[PATCH] Fix crash with "finish" in Rust

[Tom Tromey <tom@tromey.com>]

PR rust/30090 points out that a certain "finish" in a Rust program
will cause gdb to crash.  This happens due to some confusion about
field indices in rust_language::print_enum.  The fix is to use
value_primitive_field so that the correct type can be passed; other
spots in rust-lang.c already do this.

Note that the enclosed test case comes with an xfail.  This is needed
because for this function, rustc doesn't follow the platform ABI.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30090
---
 gdb/rust-lang.c                   |  2 +-
 gdb/testsuite/gdb.rust/finish.exp | 39 +++++++++++++++++++++++++++++++
 gdb/testsuite/gdb.rust/finish.rs  | 30 ++++++++++++++++++++++++
 3 files changed, 70 insertions(+), 1 deletion(-)
 create mode 100644 gdb/testsuite/gdb.rust/finish.exp
 create mode 100644 gdb/testsuite/gdb.rust/finish.rs

diff --git a/gdb/rust-lang.c b/gdb/rust-lang.c
index f2017f95211..5b743b9e56b 100644
--- a/gdb/rust-lang.c
+++ b/gdb/rust-lang.c
@@ -470,7 +470,7 @@ rust_language::print_enum (struct value *val, struct ui_file *stream,
     }
 
   int variant_fieldno = rust_enum_variant (type);
-  val = value_field (val, variant_fieldno);
+  val = value_primitive_field (val, 0, variant_fieldno, type);
   struct type *variant_type = type->field (variant_fieldno).type ();
 
   int nfields = variant_type->num_fields ();
diff --git a/gdb/testsuite/gdb.rust/finish.exp b/gdb/testsuite/gdb.rust/finish.exp
new file mode 100644
index 00000000000..ab0250df277
--- /dev/null
+++ b/gdb/testsuite/gdb.rust/finish.exp
@@ -0,0 +1,39 @@
+# Copyright (C) 2023 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/>.
+
+# Test a certain 'finish' in Rust.
+
+load_lib rust-support.exp
+require allow_rust_tests
+
+standard_testfile .rs
+if {[prepare_for_testing "failed to prepare" $testfile $srcfile {debug rust}]} {
+    return -1
+}
+
+set line [gdb_get_line_number "BREAK"]
+if {![runto ${srcfile}:$line]} {
+    untested "could not run to breakpoint"
+    return -1
+}
+
+# This 'finish' used to crash.  See PR rust/30090.  Also, this does
+# not currently print the correct value, because rustc does not use
+# the standard ABI here.  This is being tracked here:
+# https://github.com/rust-lang/rust/issues/85641
+setup_xfail *-*-*
+gdb_test "finish" [string_to_regexp " = finish::MyResult::Some(97)"]
+gdb_test "next"
+gdb_test "print dei" [string_to_regexp " = finish::MyResult::Some(97)"]
diff --git a/gdb/testsuite/gdb.rust/finish.rs b/gdb/testsuite/gdb.rust/finish.rs
new file mode 100644
index 00000000000..e9dfcd89b0f
--- /dev/null
+++ b/gdb/testsuite/gdb.rust/finish.rs
@@ -0,0 +1,30 @@
+// Copyright (C) 2023 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(warnings)]
+
+enum MyResult {
+    None,
+    Some(u32)
+}
+
+fn return_some() -> MyResult {
+    MyResult::Some(97)  // BREAK
+}
+
+fn main() {
+    let dei = return_some();
+    let another = return_some();
+}
-- 
2.39.1