Add bundled GDB pretty-printers

[artemmukhin]

Add bundled GDB pretty-printers.

Now it supports:

• struct, tuple
• str, String, OsString (with UTF-8 support)
• Vec, VecDeque
• BTreeSet, BTreeMap (thanks, @tromey!)
• Rc, Arc
• Cell, Ref, RefMut, RefCell

Fixes #3357

There are some problems with enums because of wrong DWARF codes in rustc's codegen (it affects default rustc pretty-printers too); I'm going to fix it after the next rustc release.

[tromey]

There are some problems with enums because of wrong DWARF codes in rustc's codegen

See rust-lang/rust#54004. If there's a bug, I definitely want to know about it -- but I suspect instead what is happening is that the new debuginfo is confusing the pretty-printers. gdb 8.2 understands the new DWARF and consequently I disabled some of the default pretty-printers in rust-lang/rust#55767.

[tromey]

... also I wonder if I need to fix https://sourceware.org/bugzilla/show_bug.cgi?id=20163, to allow varobjs to work better with rust enums.

[artemmukhin]

@tromey Actually, I meant that the stable Rust toolchain has some problems. I'm aware of your progress on DWARF generation and it looks great on gdb 8.2 with Rust nightly. Consider such code:

enum E { A, B(i32, i32), C { x: i32, y: i32, z: i32} }
let a = E::A;
let b = E::B(42, 123);
let c = E::C { x: 10, y: 20, z: 30 };

gdb 8.2 (without any pretty-printers) prints this enum correctly:

(gdb) p a
$2 = my::E::A
(gdb) p b
$1 = my::E::B(42, 123)
(gdb) p c
$3 = my::E::C{x: 10, y: 20, z: 30}

However, CLion's output is not as good:

Would you happen to know why that might be? Maybe CLion (and probably other Rust IDEs) needs to support some new gdb features related to discriminated unions?

[tromey]

Maybe CLion (and probably other Rust IDEs) needs to support some new gdb features related to discriminated unions?

Assuming CLion is using MI varobjs (I didn't look so I don't know...) then it is that gdb bug I mentioned earlier -- basically varobj has to be taught a bit about discriminated unions.

[artemmukhin]

@tromey OK, I will be watching this gdb bug, thanks!

[Undin]

@ortem Could you rebase onto master?

[artemmukhin]

bors try

[bors]

try

Build failed

• continuous-integration/travis-ci/push

[artemmukhin]

bors r+

[bors]

Build failed

• continuous-integration/appveyor/branch

[artemmukhin]

bors retry

[bors]

Build failed (retrying...)

• continuous-integration/travis-ci/push

[bors]

Build succeeded

• continuous-integration/appveyor/branch
• continuous-integration/travis-ci/push