[PATCH] Fix handling of discriminantless univariant enums in Rust

[Manish Goregaokar <manish at mozilla dot com>]

Fixes an issue caught by TimNN in https://github.com/rust-lang/rust/pull/37410


From: Manish Goregaokar <manish@mozilla.com>
Date: Thu, 27 Oct 2016 16:46:34 -0700
Subject: Fix handling of discriminantless univariant enums in Rust

2016-10-27  Manish Goregaokar  <manish@mozilla.com>

gdb/ChangeLog:
    * rust-lang.c (rust_get_disr_info): Treat univariant enums
      without discriminants as encoded enums with a real field

gdb/testsuite/ChangeLog:
    * simple.rs: Add test for univariant enums without discriminants
    * simple.exp: Add test expectations
---
 gdb/rust-lang.c                   | 13 ++++++++++++-
 gdb/testsuite/gdb.rust/simple.exp |  2 ++
 gdb/testsuite/gdb.rust/simple.rs  |  6 ++++++
 3 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/gdb/rust-lang.c b/gdb/rust-lang.c
index 82cd3f9..9d13353 100644
--- a/gdb/rust-lang.c
+++ b/gdb/rust-lang.c
@@ -194,7 +194,18 @@ rust_get_disr_info (struct type *type, const
gdb_byte *valaddr,
      has changed its debuginfo format.  */
       error (_("Could not find enum discriminant field"));
     }
-
+  else if (TYPE_NFIELDS (type) == 1) {
+    /* Sometimes univariant enums are encoded without a
+    discriminant. In that case, treating it as an encoded enum
+    with the first field being the actual type works.  */
+    const char* field_name = TYPE_NAME (TYPE_FIELD_TYPE (type, 0));
+    ret.name = concat (TYPE_NAME (type), "::",
+                       rust_last_path_segment (field_name),
+                       (char *) NULL);
+    ret.field_no = RUST_ENCODED_ENUM_REAL;
+    ret.is_encoded = 1;
+    return ret;
+  }
   if (strcmp (TYPE_FIELD_NAME (disr_type, 0), "RUST$ENUM$DISR") != 0)
     error (_("Rust debug format has changed"));

diff --git a/gdb/testsuite/gdb.rust/simple.exp
b/gdb/testsuite/gdb.rust/simple.exp
index 5e00b03..dbfc88a 100644
--- a/gdb/testsuite/gdb.rust/simple.exp
+++ b/gdb/testsuite/gdb.rust/simple.exp
@@ -103,6 +103,8 @@ gdb_test_sequence "ptype z" "" {
 }
 gdb_test "print z.1" " = 8"

+gdb_test "print univariant" " = simple::Univariant::Foo{a: 1}"
+
 gdb_test_sequence "ptype simple::ByeBob" "" {
     " = struct simple::ByeBob \\("
     "  i32,"
diff --git a/gdb/testsuite/gdb.rust/simple.rs b/gdb/testsuite/gdb.rust/simple.rs
index eeff3d7..b2e29ae 100644
--- a/gdb/testsuite/gdb.rust/simple.rs
+++ b/gdb/testsuite/gdb.rust/simple.rs
@@ -63,6 +63,10 @@ enum SpaceSaver {
     Nothing,
 }

+enum Univariant {
+    Foo {a: u8}
+}
+
 fn main () {
     let a = ();
     let b : [i32; 0] = [];
@@ -93,6 +97,8 @@ fn main () {
     let y = HiBob {field1: 7, field2: 8};
     let z = ByeBob(7, 8);

+    let univariant = Univariant::Foo {a : 1};
+
     let slice = &w[2..3];
     let fromslice = slice[0];
     let slice2 = &slice[0..1];
-- 
2.10.1