Re: [PATCH] Fix handling of discriminantless univariant enums in Rust

Manish Goregaokar
2016-10-30T03:06:06Z

The same test works fine with a univariant tuple enum and
STRUCTOP_ANONYMOUS fwiw. (added a univariant_anon test to my local
patch)
-Manish

On Sat, Oct 29, 2016 at 7:58 PM, Manish Goregaokar <manish@mozilla.com> wrote:
> `print univariant.a` works for me.
>
> New patch (fixed style, added univariant.a test)
>
>
> 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 | 3 +++
> gdb/testsuite/gdb.rust/simple.rs | 6 ++++++
> 3 files changed, 21 insertions(+), 1 deletion(-)
>
> diff --git a/gdb/rust-lang.c b/gdb/rust-lang.c
> index 82cd3f9..7b1ff8a 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..c9e8e57 100644
> --- a/gdb/testsuite/gdb.rust/simple.exp
> +++ b/gdb/testsuite/gdb.rust/simple.exp
> @@ -103,6 +103,9 @@ gdb_test_sequence "ptype z" "" {
> }
> gdb_test "print z.1" " = 8"
>
> +gdb_test "print univariant" " = simple::Univariant::Foo{a: 1}"
> +gdb_test "print univariant.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
>
> -Manish
>
>
> On Sat, Oct 29, 2016 at 7:52 PM, Tom Tromey <tom@tromey.com> wrote:
>>>>>>> "Tom" == Tom Tromey <tom@tromey.com> writes:
>>
>> Tom> Also, I suspect this will wind up doing the wrong thing in the
>> Tom> STRUCTOP_ANONYMOUS case in rust_evaluate_subexp. In particular I wonder
>> Tom> if an additional "print univariant.0.a" test will work correctly?
>>
>> Oh duh, I see that this isn't a correct counter-example.
>> What about just "print univariant.a"?
>> It seems to me that this will hit this:
>>
>> start = disr.is_encoded ? 0 : 1;
>>
>> ... choosing 1 here, but:
>>
>> for (i = start; i < TYPE_NFIELDS (variant_type); i++)
>>
>> ... failing this because TYPE_NFIELDS == 1; and then:
>>
>> if (i == TYPE_NFIELDS (variant_type))
>> /* We didn't find it. */
>> error(_("Could not find field %s of struct variant %s"),
>>
>> Tom