Allow structs to be annotated with #[table_name="foo"]

This is related to #86, where we are not properly inferring the table
name for some structs. While I do want to actually fix some of the cases
in that issue, it's also been pointed out that we don't handle any edge
cases for pluralization.

I might improve pluralization *slightly*, but we're not going to
maintain an actual mapping of every word as it's brittle, difficult to
maintain, and causes bug fixes to stop people's code from compiling.

Regardless of how good our inference is, we should decouple the table
name from the struct name. This now allows specifying the table name
with an annotation. This does not affect any public API, only
associations which I have not made public or documented as they're still
very prototypical.

It should be noted that this *only* affects other annotations on the
same struct. When we're processing an annotation on `Foo`, we don't
actually have a way to go look at the annotations on `Bar` (at least not
as far as I can tell). At this point in time, we do not directly
reference any struct in a way that should be affected by this.
`#[belongs_to]` comes close, but the table name is based on the
association name, not the foreign struct that we look for.

diesel_codegen/src/attr.rs

@@ -1,8 +1,8 @@
 use syntax::ast;
-use syntax::attr::AttrMetaMethods;
 use syntax::ext::base::ExtCtxt;
 use syntax::ptr::P;
-use syntax::parse::token::str_to_ident;
+
+use util::str_value_of_attr_with_name;
 
 #[derive(Debug, PartialEq, Eq)]
 pub struct Attr {
@@ -14,19 +14,8 @@ pub struct Attr {
 impl Attr {
     pub fn from_struct_field(cx: &mut ExtCtxt, field: &ast::StructField) -> Option<Self> {
         let field_name = field.node.ident();
-        let column_name = field.node.attrs.iter().filter_map(|attr| {
-            if attr.check_name("column_name") {
-                attr.value_str().map(|name| {
-                    str_to_ident(&name)
-                }).or_else(|| {
-                    cx.span_err(attr.span(),
-                        r#"`column_name` must be in the form `#[column_name="something"]`"#);
-                    None
-                })
-            } else {
-                None
-            }
-        }).nth(0);
+        let column_name =
+            str_value_of_attr_with_name(cx, &field.node.attrs, "column_name");
         let ty = field.node.ty.clone();
 
         match (column_name, field_name) {

diesel_codegen/src/lib.rs

@@ -24,6 +24,8 @@ include!(concat!(env!("OUT_DIR"), "/lib.rs"));
 #[cfg(not(feature = "with-syntex"))]
 include!("lib.in.rs");
 
+mod util;
+
 #[cfg(feature = "with-syntex")]
 pub fn register(reg: &mut syntex::Registry) {
     reg.add_attr("feature(custom_derive)");

diesel_codegen/src/model.rs

@@ -5,11 +5,13 @@ use syntax::ptr::P;
 use syntax::parse::token::str_to_ident;
 
 use attr::Attr;
+use util::str_value_of_attr_with_name;
 
 pub struct Model {
     pub ty: P<ast::Ty>,
     pub attrs: Vec<Attr>,
     pub name: ast::Ident,
+    table_name_from_annotation: Option<ast::Ident>,
 }
 
 impl Model {
@@ -19,6 +21,8 @@ impl Model {
         annotatable: &Annotatable,
     ) -> Option<Self> {
         if let Annotatable::Item(ref item) = *annotatable {
+            let table_name_from_annotation =
+                str_value_of_attr_with_name(cx, &item.attrs, "table_name");
             Attr::from_item(cx, item).map(|(generics, attrs)| {
                 let ty = builder.ty().path()
                     .segment(item.ident).with_generics(generics.clone())
@@ -27,6 +31,7 @@ impl Model {
                     ty: ty,
                     attrs: attrs,
                     name: item.ident,
+                    table_name_from_annotation: table_name_from_annotation,
                 }
             })
         } else {
@@ -39,8 +44,10 @@ impl Model {
     }
 
     pub fn table_name(&self) -> ast::Ident {
-        let pluralized = format!("{}s", self.name.name.as_str());
-        str_to_ident(&pluralized.to_lowercase())
+        self.table_name_from_annotation.unwrap_or_else(|| {
+            let pluralized = format!("{}s", self.name.name.as_str());
+            str_to_ident(&pluralized.to_lowercase())
+        })
     }
 
     pub fn attr_named(&self, name: ast::Ident) -> &Attr {

diesel_codegen/src/util.rs

@@ -0,0 +1,28 @@
+use syntax::ast;
+use syntax::attr::AttrMetaMethods;
+use syntax::ext::base::ExtCtxt;
+use syntax::parse::token::str_to_ident;
+
+fn str_value_of_attr(
+    cx: &mut ExtCtxt,
+    attr: &ast::Attribute,
+    name: &str,
+) -> Option<ast::Ident> {
+    attr.value_str().map(|value| {
+        str_to_ident(&value)
+    }).or_else(|| {
+        cx.span_err(attr.span(),
+            &format!(r#"`{}` must be in the form `#[{}="something"]`"#, name, name));
+        None
+    })
+}
+
+pub fn str_value_of_attr_with_name(
+    cx: &mut ExtCtxt,
+    attrs: &[ast::Attribute],
+    name: &str,
+) -> Option<ast::Ident> {
+    attrs.iter()
+        .find(|a| a.check_name(name))
+        .and_then(|a| str_value_of_attr(cx, &a, name))
+}

diesel_tests/tests/associations.rs

@@ -24,3 +24,18 @@ fn one_to_many_returns_query_source_for_association() {
     let found_posts: Vec<_> = Post::belonging_to(&tess).load(&connection).unwrap().collect();
     assert_eq!(tess_posts, found_posts);
 }
+
+#[test]
+fn association_where_struct_name_doesnt_match_table_name() {
+    let connection = connection_with_sean_and_tess_in_users_table();
+
+    let sean = find_user_by_name("Sean", &connection);
+    let post: Post = insert(&sean.new_post("Hello", None)).into(posts::table)
+        .get_result(&connection).unwrap();
+    insert(&NewComment(post.id, "comment")).into(comments::table)
+        .execute(&connection).unwrap();
+
+    let comment_text = SpecialComment::belonging_to(&post).select(comments::text)
+        .first::<String>(&connection);
+    assert_eq!(Ok("comment".into()), comment_text);
+}

diesel_tests/tests/schema.rs

@@ -59,6 +59,14 @@ pub struct Comment {
     text: String,
 }
 
+#[derive(PartialEq, Eq, Debug, Clone, Queriable)]
+#[belongs_to(post)]
+#[table_name="comments"]
+pub struct SpecialComment {
+    id: i32,
+    post_id: i32,
+}
+
 infer_schema!(dotenv!("DATABASE_URL"));
 numeric_expr!(users::id);