more than depth for finding surprises which is the thing you won't get with an ad hoc approach. Going from 10% of some big corporate code base to 20% won't make anywhere near the difference you get from adding a hundred one-man-band projects that are smaller even in total, because different stylistic and idiomatic choices make so much more practical difference for this work.

2) As a result "a few dozen" won't cut it. Try all the C++ on github, that seems like a much better place to start.

3) Sure, the primary goal of WG21 proposers is to get into the IS - it would be nice if what they've proposed actually works, but ultimately if it doesn't work that can be fixed later, whereas if it's not adopted then it doesn't matter whether it would work.

Arguably there have never been any versions of the C++ IS which actually describe a complete working programming language, so it's not terribly important that if it were such a system it would be correct, still there's a preference for fewer rather than more horrible gotchas.

I mentioned #embed so that's a useful example here, C++ 23 doesn't standardize #embed. So in theory C++ code can't use #embed, that's not C++. But of course in reality the vendors are going to ship a pre-processor which handles #embed, they don't care, so it'll work and it's widely expected you will be able to use it even in older C++ verisons.

4) If there was a specification then a tool like Crater might be somewhat helpful for that, but I expect that most effort would remain focused on a single implementation, today that is of course the Rustc compiler with its LLVM backend.

The hypothetical EESmith Rust sounds spurious to me, how could it deliver 2x run-time performance by removing "rarely used features" ? I don't think spurious hypotheticals are a good use of anybody's time.

[eesmith]

> I have nothing more than a finger in the air estimate for LOC, maybe hundreds of millions?

And if there were a number, it would reflect only one of several ways to quantify "LOC", right? Resulting in a spread of numbers that could meaningfully be described as "LOC"?

> Breadth matters much more than depth for finding surprises which is the thing you won't get with an ad hoc approach

I would be quite interested in someone doing a research publication on this topic!

Give the history of using crater, which packages have proved most useful? Do the same core packages prove useful over time, or does the most significant subset change wildly? What does the cumulative distribution plot (#packages until time of appropriate feedback) look like?

How worthwhile is the additional breadth from crates.io + GitHub vs. just crates.io? Is it worthwhile to also include GitLab, and what are the tradeoffs (eg, additional compute costs, additional false positives).

For that matter, how useful would it be to add Linux+ARM to the current Crater tests? Or Microsoft Windows? If breadth is that important, then why skip out on the full set of Rust code you have available?

> As a result "a few dozen" won't cut it.

I did follow up with "If not, would ~100 packages be enough? What about ~1,000?" :)

If there's no equivalent of a dose-response curve / ROC curve / price-performance curve, and the answer is "must try everything" then how do I know the extra effort is useful, rather than FOMO-driven anxiety?

> Try all the C++ on github

Assuming there was a single way to build all C++ code - how much do you think it would cost to compile all the C++ code on GitHub? And why do you think it the additional cost would be worthwhile to C++ standards development?

> but I expect that most effort would remain focused on a single implementation,

Oh, given my experience with Python implementations, I agree!

But my point is processes change when you have multiple competing commercial vendors, which C++ has. So looking at how Rust does things doesn't mean it's also appropriate for C++.

> I don't think spurious hypotheticals are a good use of anybody's time.

Okay, something more practical. C++11 broke backwards compatibility by changing how 'auto' works. "auto int i;" used to be valid, now it's an error. This is a huge boon for usability. It's a trivial syntactic change to fix old code, and long experience shows the old "auto" storage class was rarely used.

How would the systematic compilation of all C++ code on GitHub (assuming that were possible) affect that decision more than the ad hoc methods they did use to make that decision?

Will there really never be something in Rust were a simple breaking change of a rarely used feature can result in an easier-to-use language?

If there can, then you may have a schism, either temporary (gcc vs egcs fork) or more permanent (Perl5/Perl6/Raku). Which will be "Rust"?

The answer is legally quite clear. The Rust Foundation has the trademark to "Rust" (serial number 87796977). My version can't break backwards compatibility, even as a fork, so would have to call it, perhaps, "Verdigris". (As I recall, someone started to develop a "Python 2.8" with more backports from Python 3; the PSF got after them for using the Python trademark that way.)

C++ doesn't have trademark protection, so the legal concept of what is/is not C++ are also different than Rust.

[tialaramex]

> How would the systematic compilation of all C++ code on GitHub (assuming that were possible) affect that decision more than the ad hoc methods they did use to make that decision?

I doubt it would affect the actual decision at all, WG21 has been very comfortable relying on gut instinct, even in the face of reality, so there's no reason they'd be affected by the results of more systematic testing.

> Will there really never be something in Rust were a simple breaking change of a rarely used feature can result in an easier-to-use language?

Now we're talking about something woollier than your performance hypothetical. Surely almost any change can be sold as "easier-to-use" if you're motivated. Herb Sutter seems motivated for example, every CppCon he has a proposal for how to make C++ "easier to use" by further complicating it. An immediate caution though is, in what way is it "easier-to-use" half of a fractured ecosystem ? The other half is no longer available to you, that's certainly not easier to use than before.

Rust programmers aren't used to taking such deals because Editions have been leveraged to give them better alternatives without the compromise.

This promise got stronger over time, rather than weaker as you seem to expect. There's complicated Rust 1.0 era code (e.g. early ripgrep) which doesn't even build today on a current compiler, because something it did is wrong and Rust 1.0 compiler didn't spot that but modern ones do - back then it was less likely they'd see the compatibility break as a big deal, it was "just" a bug fix.

C++ compilers fix those sort of bugs all the time even today. Rust wouldn't take those fixes so easily, modulo crater measurements, but as you've shown C++ doesn't have that.

[eesmith]

> so there's no reason they'd be affected by the results of more systematic testing.

Let's go back to the g'parent comment that started this branch, at https://news.ycombinator.com/item?id=36387994 .

muxator wrote "the author of this little proposal (officializing "_" as a no name placeholder) had to perform a thorough research to show that this change would not break existing code".

What was that "thorough research"? The paper doesn't mention it, but does imply there was a code search to find the examples it listed.

I assume you think that research was also "gut instinct", rather than "thorough research". Is that only because it did not do full compilation of all C++ code on GitHub, or is there something more seriously wrong with that research?

Further, while you wrote "Most C++ proposals today are not submissions of existing compiler features from the big three compilers (MSVC, GCC and Clang) but instead fresh before the committee, often with no implementation experience at all", that specific spec says it was implemented in Clang.

It therefore seems like the proposal which kicked off this long thread is a counter-example to your characterization of C++ language development.

You have not addressed my question - how do you know the extra effort in a full Crater run of all crates in crates.io + GitHub is useful, rather than primarily FOMO-driven anxiety?

[tialaramex]

> I assume you think that research was also "gut instinct", rather than "thorough research".

My goodness no. "Gut instinct" is how the decisions are made, but the research you're talking about was made for a proposal paper. There are different incentives in play.

For the proposer the incentive is to get something to show for the enormous effort expended in making a proposal - usually months, sometimes years, across dozens of meetings and discussions and presentations. It's soul-destroying stuff. Ideally the sub-committees you're seeing would approve your work and it can go to another committee, more likely they will have suggestions for how it could be altered so as to satisfy them, and after a few iterations that can result in approval of a subsequent revised document, often they just have open-ended questions for you, which perhaps might be satisified in some future proposal document, by answering the questions somehow, or they just aren't interested and you're told to go away.

A show of your extensive research might make it easier to achieve your goal. You have an incentive to make this research seem as comprehensive as possible for that purpose in support of your goal.

But the people making the decision don't have that incentive. They could - in principle - spend hours on reading all the work you did, they could - in principle - replicate that work or even do their own research. In reality they are probably thinking about whether they can break early or move on to something they care about more. I would summarise their reasoning as gut instinct. Does this sound like something we should do? Maybe not. Straw poll question: Do we want this? Vote Against, nothing personal.

I mentioned JeanHyde before. JeanHydge has seen how this sausage is made, be sure to read his experience and think about it carefully before believing any fairy tales you've heard or any imagined process. Remember, the essence of JeanHyde's proposal was just this: 1) It would sure be nice to use blobs of binary data in my programs. 2) The existing ways to achieve this are garbage - so we need a new one.

JeanHyde spent years defending basic obvious stuff in front of people strongly motivated to believe he's wrong since that's just easier than doing any work. At its most basic the question, is, given a lot of bytes of data in a file, or a lot of ASCII hexadecimal values written as C literals, which can be processed more quickly ? The committee was strongly motivated to insist the answer was the ASCII hex, even though JeanHyde had tables showing the raw data is much faster.

The committee hallucinated into existence rules like JeanHyde's proposal can't be in the standard unless there are working implementations. If you're wondering why your C++ compiler didn't have a complete C++ 20 implementation in 2021 you might be surprised to hear that there is such a rule -- that's because there is no such rule, it's an excuse.

Another hallucinated rule is very amusing to Rust programmers. WG21 would like to believe that C++ compilation doesn't result in executing code. So, if Bob makes a malicious C++ program, sure, running the program might be bad, but certainly compiling it is fine. This belief is laughable, but laughing at them won't get your proposal accepted, so you must try to navigate the fantasy world they live in, where their C++, which doesn't have this capability, can accept your proposal, without introducing the capability C++ already has. It's like you're playing Mornington Crescent with opponents who believe there are rules and they know what they are. Terrifying.

And so it isn't in C++ 23. The C++ 23 standard doesn't have JeanHyde's proposal. WG14 took #embed for C23, so C23 does have it, and of course in reality C++ programmers can expect to benefit from that, and that's the awful, miserable reality you're defending.

> how do you know the extra effort in a full Crater run of all crates in crates.io + GitHub is useful, rather than primarily FOMO-driven anxiety?

It periodically finds problems. And Rust is equipped to deal with those problems so the forewarning is practically useful.

In C++ if a syntax change breaks some fraction of programs well, too bad. I guess it would be nice to know, but as you saw the committee might (or might not) do it anyway. In Rust, that can be handled via the Editions mechanism. But to do that you need to know about it before you ship the compiler with the syntax change, so as to mark it as applying only to the future edition you're adding it to.