[Issue 18698] static foreach + __traits(allMembers, moduleName)

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https://issues.dlang.org/show_bug.cgi?id=18698

Nicholas Wilson  changed:

   What|Removed |Added

 Status|NEW |RESOLVED
 CC||iamthewilsona...@hotmail.co
   ||m
 Resolution|--- |WORKSFORME

--- Comment #18 from Nicholas Wilson  ---
This works now, test case added in https://github.com/dlang/dmd/pull/10016

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[Issue 18698] static foreach + __traits(allMembers, moduleName)

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https://issues.dlang.org/show_bug.cgi?id=18698

Simen Kjaeraas  changed:

   What|Removed |Added

 CC||simen.kja...@gmail.com

--- Comment #17 from Simen Kjaeraas  ---
As a workaround for now, you can use a string mixin:


import std.conv : to;
string create() {
string s = "";
static foreach (i, e; __traits(allMembers, mixin(__MODULE__))) {
s ~= "int n"~i.to!string~";";
}
return s;
}
mixin(create());
pragma(msg, __traits(allMembers, mixin(__MODULE__))); // tuple("object",
"create", "n0", "n1")


The root cause is, as Ketmar pointed out in comment #2, that
__traits(allMembers) tries to expand the static foreach, and the static foreach
calls __traits(allMembers), leading to unbounded mutual recursion and
eventually a stack overflow. The exact same issue occurs if a template mixin in
used in place of the string mixin in the above example.

This makes some sense - how can you iterate over all members when the list
isn't complete yet? For the sake of pragmatism though, it's probably sensible
to allow iteration of the incomplete list, and certainly having the compiler
crash is less than optimal.

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[Issue 18698] static foreach + __traits(allMembers, moduleName)

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https://issues.dlang.org/show_bug.cgi?id=18698

--- Comment #16 from Manu  ---
I remember my work-around; I ran the foreach inside a static module
constructor!
>From there I generated my reflection information about the module and
registered it at runtime (in the module constructor), rather than emit data
directly into the module scope.

In this instance, I really need to emit functions into the module scope, and
not do runtime registration like I did last time.
It would be really really nice to fix this issue!

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[Issue 18698] static foreach + __traits(allMembers, moduleName)

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https://issues.dlang.org/show_bug.cgi?id=18698

--- Comment #15 from Manu  ---
Okay, I must have had some workaround... I don't remember what exactly, it was
some years ago. I probably wrapped it in layers until it worked.
Regardless, it should work. My colleague just tried to do this and asked me why
it didn't work...
I have no recollection of workarounds I might have used.

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[Issue 18698] static foreach + __traits(allMembers, moduleName)

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https://issues.dlang.org/show_bug.cgi?id=18698

Seb  changed:

   What|Removed |Added

 CC||greensunn...@gmail.com

--- Comment #14 from Seb  ---
Here's the regression tester with all 19 versions from 2.060 to 2.079:

https://run.dlang.io/is/ZBosCr

Anyhow, I think we all agree that Manu's use case should work, so let's focus
on fixing that (and avoid the off-topic discussion whether this may or may nor
have worked a long time ago).

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[Issue 18698] static foreach + __traits(allMembers, moduleName)

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https://issues.dlang.org/show_bug.cgi?id=18698

--- Comment #13 from Ketmar Dark  ---
>Think D2.042
easy deal: http://downloads.dlang.org/releases/2010/

[pts/44:ketmar]:D/_old_dmd% ./dmd2/linux/bin/dmd
Digital Mars D Compiler v2.042
Copyright (c) 1999-2010 by Digital Mars written by Walter Bright

[pts/44:ketmar]:D/_old_dmd% ./dmd2/linux/bin/dmd -c test.d
test.d(2): Declaration expected, not 'foreach'
test.d(2): Declaration expected, not '__traits'
test.d(5): unrecognized declaration

exactly the same error with 2.039. should i go even further back in time? or,
fast-forward to 2.059: still the same thing. it. never. worked.

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[Issue 18698] static foreach + __traits(allMembers, moduleName)

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https://issues.dlang.org/show_bug.cgi?id=18698

--- Comment #12 from Manu  ---
I'd love to paste code... But I wrote it in 2012 at a company I don't work at
anymore.
Think D2.042...

I'll see what I can do when I'm not in bed on a phone. But I have no idea what
now I can offer. I used to take function prototypes at top level, and mixin
their bodies at the same scope. My entire system was based on this.

They didn't fly me to dconf to talk about code that didn't compile.

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[Issue 18698] static foreach + __traits(allMembers, moduleName)

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https://issues.dlang.org/show_bug.cgi?id=18698

--- Comment #11 from Ketmar Dark  ---
  module test;
  foreach(m; __traits(allMembers, test))
  {
pragma(msg, m);
  }

rdmd --force --compiler=ldc --eval="pragma(msg, __VERSION__);"
2073L

rdmd --force --compiler=ldc -c test.d
test.d(2): Error: declaration expected, not 'foreach'
test.d(2): Error: declaration expected, not '__traits'
test.d(5): Error: unrecognized declaration

2.073 is *way* before `static foreach`.

so please, code sample and compiler version. if it used to work, and now
doesn't, this is clearly a regression nobody noticed.

the same for old `foreach` code that doesn't work as it used to work before,
please.

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[Issue 18698] static foreach + __traits(allMembers, moduleName)

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https://issues.dlang.org/show_bug.cgi?id=18698

--- Comment #10 from Manu  ---
Remove the 'static' from my OP and you have it.

It definitely worked. They flew me to dconf in 2013 and I gave a whole lecture
about it.
I don't work there anymore, so I don't have the code. I was starting to write a
new version.

Emitting an error instructing me to insert 'static' is at least once change in
old foreach.

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[Issue 18698] static foreach + __traits(allMembers, moduleName)

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https://issues.dlang.org/show_bug.cgi?id=18698

--- Comment #9 from Ketmar Dark  ---
>Non-static foreach doesn't seem to be the same.
example, please. *nothing* was changed in old foreach.

>And it definitely worked at top level.
example, please. i have several different compiler versions at hand, starting
from 2.073 (WAY before static foreach), and top-level foreach doesn't work in
all of them. please, give example code and compiler version where it worked.
thank you.

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[Issue 18698] static foreach + __traits(allMembers, moduleName)

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https://issues.dlang.org/show_bug.cgi?id=18698

--- Comment #8 from Manu  ---
Non-static foreach doesn't seem to be the same. There are new errors with old
usage of foreach instructing to use static foreach instead.

And it definitely worked at top level. I was using it to generate top level
binding stub functions almost as long as I've been using D.

It would be inside a mixin template mixed in at top level, that's all.

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[Issue 18698] static foreach + __traits(allMembers, moduleName)

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https://issues.dlang.org/show_bug.cgi?id=18698

--- Comment #7 from Ketmar Dark  ---
`foreach` never worked at the top level. and non-static forach works *exactly*
the same as before. you are clearly has a very different compiler than the rest
of us.

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[Issue 18698] static foreach + __traits(allMembers, moduleName)

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https://issues.dlang.org/show_bug.cgi?id=18698

--- Comment #6 from Manu  ---
I used 'foreach', which doesn't work anymore.
Since static foreach was added, the non-static one doesn't work the same.
static foreach should to all the static stuff that foreach used to do.

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[Issue 18698] static foreach + __traits(allMembers, moduleName)

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https://issues.dlang.org/show_bug.cgi?id=18698

--- Comment #5 from Ketmar Dark  ---
[i]>I've been using this for almost 10 years[/i]
static foreach? so you really have a time machine, or a specially-crafted
compiler version you never gave others?! please, can you show us the 10 yo code
with `static foreach`, and the 10 yo old compiler you used to compile it?

this is normal thing for new language feature: some cases are missed. it will
eventually be fixed, and in the meantime you can write the code like us, mere
mortals did for those 10 years: without `static foreach`.

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[Issue 18698] static foreach + __traits(allMembers, moduleName)

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https://issues.dlang.org/show_bug.cgi?id=18698

greenify  changed:

   What|Removed |Added

 CC||greeen...@gmail.com

--- Comment #4 from greenify  ---
Static foreach has been added in summer 2017 - how could you have been using
this for ten years?

(if this really is a regression, please describe it better so that everyone
understands it. Otherwise I think ketmar's assessment of this being an
oversight when static foreach was added.

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[Issue 18698] static foreach + __traits(allMembers, moduleName)

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https://issues.dlang.org/show_bug.cgi?id=18698

--- Comment #3 from Manu  ---
I barely understood a word of that post.
Point is, this used to work... I've been using this for almost 10 years to do a
bunch of codegen for stuff in module scope.

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[Issue 18698] static foreach + __traits(allMembers, moduleName)

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https://issues.dlang.org/show_bug.cgi?id=18698

Ketmar Dark  changed:

   What|Removed |Added

 CC||ket...@ketmar.no-ip.org

--- Comment #2 from Ketmar Dark  ---
lol. another `static foreach` great feature: `allMembers` tries to expand
`static foreach`, effectively executing it's body, whith calls `allMembers`,
which tries to expand `static foreach`, effectively...

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[Issue 18698] static foreach + __traits(allMembers, moduleName)

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https://issues.dlang.org/show_bug.cgi?id=18698

--- Comment #1 from Manu  ---
I try this:

  module test;
  alias Members = __traits(allMembers, test);

> Error: basic type expected, not `__traits`

We *really* need to fix that one...

So:

  module test;
  import std.meta;
  alias Members = AliasSeq!(__traits(allMembers, test));
  pragma(msg, Members);

> tuple("object", "std", "arr", "t", "Members")

Okay, that's good.

  static foreach(m; Members)
  {
pragma(msg, m);
  }

Error: template instance AliasSeq!(__traits(allMembers, test)) recursive
template expansion


Oh dear...

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