The dmd test suite is supposed to test dmd before moving on to compiling Phobos. This technique makes porting dmd to new platforms much easier. Unfortunately, many dependencies on Phobos have crept in. I've removed some:

  https://github.com/dlang/dmd/pull/9633
  https://github.com/dlang/dmd/pull/9635

If you're looking for a way to help out, there's plenty of opportunity there!

For a more challenging fix,

  test/runnable/test_cdcmp.d

On Wednesday, 17 April 2019 at 09:47:58 UTC, Walter Bright wrote:
> For a more challenging fix,
>
>   test/runnable/test_cdcmp.d

Rewriting that to not use Phobos looks like a complete waste of time. I suggest to simply flag the tests that require Phobos, and provide the option to run only those tests that do not require Phobos. I'm sure the coverage will still be good enough to facilitate porting a functional compiler that is then capable of building Phobos and running the rest of the tests.

On Friday, 19 April 2019 at 21:05:23 UTC, Vladimir Panteleev wrote:
> On Wednesday, 17 April 2019 at 09:47:58 UTC, Walter Bright wrote:
>> For a more challenging fix,
>>
>>   test/runnable/test_cdcmp.d
>
> Rewriting that to not use Phobos looks like a complete waste of time.

Yes, especially because it doesn't use Phobos at all when run through the testsuite ;-)

On 4/19/2019 2:05 PM, Vladimir Panteleev wrote:
> On Wednesday, 17 April 2019 at 09:47:58 UTC, Walter Bright wrote:
>> For a more challenging fix,
>>
>>   test/runnable/test_cdcmp.d
> 
> Rewriting that to not use Phobos looks like a complete waste of time. I suggest to simply flag the tests that require Phobos, and provide the option to run only those tests that do not require Phobos. I'm sure the coverage will still be good enough to facilitate porting a functional compiler that is then capable of building Phobos and running the rest of the tests.
> 

Many of the tests simply use writefln instead of printf.