http://d.puremagic.com/issues/show_bug.cgi?id=9289

           Summary: [Regression 2.061] Had been deprecated language
                    features are enabled again in default
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: regression
          Priority: P2
         Component: DMD
        AssignedTo: nobody@puremagic.com
        ReportedBy: k.hara.pg@gmail.com


--- Comment #0 from Kenji Hara <k.hara.pg@gmail.com> 2013-01-09 21:32:29 PST ---
This regression is introduced by the "Make deprecations as warnings the
default.
From my comment:
https://github.com/D-Programming-Language/dmd/pull/1287#issuecomment-12080557

---

I found a big breaking introduced by this, in 2.061.

In current, all deprecated language features until 2.060 are accepted in default. For example:

void main() {
    typedef int X = 10;   // !!
    X x;
    assert(x == 10);
}
typedef was deprecated from 2.058, then we couldn't compile the code in
default.
But, from 2.061, we can compile the code and run in default again.

More than worse, all deprecations which reported in semantic phase or later will break code meaning silently.

import std.stdio;
void main() {
    int[] arr;
    static if (is(typeof({ auto ptr = *arr; })))
        writeln("*arr is not deprecated");
    else
        writeln("*arr is deprecated, instead use arr.ptr");
}
The meaning of is(typeof({ auto ptr = *arr; })) is changed in default.

Therefore this is a huge breaking against the language improvement process in the past few years.

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Leandro Lucarella <leandro.lucarella@sociomantic.com> changed:

           What    |Removed                     |Added
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                   |                            |ic.com


--- Comment #1 from Leandro Lucarella <leandro.lucarella@sociomantic.com> 2013-01-10 02:19:27 PST ---
(In reply to comment #0)
> This regression is introduced by the "Make deprecations as warnings the
> default.
> From my comment:
> https://github.com/D-Programming-Language/dmd/pull/1287#issuecomment-12080557
[...]
> Therefore this is a huge breaking against the language improvement process in the past few years.

How the default deprecation handling is changed compared to using -d in 2.060? I'm not entirely convinced is really a regression if is the same.

I understand there is a problem, but I wonder if your suggested solution is really needed:

> To fix the problem, we need to split deprecated language features into the two.
>
>    Truly deprecated features
>    This group contains all language features which already deprecated in 2.060 and earlier.
>        Each of them prints deprecated message without -d switch.
>        Each of them raises an error without -d switch. (Important!!)
>
>    Softly deprecated features
>    This group will print deprecation message for the using but not make an error in default, and may contain newly deprecated features from 2.061.
>        Each of them prints deprecated message without -d switch.
>        Each of them raises an error without -de switch. (Important!!)

Shouldn't be just plain errors the things that you don't want to allow them at all? Or are you suggesting just a migration path to the new way of presenting deprecations?

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Kenji Hara <k.hara.pg@gmail.com> changed:

           What    |Removed                     |Added
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           Keywords|                            |pull


--- Comment #2 from Kenji Hara <k.hara.pg@gmail.com> 2013-01-10 02:32:35 PST ---
(In reply to comment #1)
I brushed up my idea: The -dw/-de switches affect to the use of deprecated
"symbols", but doesn't to the use of deprecated language features.

You can see my implementation. https://github.com/D-Programming-Language/dmd/pull/1459

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Jonathan M Davis <jmdavisProg@gmx.com> changed:

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--- Comment #3 from Jonathan M Davis <jmdavisProg@gmx.com> 2013-01-10 02:37:57 PST ---
> I brushed up my idea: The -dw/-de switches affect to the use of deprecated "symbols", but doesn't to the use of deprecated language features.

That's probably the right way to handle it. Deprecated language features already effectively have the separation between soft and hard deprecation, because they generally get normal warnings before being deprecated, whereas deprecated symbols aren't part of that, since they aren't hard-coded into the compiler.

We can just go back to treating deprecated language features the way that we have and take advantage of the recent changes to deprecated for deprecated symbols.

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--- Comment #4 from Leandro Lucarella <leandro.lucarella@sociomantic.com> 2013-01-10 06:56:59 PST ---
I still don't understand why is it a good idea to treat deprecated language features differently from deprecated symbols. Deprecated language features get a warning but you only get a warning if you use -w, which implies having warnings for lots of other stuff that have nothing to do with deprecations.

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--- Comment #5 from Leandro Lucarella <leandro.lucarella@sociomantic.com> 2013-01-10 07:03:04 PST ---
Well I see the second example from Kenji doesn't print any warnings, that's certainly a problem. But the first example works just fine, it compiles issuing a warning. That is what it's supposed to do, that was the original idea. Is not a bug, is a feature :)

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David Nadlinger <code@klickverbot.at> changed:

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--- Comment #6 from David Nadlinger <code@klickverbot.at> 2013-01-11 16:09:52 PST ---
I'm not sold on the idea of adding additional complexity to the behavior of the deprecation-related switches.

If you feel that some language features should be more than just deprecated by now, why don't chose the obvious option of just turning them into an error?

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Walter Bright <bugzilla@digitalmars.com> changed:

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--- Comment #7 from Walter Bright <bugzilla@digitalmars.com> 2013-01-11 17:30:22 PST ---
(In reply to comment #6)
> I'm not sold on the idea of adding additional complexity to the behavior of the deprecation-related switches.
> 
> If you feel that some language features should be more than just deprecated by now, why don't chose the obvious option of just turning them into an error?

I agree, I think we are overengineering this.

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--- Comment #8 from Jonathan M Davis <jmdavisProg@gmx.com> 2013-01-11 19:12:02 PST ---
Honestly, I think that it would be great in general to be able to distinguish between soft deprecation (warn about it) and hard deprecation (make it an error), but I can also understand not wanting to add that sort of complication to the feature, especially since it's a feature that should be needed relatively rarely. And if you only get one of the two, soft deprecations are far less disruptive, and I think that we were right to make deprecated warn by default, but it does pose a bit of a problem for the language features.

For that, I think that there are two basic approaches which make sense:

1. Make deprecated work as it has been for language features and use normal warnings when we want to "soft" deprecate a language feature, which is exactly what we have been doing. But we keep the new behavior (warn by default) for the deprecated keyword.

2. Make at least some of the currently deprecated language features into errors rather than have them be deprecated. Then have deprecation for language features be exactly the same as it is for the deprecated keyword, so some features end up being errors which can't be disabled, and some become warnings rather than errors by default. If we go that route, we should probably also think about making some of the current warnings into deprecation warnings (e.g. when skipping the use of override).

The second approach would probably be the cleaner of the two, but it does mean that we lose the ability to give an error for language deprecation by default and still allow for the feature to be used. On the other hand, using deprecation warnings instead of normal warnings for deprecating features would be great, because then people don't have to use -w or -wi to see them. And that would make doing stuff like deprecating delete much smoother, since it would ensure that anyone using it got bugged about it rather than just those folks who compile with warnings enabled. It also keeps its behavior in line with the deprecated keyword, which would probably be a good idea if we can reasonably do so.

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--- Comment #9 from Leandro Lucarella <leandro.lucarella@sociomantic.com> 2013-01-21 03:32:36 PST ---
I don't see why language features should be treated differently. The only problem I see right now is deprecated features are not being warn when gagging (I think that's the term for when errors are silent to evaluate something at compile time that is OK to fail, like tratis(compile) or static if's). I think usage of deprecated features there should trigger a warning too. If the idea behind some of this construct is just to test if an old feature is still working, maybe that should be fixed and "calculated" through the compiler's version or something like that.

If we keep deprecated language features as errors by default, we will end up with the exact same problem we had before making deprecations as warnings the default. Why would we want to do that?

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