sqlx-macros 0.3.0

Macros for SQLx, the rust SQL toolkit. Not intended to be used directly.
Documentation 
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use proc_macro2::Span;
use quote::quote;
use syn::{
    parse_quote, punctuated::Punctuated, token::Comma, Data, DataStruct, DeriveInput, Field,
    Fields, FieldsNamed, Lifetime, Stmt,
};

pub fn expand_derive_from_row(input: &DeriveInput) -> syn::Result<proc_macro2::TokenStream> {
    match &input.data {
        Data::Struct(DataStruct {
            fields: Fields::Named(FieldsNamed { named, .. }),
            ..
        }) => expand_derive_from_row_struct(input, named),

        Data::Struct(DataStruct {
            fields: Fields::Unnamed(_),
            ..
        }) => Err(syn::Error::new_spanned(
            input,
            "tuple structs are not supported",
        )),

        Data::Struct(DataStruct {
            fields: Fields::Unit,
            ..
        }) => Err(syn::Error::new_spanned(
            input,
            "unit structs are not supported",
        )),

        Data::Enum(_) => Err(syn::Error::new_spanned(input, "enums are not supported")),

        Data::Union(_) => Err(syn::Error::new_spanned(input, "unions are not supported")),
    }
}

fn expand_derive_from_row_struct(
    input: &DeriveInput,
    fields: &Punctuated<Field, Comma>,
) -> syn::Result<proc_macro2::TokenStream> {
    let ident = &input.ident;

    let generics = &input.generics;

    let (lifetime, provided) = generics
        .lifetimes()
        .next()
        .map(|def| (def.lifetime.clone(), false))
        .unwrap_or_else(|| (Lifetime::new("'a", Span::call_site()), true));

    let (_, ty_generics, _) = generics.split_for_impl();

    let mut generics = generics.clone();
    generics
        .params
        .insert(0, parse_quote!(R: sqlx::Row<#lifetime>));

    if provided {
        generics.params.insert(0, parse_quote!(#lifetime));
    }

    let predicates = &mut generics.make_where_clause().predicates;

    predicates.push(parse_quote!(&#lifetime str: sqlx::row::ColumnIndex<#lifetime, R>));

    for field in fields {
        let ty = &field.ty;

        predicates.push(parse_quote!(#ty: sqlx::decode::Decode<#lifetime, R::Database>));
        predicates.push(parse_quote!(#ty: sqlx::types::Type<R::Database>));
    }

    let (impl_generics, _, where_clause) = generics.split_for_impl();

    let reads = fields.iter().filter_map(|field| -> Option<Stmt> {
        let id = &field.ident.as_ref()?;
        let id_s = id.to_string();
        let ty = &field.ty;

        Some(parse_quote!(
            let #id: #ty = row.try_get(#id_s)?;
        ))
    });

    let names = fields.iter().map(|field| &field.ident);

    Ok(quote!(
        impl #impl_generics sqlx::row::FromRow<#lifetime, R> for #ident #ty_generics #where_clause {
            fn from_row(row: &R) -> sqlx::Result<Self> {
                #(#reads)*

                Ok(#ident {
                    #(#names),*
                })
            }
        }
    ))
}