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

[Manish Goregaokar <manish at mozilla dot com>]

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