Change tuple Debug impls to use builders

[sfackler]

This does change the Debug output for 1-tuples to (foo) instead of (foo,) but I don't think it's that big of a deal.

r? @alexcrichton

[bluss]

Since it's using a macro, we could special case the unary tuple, so that we get the comma anyway? (1) is consistent with tuple structs, but I think it's a bit weird.

[alexcrichton]

Yeah I think I'd prefer to keep the trailing comma on 1-tuples, but other than that r=me

[nagisa]

Would be nice to keep Debug output as close to something that compiles. let x: (i32,) = (0); // note the missing comma does not.

[sfackler]

Updated

[alexcrichton]

In the interest of not having lingering unstable methods, could this do what @bluss mentioned and special case the 1-tuple case?

[sfackler]

The machinery involved to properly handle the pretty case is involved enough (e.g. see fmt::builders::PadAdapter) that this is the lowest impact implementation I can see.

[bluss]

Yes on a closer look it's not easy, I trust what you think is best sfackler

[alexcrichton]

Wouldn't it be something along the lines of:

fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
    if f.alternate_flag_enabled() {
        write!(f, "({:#?},)", self.0)
    } else {
        write!(f, "({:?},)", self.0)
    }
}

[sfackler]

That'd generate

(Foo {
    bar: hi
},)

but the builder would generate

(
    Foo {
        bar: hi
    },
)

[alexcrichton]

Hm ok, seems fine then.

@bors: r+ b0ab164

[bors]

⌛ Testing commit b0ab164 with merge 0c05219...

[bors]

☀️ Test successful - auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-64-nopt-t, auto-linux-64-opt, auto-linux-64-x-android-t, auto-mac-32-opt, auto-mac-64-nopt-t, auto-mac-64-opt, auto-win-gnu-32-nopt-t, auto-win-gnu-32-opt, auto-win-gnu-64-nopt-t, auto-win-gnu-64-opt