Enable DDoc Markdown by default

[wilzbach]

Markdown support has been in preview for more than a year and is used for the official docs (see e.g. #9645).
It's time to enable it by default. If folks encounter issues, there will be -revert=markdown for a while.

FYI @dgileadi

[dlang-bot]

Thanks for your pull request, @wilzbach!

Bugzilla references

Your PR doesn't reference any Bugzilla issue.

If your PR contains non-trivial changes, please reference a Bugzilla issue or create a manual changelog.

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "master + dmd#11654"

[wilzbach]

Druntime and Phobos are compiled with -de, so this must be done as a multi-stage PR iteration.

[Geod24]

Nice! I was wondering today when should the other -preview switch be moved forward. Good to see some features being enabled.

[wilzbach]

Nice! I was wondering today when should the other -preview switch be moved forward. Good to see some features being enabled.

Most -preview switches are problematic to enable, because they either break code or aren't fully finished or don't even compile druntime/Phobos, but this is one of the few that I think we can easily move ahead.

[wilzbach]

Otherwise it generates:

  <p class="para">
    Create inclusive invariant for struct/class by aggregating
 all the invariants in invs[].
      void __invariant() const [pure nothrow @trusted]
      {
          invs<a href="">0</a>, invs<a href="">1</a>, ...;
      }
  </p>

[wilzbach]

(Windows failure is unrelated - see #11653)

[Geod24]

Actually, I don't think this description is enough, because:

• Let's not kid ourselves, most users don't use -preview. So re-stating some informations on it (where the documentation can be found, and an overview of the features / changes) is IMO important.
• It's also important to have more than a one-liner for such an important feature. I know many users have asked for it over the year, and we should be a bit more proactive in marketing the good changes we're doing.
• It's not a usual practice, so this is only a suggestion, but I would add a thank you note to @dgileadi for championing this.

[wilzbach]

Fair enough. I'm really lazy with changelog entries. I updated this one.

It's not a usual practice, so this is only a suggestion, but I would add a thank you note to @dgileadi for championing this.

Great idea! We should make this the usual practice ;-)

[Geod24]

ERROR: Newly generated header file (/home/circleci/dmd/generated/linux/release/64/frontend.h) doesn't match with the reference header file (/home/circleci/dmd/src/dmd/frontend.h)

DETAILS:

diff --git a/home/circleci/dmd/src/dmd/frontend.h b/home/circleci/dmd/generated/linux/release/64/frontend.h
index 172f7dae3..b707a27c4 100644
--- a/home/circleci/dmd/src/dmd/frontend.h
+++ b/home/circleci/dmd/generated/linux/release/64/frontend.h

Heh

[wilzbach]

ERROR: Newly generated header file (/home/circleci/dmd/generated/linux/release/64/frontend.h) doesn't match with the reference header file (/home/circleci/dmd/src/dmd/frontend.h)

Yeah, this is enforced now and should hopefully avoid silent C++ header breakage.
A bit silly for this PR as frontend.h can't be used yet and the current C++ headers don't provide a constructor for Params, but updating isn't hard (./build.d cxx-headers-test AUTO_UPDATE=1).

[Geod24]

Let's