Change how to format a data type with a record constructor

[toku-sa-n]

After thinking a little, I've decided to specialize the case where a data or a newtype declaration has only one record constructor. It breaks the consistency, but I don't think people will define multiple record constructors often.

Fixes: #546

@mihaimaruseac By the way, could you merge PRs by squashing? It will make the commit log more readable. Of course, I can squash commits by myself, but it'll require force-pushing and I want to avoid it as I may make a mistake. Squashing-merging is easy and handy, I think.

[mihaimaruseac]

Unfortunately, squashing has two effects which make it undesirable:

• impossible to bisect over the commits on the branch since they're now all in one unit
• reverting the PR results in an "unverified" commit

[toku-sa-n]

impossible to bisect over the commits on the branch since they're now all in one unit

I don't think this is a problem. We can still bisect to find a PR that introduced a bug and, if necessary, continue bisecting on the PR's branch to find the exact commit. It may be an extra, but tiny work. Rather, since all commits related to a PR are squashed, we can get a meaningful diff and easily access to the PR for the underlying discussion.

reverting the PR results in an "unverified" commit

I'm surprised by this behavior; I expected all commits created on GitHub would automatically be GPG-signed. Actually I don't care even if a commit is not signed, though.

Overall, I don't think squashing a PR has large problems. But if you are concerned about them, I don't have any objections to merge (not squash) PRs.

[mihaimaruseac]

reverting the PR results in an "unverified" commit

I'm surprised by this behavior; I expected all commits created on GitHub would automatically be GPG-signed. Actually I don't care even if a commit is not signed, though.

Yeah, I think it is a bug in GitHub here.

I am concerned about signed commits, is a step for supply-chain security.

But we also have very little need to revert PRs, so let's go with squashing.