newtype_index macro `DEBUG_FORMAT = custom` not working

[spastorino]

I'm trying to change DefIndex to be defined using newtype_index and calling newtype_index macro this way ...

newtype_index!(DefIndex
    {
        DEBUG_FORMAT = custom

        const DEF_INDEX_HI_START = 1 << 31,

        const CRATE_DEF_INDEX = 0,
    });

Does not work.

/cc @Nashenas88 @nikomatsakis

[durka]

Are you just missing a comma after the DEBUG_FORMAT line? It seems to be expected:

rust/src/librustc_data_structures/indexed_vec.rs

Lines 289 to 296 in 98e4b68

	// Replace existing default for debug_format
	(@derives [$($derives:ident,)*]
	@pub [$($pub:tt)*]
	@type [$type:ident]
	@max [$max:expr]
	@debug_format [$_debug_format:expr]
	DEBUG_FORMAT = $debug_format:expr,
	$($tokens:tt)*) => (

[spastorino]

Yeah I wasn't paying a lot of attention to the macro definition, anyway ... with comma ...

error: format argument must be a string literal.
  --> src/librustc/hir/def_id.rs:91:24
   |
91 |         DEBUG_FORMAT = custom,
   |                        ^^^^^^

With comma and making custom a string ....

error: argument never used
  --> src/librustc/hir/def_id.rs:89:1
   |
89 | / newtype_index!(DefIndex
90 | |     {
91 | |         DEBUG_FORMAT = "custom",
92 | |
...  |
95 | |         const CRATE_DEF_INDEX = 0,
96 | |     });
   | |_______^

[spastorino]

So ... or either I don't understand how to use the macro or there's a bug somewhere.

[durka]

Yes, I think there is a bug. There is a base case for custom debug format but no rule for parsing that from the macro input like there is for ENCODABLE.

rust/src/librustc_data_structures/indexed_vec.rs

Lines 93 to 97 in 98e4b68

	// base case for handle_debug where format is custom. No Debug implementation is emitted.
	(@handle_debug
	@derives [$($_derives:ident,)*]
	@type [$type:ident]
	@debug_format [custom]) => ();

[spastorino]

@durka, actually after checking, the case you mentioned is not the right match arm.

We should be going through

rust/src/librustc_data_structures/indexed_vec.rs

Lines 93 to 97 in 98e4b68

	// base case for handle_debug where format is custom. No Debug implementation is emitted.
	(@handle_debug
	@derives [$($_derives:ident,)*]
	@type [$type:ident]
	@debug_format [custom]) => ();

[durka]

Yeah that is the one I linked. But that's the end of the macro, there needs to be another parsing rule that eats DEBUG_FORMAT = custom,.

[spastorino]

@durka exactly!

[durka]

OK, I figured out what the issue is. Parsing DEBUG_FORMAT = custom is actually fine since custom is a valid expr. However once you've parsed something into an expr you can't "look inside" it again -- matching it against the ident custom on line 97 doesn't work.

What needs to be done I believe is changing $debug_format:expr to $debug_format:tt everywhere in the macro. This should still work as a string literal is a single token, and it will preserve custom as a token that can be matched again.

[spastorino]

After changing what you've said I'm getting ...

error: no rules expected the token `derives`
  --> src/librustc/hir/def_id.rs:89:1
   |
89 | / newtype_index!(DefIndex
90 | |     {
91 | |         DEBUG_FORMAT custom
92 | |
...  |
98 | |         const CRATE_DEF_INDEX = 0,
99 | |     });
   | |_______^
   |
   = note: this error originates in a macro outside of the current crate

error: aborting due to previous error

error: Could not compile `rustc`.

[durka]

Now you have DEBUG_FORMAT custom instead of DEBUG_FORMAT = custom,? Or the error output is just mangling your source? I can take a look at your branch directly if you want.

[spastorino]

Hey @durka, thanks, I think it's working now. I'm testing it and will open a PR if everything is OK. Thanks for the tips, at some point I'd need to read at least something about macros ;).