Rewrite #[derive(Queryable)] in derives2

This was fairly recently rewritten, so it should in theory be the most
straightforward derive to port. Unfortunately, due to
rust-lang/rust#47311, it's obnoxiously hard to
actually construct a struct in a derive right now. We have to do hacky
workarounds until that is fixed.

diesel_derives/src/lib.rs

@@ -33,19 +33,13 @@ mod identifiable;
 mod insertable;
 mod model;
 mod query_id;
-mod queryable;
 mod queryable_by_name;
 mod sql_type;
 mod util;
 
 use proc_macro::TokenStream;
 use syn::parse_derive_input;
 
-#[proc_macro_derive(Queryable, attributes(column_name))]
-pub fn derive_queryable(input: TokenStream) -> TokenStream {
-    expand_derive(input, queryable::derive_queryable)
-}
-
 #[proc_macro_derive(QueryableByName, attributes(table_name, column_name, sql_type, diesel))]
 pub fn derive_queryable_by_name(input: TokenStream) -> TokenStream {
     expand_derive(input, queryable_by_name::derive)

diesel_derives/tests/tests.rs

@@ -5,7 +5,6 @@ extern crate diesel;
 #[macro_use]
 extern crate diesel_derives;
 
-mod queryable;
 mod queryable_by_name;
 mod associations;
 mod test_helpers;

diesel_derives2/src/as_changeset.rs

@@ -50,6 +50,7 @@ pub fn derive(item: syn::DeriveInput) -> Result<quote::Tokens, Diagnostic> {
         model.dummy_mod_name("as_changeset"),
         quote!(
             use self::diesel::query_builder::AsChangeset;
+            use self::diesel::prelude::*;
 
             impl #impl_generics AsChangeset for &'update #struct_name #ty_generics
             #where_clause

diesel_derives2/src/field.rs

@@ -54,6 +54,19 @@ pub enum FieldName {
     Unnamed(syn::Index),
 }
 
+impl FieldName {
+    pub fn for_assignment(&self) -> quote::Tokens {
+        match *self {
+            FieldName::Named(mut x) => {
+                // https://github.com/rust-lang/rust/issues/47311
+                x.span = Span::call_site();
+                quote!(#x)
+            }
+            FieldName::Unnamed(ref x) => quote!(#x),
+        }
+    }
+}
+
 impl quote::ToTokens for FieldName {
     fn to_tokens(&self, tokens: &mut quote::Tokens) {
         use proc_macro2::{Spacing, TokenNode, TokenTree};

diesel_derives2/src/lib.rs

@@ -27,6 +27,7 @@ mod model;
 mod util;
 
 mod as_changeset;
+mod queryable;
 
 use diagnostic_shim::*;
 
@@ -36,6 +37,11 @@ pub fn derive_as_changeset(input: TokenStream) -> TokenStream {
     expand_derive(input, as_changeset::derive)
 }
 
+#[proc_macro_derive(Queryable, attributes(column_name))]
+pub fn derive_queryable(input: TokenStream) -> TokenStream {
+    expand_derive(input, queryable::derive)
+}
+
 fn expand_derive(
     input: TokenStream,
     f: fn(syn::DeriveInput) -> Result<quote::Tokens, Diagnostic>,

diesel_derives2/src/queryable.rs

@@ -0,0 +1,53 @@
+use proc_macro2::Span;
+use quote;
+use syn;
+
+use model::*;
+use util::*;
+
+pub fn derive(item: syn::DeriveInput) -> Result<quote::Tokens, Diagnostic> {
+    let model = Model::from_item(&item)?;
+
+    let struct_name = item.ident;
+    let field_ty = model.fields().iter().map(|f| &f.ty).collect::<Vec<_>>();
+    let field_ty = &field_ty;
+    let build_expr = model.fields().iter().enumerate().map(|(i, f)| {
+        let field_name = &f.name.for_assignment();
+        let i: syn::Index = i.into();
+        // Make sure `row` has a `def_site` span
+        let row = quote!(row);
+        // https://github.com/rust-lang/rust/issues/47311
+        let span = Span::call_site();
+        quote_spanned!(span=> #field_name: (#row.#i))
+    });
+
+    let (_, ty_generics, _) = item.generics.split_for_impl();
+    let mut generics = item.generics.clone();
+    generics.params.push(parse_quote!(__DB: diesel::backend::Backend));
+    generics.params.push(parse_quote!(__ST));
+    {
+        let where_clause = generics.where_clause.get_or_insert(parse_quote!(where));
+        where_clause.predicates.push(parse_quote!((#(#field_ty,)*): Queryable<__ST, __DB>));
+    }
+    let (impl_generics, _, where_clause) = generics.split_for_impl();
+
+    Ok(wrap_in_dummy_mod(
+        model.dummy_mod_name("queryable"),
+        quote! {
+            use self::diesel::Queryable;
+
+            impl #impl_generics Queryable<__ST, __DB> for #struct_name #ty_generics
+            #where_clause
+            {
+                type Row = <(#(#field_ty,)*) as Queryable<__ST, __DB>>::Row;
+
+                fn build(row: Self::Row) -> Self {
+                    let row: (#(#field_ty,)*) = Queryable::build(row);
+                    Self {
+                        #(#build_expr,)*
+                    }
+                }
+            }
+        },
+    ))
+}

diesel_derives2/src/util.rs

@@ -12,7 +12,6 @@ pub fn wrap_in_dummy_mod(const_name: Ident, item: Tokens) -> Tokens {
             mod diesel {
                 __diesel_use_everything!();
             }
-            use self::diesel::prelude::*;
             #item
         }
     }

diesel_derives/tests/queryable.rs → diesel_derives2/tests/queryable.rs

@@ -2,7 +2,7 @@ use diesel::dsl::sql;
 use diesel::*;
 use diesel::sql_types::Integer;
 
-use test_helpers::connection;
+use helpers::connection;
 
 #[test]
 fn named_struct_definition() {
@@ -20,7 +20,7 @@ fn named_struct_definition() {
 #[test]
 fn tuple_struct() {
     #[derive(Debug, Clone, Copy, PartialEq, Eq, Queryable)]
-    struct MyStruct(#[column_name(foo)] i32, #[column_name(bar)] i32);
+    struct MyStruct(#[column_name = "foo"] i32, #[column_name = "bar"] i32);
 
     let conn = connection();
     let data = select(sql::<(Integer, Integer)>("1, 2")).get_result(&conn);

diesel_derives2/tests/tests.rs

@@ -11,3 +11,4 @@ mod helpers;
 mod schema;
 
 mod as_changeset;
+mod queryable;