Rusteceans of the Fediverse, can you help me with a declarative macro problem?

[steffo@a.junimo.party]

@slatian something like this?

pub trait Table {
    fn sql_safe_table_name(&self) -> &'static str;
}

pub trait Field {
    fn sql_safe_field_name(&self) -> &'static str;
}

macro_rules! sql_schema {
    {
        $schema_name:ident,
        $(
            enum $table_name:ident = $table_value:literal {
                $( $field_name:ident = $field_value:literal ),*
            }
        )*
    } => {
        pub enum $schema_name {
            $( $table_name ),*
        }

        impl Table for $schema_name {
            fn sql_safe_table_name(&self) -> &'static str {
                match self {
                    $( $schema_name::$table_name => $table_value ),*
                }
            }
        }

        $(
            // it's not possible to concatenate things to identifiers without the use of a proc macro
            // so we just re-use $table_name
            pub enum $table_name {
                $( $field_name ),*
            }

            impl Field for $table_name {
                fn sql_safe_field_name(&self) -> &'static str {
                    match self {
                        $( $table_name::$field_name => $field_value ),*
                    }
                }
            }
        )*
    }
}

sql_schema! {
    BaseTable,
    enum MimeParameter = "mime_parameter" {
        Key = "key",
        MimeParameterId = "mime_parameter_id"
    }
    enum Mimetype = "mimetype" {
        Charset = "charset"
         // …
    }
}

you can use cargo expand to see what it generates

[slatian@pleroma.envs.net]

@steffo@a.junimo.party It took a while for me to wrap my Brain around this :drgn_sparkle: <- didn't expect it to be that … simple and especially readable.

Given that I can almost 1:1 copy this into criterium (licensed LGPL-3.0-only): May I? If yes, what name do you want in the copyright header?

[steffo@a.junimo.party]

@slatian sure! you can add Stefano Pigozzi <me@steffo.eu> to the contributors section of Cargo.toml if you want, but dw, it's just a snippet of code that fit in a fedi post

[steffo@a.junimo.party]

@slatian a thing to be aware of, $(),* does not allow trailing commas, so this would work

    enum Mimetype = "mimetype" {
        Charset = "charset"
    }

but this would give a weird error

    enum Mimetype = "mimetype" {
        Charset = "charset",
    }

[slatian@pleroma.envs.net]

@steffo@a.junimo.party

The optional comma could just be eaten by a $(…),* $(,)?

Or am I missing something? (I don't write a lot of macros.)

[steffo@a.junimo.party]

@slatian yep

[steffo@a.junimo.party]

Questo post è eliminato!

[steffo@a.junimo.party]

Questo post è eliminato!

[steffo@a.junimo.party]

@slatian wait no i remembered correctly

Each repetition in the transcriber must contain at least one metavariable to decide how many times to expand it.

[slatian@pleroma.envs.net]

This is what I ended up with:

https://codeberg.org/unobtanium/criterium/src/branch/main/src/sql/schema_macro.rs

Huge Thank You goes to @steffo@a.junimo.party :drgn_heart: