debuginfo: Add GDB pretty printers for slices, Vec<>, and String.

[michaelwoerister]

Rust:  let slice: &[i32] = &[0, 1, 2, 3];
GDB:   $1 = &[i32](len: 4) = {0, 1, 2, 3}

Rust:  let vec = vec![4, 5, 6, 7];
GDB:   $2 = Vec<u64>(len: 4, cap: 4) = {4, 5, 6, 7}

Rust:  let str_slice = "IAMA string slice!";
GDB:   $3 = "IAMA string slice!"

Rust:  let string = "IAMA string!".to_string();
GDB:   $4 = "IAMA string!"

Neat!

[rust-highfive]

r? @pcwalton

(rust_highfive has picked a reviewer for you, use r? to override)

[alexcrichton]

@bors: r+ 90fc28d

Nice!

[Manishearth]

👯

[eddyb]

I wonder if it would be possible for &[i32](len: 4) to be printed as &[i32; 4] instead, as if unsizing was being reversed.

[michaelwoerister]

@eddyb We could do that but it would be kind of lying about the type, wouldn't it?

[eddyb]

I guess... I prefer {len: 4, cap: 4} for what it's worth, but that's really unimportant.

[michaelwoerister]

I guess... I prefer {len: 4, cap: 4} for what it's worth, but that's really unimportant.

Yes, I think I'll do some kind of informal poll in the forum about what the actual rendering should look like.