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, 49 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.rust/pp.py b/gdb/testsuite/gdb.rust/pp.py
new file mode 100644
index 0000000..57c8cc3
--- /dev/null
+++ b/gdb/testsuite/gdb.rust/pp.py
@@ -0,0 +1,49 @@
+# 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/>.
+
+# This file is part of the GDB testsuite.  It tests python pretty
+# printers.
+
+import re
+import gdb
+
+
+# Printer for Inner.
+class inner_print(object):
+    def __init__(self, val):
+        self.val = val
+
+    def to_string(self):
+        return "x(" + str(self.val["x"]) + ")"
+
+
+def lookup_function(val):
+    "Look-up and return a pretty-printer that can print val."
+
+    # Get the type.
+    type = val.type
+
+    # Get the type name.
+    typename = type.tag
+
+    if typename == None:
+        return None
+
+    if typename == "pp::Inner":
+        return inner_print(val)
+    return None
+
+
+gdb.pretty_printers.append(lookup_function)