Beta 2.095.0

[Mathias LANG]

On Thursday, 24 December 2020 at 11:38:11 UTC, Paolo Invernizzi 
wrote:
>
> The point is that the deprecation is coming from an external 
> library, it would be great to have the precise instantiation 
> point in that source code, so I was wondering if that dmd 
> improvement [1] should print a more detailed trace.
>
> [1] https://dlang.org/changelog/2.095.0.html#deprecation-context

It does print a detailed stack trace (up to the first symbol that 
is not a template) if you don't use `-de`. If you use `-de`, 
since the checks in Phobos are `is(typeof(n.toString()))` or 
`__traits(compiles, n.toString())`, then it just changes whether 
or not the code compiles, and as a result changes the output of 
the program. A trivial example:

```
import std.stdio, std.typecons;
struct Foo {
     deprecated string toString() const { return "Oops"; }
}
void main () { writefln("%s", Foo.init); }
```

Will print, with v2.094.2 or before (dmd -run):
```
/usr/local/opt/dmd/include/dlang/dmd/std/format.d(3921): 
Deprecation: function foo.Foo.toString is deprecated
/usr/local/opt/dmd/include/dlang/dmd/std/format.d(4053): 
Deprecation: function foo.Foo.toString is deprecated
Oops
```

Not great. If you use `dmd -de -run`, you'll get:
```
Foo()
```

Notice the deprecations are gone, but so is the usage of the 
`toString` method. Using DMD v2.095.0-beta.1 with `-de` should 
give you the same output, but without `-de`:

```
% ~/dlang/dmd-2.095.0-beta.1/osx/bin/dmd -run foo.d
/Users/geod24/dlang/dmd-2.095.0-beta.1/osx/bin/../../src/phobos/std/format.d(3921): Deprecation: function foo.Foo.toString is deprecated
/Users/geod24/dlang/dmd-2.095.0-beta.1/osx/bin/../../src/phobos/std/format.d(4420):        instantiated from here: hasToString!(Foo, char)
/Users/geod24/dlang/dmd-2.095.0-beta.1/osx/bin/../../src/phobos/std/format.d(4053): Deprecation: function foo.Foo.toString is deprecated
/Users/geod24/dlang/dmd-2.095.0-beta.1/osx/bin/../../src/phobos/std/format.d(4430):        instantiated from here: formatObject!(LockingTextWriter, Foo, char)
/Users/geod24/dlang/dmd-2.095.0-beta.1/osx/bin/../../src/phobos/std/format.d(1875):        instantiated from here: formatValueImpl!(LockingTextWriter, Foo, char)
/Users/geod24/dlang/dmd-2.095.0-beta.1/osx/bin/../../src/phobos/std/format.d(576):        instantiated from here: formatValue!(LockingTextWriter, Foo, char)
/Users/geod24/dlang/dmd-2.095.0-beta.1/osx/bin/../../src/phobos/std/stdio.d(1661):        ... (1 instantiations, -v to show) ...
/Users/geod24/dlang/dmd-2.095.0-beta.1/osx/bin/../../src/phobos/std/stdio.d(4271):        instantiated from here: writefln!(char, Foo)
foo.d(5):        instantiated from here: writefln!(char, Foo)
Oops
```

So the feature works as intended, however `-de` is a dangerous 
trap, as it changes what is instantiated.