Improved constant values generated code (2)

[GilShoshan94]

Hi @illicitonion and @danielhenrymantilla,

I discovered this crate yesterday and it's seems perfect for me. Thank you !
I am using the last version 0.5.7.
I ran cargo expand on my code to better understand what it is doing.

The result was quite "ugly" (shown bellow).
I looked in the past issues and found #12 that enhances exactly that.
I tested at the 0.4.2 version and indeed the expansion was "pretty".

Then I tried to find at which version the expansion got "ugly" again.
It happended at the 0.5.0 version.

I am looking at the code right now to see how to fix that.
I never wrote macro so it's a bit cryptic to me....

The "ugly" expansion:

impl ::num_enum::TryFromPrimitive for EncodingFormat {
        type Primitive = u8;
        const NAME: &'static str = "EncodingFormat";
        fn try_from_primitive(
            number: Self::Primitive,
        ) -> ::core::result::Result<Self, ::num_enum::TryFromPrimitiveError<Self>> {
            #![allow(non_upper_case_globals)]
            const Postcard__num_enum_0__: u8 = 2;
            const Json__num_enum_0__: u8 = u8::wrapping_add(2, 1);
            const MessagePack__num_enum_0__: u8 = u8::wrapping_add(
                u8::wrapping_add(2, 1),
                1,
            );
            const Pickle__num_enum_0__: u8 = u8::wrapping_add(
                u8::wrapping_add(u8::wrapping_add(2, 1), 1),
                1,
            );
            const BSON__num_enum_0__: u8 = u8::wrapping_add(
                u8::wrapping_add(u8::wrapping_add(u8::wrapping_add(2, 1), 1), 1),
                1,
            );
            const CBOR__num_enum_0__: u8 = u8::wrapping_add(
                u8::wrapping_add(
                    u8::wrapping_add(u8::wrapping_add(u8::wrapping_add(2, 1), 1), 1),
                    1,
                ),
                1,
            );
            const CSV__num_enum_0__: u8 = u8::wrapping_add(
                u8::wrapping_add(
                    u8::wrapping_add(
                        u8::wrapping_add(u8::wrapping_add(u8::wrapping_add(2, 1), 1), 1),
                        1,
                    ),
                    1,
                ),
                1,
            );
            const Bencode__num_enum_0__: u8 = u8::wrapping_add(
                u8::wrapping_add(
                    u8::wrapping_add(
                        u8::wrapping_add(
                            u8::wrapping_add(
                                u8::wrapping_add(u8::wrapping_add(2, 1), 1),
                                1,
                            ),
                            1,
                        ),
                        1,
                    ),
                    1,
                ),
                1,
            );
            #[deny(unreachable_patterns)]
            match number {
                Postcard__num_enum_0__ => ::core::result::Result::Ok(Self::Postcard),
...

The "pretty" expansion:

impl ::num_enum::TryFromPrimitive for EncodingFormat {
        type Primitive = u8;
        const NAME: &'static str = "EncodingFormat";
        fn try_from_primitive(
            number: Self::Primitive,
        ) -> ::core::result::Result<Self, ::num_enum::TryFromPrimitiveError<Self>> {
            #![allow(non_upper_case_globals)]
            const Postcard: u8 = 2;
            const Json: u8 = u8::wrapping_add(Postcard, 1);
            const MessagePack: u8 = u8::wrapping_add(Json, 1);
            const Pickle: u8 = u8::wrapping_add(MessagePack, 1);
            const BSON: u8 = u8::wrapping_add(Pickle, 1);
            const CBOR: u8 = u8::wrapping_add(BSON, 1);
            const CSV: u8 = u8::wrapping_add(CBOR, 1);
            const Bencode: u8 = u8::wrapping_add(CSV, 1);
            match number {
                Postcard => ::core::result::Result::Ok(EncodingFormat::Postcard),
...

[GilShoshan94]

I looked at the proc macro code and I don't really get it to be honest... I can follow a bit what's it's going on but cannot edit with confidence...

In the code, from line 393 to line 405

We have:

...
                variants.push(VariantInfo {
                    ident,
                    attr_spans,
                    is_default,
                    is_catch_all,
                    canonical_value,
                    alternative_values,
                });

                next_discriminant = parse_quote! {
                    #repr::wrapping_add(#discriminant, 1)
                };
            }
...

It seems to me that changing #discriminant to #ident would do the trick...

[GilShoshan94]

Ok I tried it and it and it first failed because the value got moved into variants (move occurs because ident has type proc_macro2::Ident, which does not implement the Copy trait`)

So I cloned ident and now it worked !

Here the new code:

...
                let ident_clone = ident.clone();
                variants.push(VariantInfo {
                    ident,
                    attr_spans,
                    is_default,
                    is_catch_all,
                    canonical_value,
                    alternative_values,
                });

                next_discriminant = parse_quote! {
                    #repr::wrapping_add(#ident_clone, 1)
                };
            }
...

And this is the "pretty" expansion:

    impl ::num_enum::TryFromPrimitive for EncodingFormat {
        type Primitive = u8;
        const NAME: &'static str = "EncodingFormat";
        fn try_from_primitive(
            number: Self::Primitive,
        ) -> ::core::result::Result<Self, ::num_enum::TryFromPrimitiveError<Self>> {
            #![allow(non_upper_case_globals)]
            const Postcard__num_enum_0__: u8 = 2;
            const Json__num_enum_0__: u8 = u8::wrapping_add(Postcard, 1);
            const MessagePack__num_enum_0__: u8 = u8::wrapping_add(Json, 1);
            const Pickle__num_enum_0__: u8 = u8::wrapping_add(MessagePack, 1);
            const BSON__num_enum_0__: u8 = u8::wrapping_add(Pickle, 1);
            const CBOR__num_enum_0__: u8 = u8::wrapping_add(BSON, 1);
            const CSV__num_enum_0__: u8 = u8::wrapping_add(CBOR, 1);
            const Bencode__num_enum_0__: u8 = u8::wrapping_add(CSV, 1);
            #[deny(unreachable_patterns)]
            match number {
                Postcard__num_enum_0__ => ::core::result::Result::Ok(Self::Postcard),
...

[GilShoshan94]

I am by no mean sure if my solution breaks anything. I don't really get the nitty gritty details yet.
Any feedback is welcome.

[GilShoshan94]

PR #89 resolves this. Closing the issue.

Also now it's even cleaner as the value are calculated before code generation, so no wrapping_add() even.