[PATCH] Print void types correctly in Rust

[Manish Goregaokar]

Landed as https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=commit;h=921d8f549f9e35d3f83c7b1a381146a7dc1246f4,
with a changelog fix at
https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=commit;h=6763d566a8d30d1ad65dfd060a919c621dad86c4.


Thanks,
-Manish


On Mon, Jun 27, 2016 at 9:22 PM, Manish Goregaokar <manish@mozilla.com> wrote:
> Rust prefers to not specify the return type of a function when it is unit
> (`()`). The type is also referred to as "void" in debuginfo but not in actual
> usage, so we should never be printing "void" when the language is Rust.
>
> gdb/ChangeLog:
>     * rust-lang.c: Print unit types as "()"
>     * rust-lang.c: Omit return type for functions returning unit
>
> gdb/testsuite/ChangeLog:
> 2016-06-27  Manish Goregaokar  <manish@mozilla.com>
>     * gdb.rust/simple.rs: Add test for returning unit in a function
>     * gdb.rust/simple.exp: Add expectation for functions returning unit
> ---
>  gdb/rust-lang.c                   | 22 ++++++++++++++++++----
>  gdb/testsuite/gdb.rust/simple.exp |  1 +
>  gdb/testsuite/gdb.rust/simple.rs  |  7 +++++++
>  3 files changed, 26 insertions(+), 4 deletions(-)
>
> diff --git a/gdb/rust-lang.c b/gdb/rust-lang.c
> index 0c56a0f..2b115ee 100644
> --- a/gdb/rust-lang.c
> +++ b/gdb/rust-lang.c
> @@ -446,7 +446,7 @@ static const struct generic_val_print_decorations
> rust_decorations =
>    " * I",
>    "true",
>    "false",
> -  "void",
> +  "()",
>    "[",
>    "]"
>  };
> @@ -729,13 +729,22 @@ rust_print_type (struct type *type, const char *varstring,
>    if (show <= 0
>        && TYPE_NAME (type) != NULL)
>      {
> -      fputs_filtered (TYPE_NAME (type), stream);
> +      /* Rust calls the unit type "void" in its debuginfo,
> +         but we don't want to print it as that.  */
> +      if (TYPE_CODE (type) == TYPE_CODE_VOID)
> +        fputs_filtered ("()", stream);
> +      else
> +        fputs_filtered (TYPE_NAME (type), stream);
>        return;
>      }
>
>    type = check_typedef (type);
>    switch (TYPE_CODE (type))
>      {
> +    case TYPE_CODE_VOID:
> +      fputs_filtered ("()", stream);
> +      break;
> +
>      case TYPE_CODE_FUNC:
>        /* Delegate varargs to the C printer.  */
>        if (TYPE_VARARGS (type))
> @@ -753,8 +762,13 @@ rust_print_type (struct type *type, const char *varstring,
>        rust_print_type (TYPE_FIELD_TYPE (type, i), "", stream, -1, 0,
>                 flags);
>      }
> -      fputs_filtered (") -> ", stream);
> -      rust_print_type (TYPE_TARGET_TYPE (type), "", stream, -1, 0, flags);
> +      fputs_filtered (")", stream);
> +      /* If it returns unit, we can omit the return type.  */
> +      if (TYPE_CODE (TYPE_TARGET_TYPE (type)) != TYPE_CODE_VOID)
> +      {
> +        fputs_filtered (" -> ", stream);
> +        rust_print_type (TYPE_TARGET_TYPE (type), "", stream, -1, 0, flags);
> +      }
>        break;
>
>      case TYPE_CODE_ARRAY:
> diff --git a/gdb/testsuite/gdb.rust/simple.exp
> b/gdb/testsuite/gdb.rust/simple.exp
> index 88f1c89..4622f75 100644
> --- a/gdb/testsuite/gdb.rust/simple.exp
> +++ b/gdb/testsuite/gdb.rust/simple.exp
> @@ -149,6 +149,7 @@ gdb_test "print self::diff2(8, 9)" " = -1"
>  gdb_test "print ::diff2(23, -23)" " = 46"
>
>  gdb_test "ptype diff2" "fn \\(i32, i32\\) -> i32"
> +gdb_test "ptype empty" "fn \\(\\)"
>
>  gdb_test "print (diff2 as fn(i32, i32) -> i32)(19, -2)" " = 21"
>
> diff --git a/gdb/testsuite/gdb.rust/simple.rs b/gdb/testsuite/gdb.rust/simple.rs
> index 32da580..3d28e27 100644
> --- a/gdb/testsuite/gdb.rust/simple.rs
> +++ b/gdb/testsuite/gdb.rust/simple.rs
> @@ -48,6 +48,12 @@ fn diff2(x: i32, y: i32) -> i32 {
>      x - y
>  }
>
> +// Empty function, should not have "void"
> +// or "()" in its return type
> +fn empty() {
> +
> +}
> +
>  pub struct Unit;
>
>  // This triggers the non-zero optimization that yields a different
> @@ -111,4 +117,5 @@ fn main () {
>
>      println!("{}, {}", x.0, x.1);        // set breakpoint here
>      println!("{}", diff2(92, 45));
> +    empty();
>  }
> --
> 2.8.3