Fix Python pretty-printing bug in Rust

An upstream Rust bug notes notes that the Python pretty-printing
feature is broken for values that appear as members of certain types
in Rust.

The bug here is that some of the Rust value-printing code calls
value_print_inner, a method on rust_language.  This bypasses the
common code that calls into Python.

I'm checking this in.

gdb/ChangeLog
2021-05-14  Tom Tromey  <tom@tromey.com>

	* rust-lang.c (rust_language::val_print_struct)
	(rust_language::print_enum): Use common_val_print, not
	value_print_inner.

gdb/testsuite/ChangeLog
2021-05-14  Tom Tromey  <tom@tromey.com>

	* gdb.rust/pp.exp: New file.
	* gdb.rust/pp.py: New file.
	* gdb.rust/pp.rs: New file.

1 files changed, 26 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.rust/pp.rs b/gdb/testsuite/gdb.rust/pp.rs
new file mode 100644
index 0000000..23e85af
--- /dev/null
+++ b/gdb/testsuite/gdb.rust/pp.rs
@@ -0,0 +1,26 @@
+// Copyright (C) 2021 Free Software Foundation, Inc.
+
+// This program is free software; you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation; either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+#![allow(dead_code)]
+#![allow(unused_variables)]
+#![allow(unused_assignments)]
+
+struct Inner{ x : u8 }
+struct Outer(Inner);
+
+fn main () {
+    let outer = Outer(Inner{x: 5});
+    println!("{}", outer.0.x);        // set breakpoint here
+}