Allow inheritance between structs.

No subtyping, no interaction with traits. Partially addresses rust-lang#9912.

Author: nrc

src/doc/rust.md

@@ -1170,6 +1170,22 @@ struct Cookie;
 let c = [Cookie, Cookie, Cookie, Cookie];
 ~~~~
 
+By using the `struct_inherit` feature gate, structures may use single inheritance. A Structure may only
+inherit from a single other structure, called the _super-struct_. The inheriting structure (sub-struct)
+acts as if all fields in the super-struct were present in the sub-struct. Fields declared in a sub-struct
+must not have the same name as any field in any (transitive) super-struct. All fields (both declared
+and inherited) must be specified in any initializers. Inheritance between structures does not give
+subtyping or coercion. The super-struct and sub-struct must be defined in the same crate. The super-struct
+must be declared using the `virtual` keyword.
+For example:
+
+~~~~ {.ignore}
+virtual struct Sup { x: int }
+struct Sub : Sup { y: int }
+let s = Sub {x: 10, y: 11};
+let sx = s.x;
+~~~~
+
 ### Enumerations
 
 An _enumeration_ is a simultaneous definition of a nominal [enumerated type](#enumerated-types) as well as a set of *constructors*,

src/librustc/front/config.rs

@@ -151,6 +151,8 @@ fn fold_struct(cx: &Context, def: &ast::StructDef) -> @ast::StructDef {
     @ast::StructDef {
         fields: fields.collect(),
         ctor_id: def.ctor_id,
+        super_struct: def.super_struct.clone(),
+        is_virtual: def.is_virtual,
     }
 }
 

src/librustc/front/feature_gate.rs

@@ -53,6 +53,7 @@ static KNOWN_FEATURES: &'static [(&'static str, Status)] = &[
     ("default_type_params", Active),
     ("quote", Active),
     ("linkage", Active),
+    ("struct_inherit", Active),
 
     // These are used to test this portion of the compiler, they don't actually
     // mean anything
@@ -188,11 +189,22 @@ impl<'a> Visitor<()> for Context<'a> {
                 }
             }
 
-            ast::ItemStruct(..) => {
+            ast::ItemStruct(struct_definition, _) => {
                 if attr::contains_name(i.attrs.as_slice(), "simd") {
                     self.gate_feature("simd", i.span,
                                       "SIMD types are experimental and possibly buggy");
                 }
+                match struct_definition.super_struct {
+                    Some(ref path) => self.gate_feature("struct_inherit", path.span,
+                                                        "struct inheritance is experimental \
+                                                         and possibly buggy"),
+                    None => {}
+                }
+                if struct_definition.is_virtual {
+                    self.gate_feature("struct_inherit", i.span,
+                                      "struct inheritance (`virtual` keyword) is \
+                                       experimental and possibly buggy");
+                }
             }
 
             _ => {}

src/librustc/metadata/common.rs

@@ -92,6 +92,7 @@ pub static tag_path_len: uint = 0x25;
 pub static tag_path_elem_mod: uint = 0x26;
 pub static tag_path_elem_name: uint = 0x27;
 pub static tag_item_field: uint = 0x28;
+pub static tag_item_field_origin: uint = 0x29;
 
 pub static tag_item_variances: uint = 0x2a;
 /*
@@ -102,43 +103,43 @@ pub static tag_item_variances: uint = 0x2a;
   both, tag_item_trait_method and tag_item_impl_method have to be two
   different tags.
  */
-pub static tag_item_impl_method: uint = 0x2c;
-pub static tag_item_trait_method_explicit_self: uint = 0x2d;
+pub static tag_item_impl_method: uint = 0x30;
+pub static tag_item_trait_method_explicit_self: uint = 0x31;
 
 
 // Reexports are found within module tags. Each reexport contains def_ids
 // and names.
-pub static tag_items_data_item_reexport: uint = 0x2f;
-pub static tag_items_data_item_reexport_def_id: uint = 0x30;
-pub static tag_items_data_item_reexport_name: uint = 0x31;
+pub static tag_items_data_item_reexport: uint = 0x38;
+pub static tag_items_data_item_reexport_def_id: uint = 0x39;
+pub static tag_items_data_item_reexport_name: uint = 0x3a;
 
 // used to encode crate_ctxt side tables
 #[deriving(Eq)]
 #[repr(uint)]
-pub enum astencode_tag { // Reserves 0x32 -- 0x45
-    tag_ast = 0x32,
-
-    tag_tree = 0x33,
-
-    tag_id_range = 0x34,
-
-    tag_table = 0x35,
-    tag_table_id = 0x36,
-    tag_table_val = 0x37,
-    tag_table_def = 0x38,
-    tag_table_node_type = 0x39,
-    tag_table_node_type_subst = 0x3a,
-    tag_table_freevars = 0x3b,
-    tag_table_tcache = 0x3c,
-    tag_table_param_defs = 0x3d,
-    tag_table_mutbl = 0x3e,
-    tag_table_last_use = 0x3f,
-    tag_table_spill = 0x40,
-    tag_table_method_map = 0x41,
-    tag_table_vtable_map = 0x42,
-    tag_table_adjustments = 0x43,
-    tag_table_moves_map = 0x44,
-    tag_table_capture_map = 0x45
+pub enum astencode_tag { // Reserves 0x40 -- 0x5f
+    tag_ast = 0x40,
+
+    tag_tree = 0x41,
+
+    tag_id_range = 0x42,
+
+    tag_table = 0x43,
+    tag_table_id = 0x44,
+    tag_table_val = 0x45,
+    tag_table_def = 0x46,
+    tag_table_node_type = 0x47,
+    tag_table_node_type_subst = 0x48,
+    tag_table_freevars = 0x49,
+    tag_table_tcache = 0x4a,
+    tag_table_param_defs = 0x4b,
+    tag_table_mutbl = 0x4c,
+    tag_table_last_use = 0x4d,
+    tag_table_spill = 0x4e,
+    tag_table_method_map = 0x4f,
+    tag_table_vtable_map = 0x50,
+    tag_table_adjustments = 0x51,
+    tag_table_moves_map = 0x52,
+    tag_table_capture_map = 0x53
 }
 static first_astencode_tag: uint = tag_ast as uint;
 static last_astencode_tag: uint = tag_table_capture_map as uint;
@@ -151,9 +152,9 @@ impl astencode_tag {
     }
 }
 
-pub static tag_item_trait_method_sort: uint = 0x46;
+pub static tag_item_trait_method_sort: uint = 0x60;
 
-pub static tag_item_impl_type_basename: uint = 0x47;
+pub static tag_item_impl_type_basename: uint = 0x61;
 
 // Language items are a top-level directory (for speed). Hierarchy:
 //
@@ -162,42 +163,42 @@ pub static tag_item_impl_type_basename: uint = 0x47;
 //   - tag_lang_items_item_id: u32
 //   - tag_lang_items_item_node_id: u32
 
-pub static tag_lang_items: uint = 0x48;
-pub static tag_lang_items_item: uint = 0x49;
-pub static tag_lang_items_item_id: uint = 0x4a;
-pub static tag_lang_items_item_node_id: uint = 0x4b;
+pub static tag_lang_items: uint = 0x70;
+pub static tag_lang_items_item: uint = 0x71;
+pub static tag_lang_items_item_id: uint = 0x72;
+pub static tag_lang_items_item_node_id: uint = 0x73;
 
-pub static tag_item_unnamed_field: uint = 0x4c;
-pub static tag_items_data_item_visibility: uint = 0x4e;
+pub static tag_item_unnamed_field: uint = 0x74;
+pub static tag_items_data_item_visibility: uint = 0x76;
 
-pub static tag_item_method_tps: uint = 0x51;
-pub static tag_item_method_fty: uint = 0x52;
+pub static tag_item_method_tps: uint = 0x79;
+pub static tag_item_method_fty: uint = 0x7a;
 
-pub static tag_mod_child: uint = 0x53;
-pub static tag_misc_info: uint = 0x54;
-pub static tag_misc_info_crate_items: uint = 0x55;
+pub static tag_mod_child: uint = 0x7b;
+pub static tag_misc_info: uint = 0x7c;
+pub static tag_misc_info_crate_items: uint = 0x7d;
 
-pub static tag_item_method_provided_source: uint = 0x56;
-pub static tag_item_impl_vtables: uint = 0x57;
+pub static tag_item_method_provided_source: uint = 0x7e;
+pub static tag_item_impl_vtables: uint = 0x7f;
 
-pub static tag_impls: uint = 0x58;
-pub static tag_impls_impl: uint = 0x59;
+pub static tag_impls: uint = 0x80;
+pub static tag_impls_impl: uint = 0x81;
 
-pub static tag_items_data_item_inherent_impl: uint = 0x5a;
-pub static tag_items_data_item_extension_impl: uint = 0x5b;
+pub static tag_items_data_item_inherent_impl: uint = 0x82;
+pub static tag_items_data_item_extension_impl: uint = 0x83;
 
-pub static tag_region_param_def: uint = 0x5c;
-pub static tag_region_param_def_ident: uint = 0x5d;
-pub static tag_region_param_def_def_id: uint = 0x5e;
+pub static tag_region_param_def: uint = 0x84;
+pub static tag_region_param_def_ident: uint = 0x85;
+pub static tag_region_param_def_def_id: uint = 0x86;
 
-pub static tag_native_libraries: uint = 0x5f;
-pub static tag_native_libraries_lib: uint = 0x60;
-pub static tag_native_libraries_name: uint = 0x61;
-pub static tag_native_libraries_kind: uint = 0x62;
+pub static tag_native_libraries: uint = 0x87;
+pub static tag_native_libraries_lib: uint = 0x88;
+pub static tag_native_libraries_name: uint = 0x89;
+pub static tag_native_libraries_kind: uint = 0x8a;
 
-pub static tag_macro_registrar_fn: uint = 0x63;
-pub static tag_exported_macros: uint = 0x64;
-pub static tag_macro_def: uint = 0x65;
+pub static tag_macro_registrar_fn: uint = 0x8b;
+pub static tag_exported_macros: uint = 0x8c;
+pub static tag_macro_def: uint = 0x8d;
 
 #[deriving(Clone, Show)]
 pub struct LinkMeta {

src/librustc/metadata/decoder.rs

@@ -976,21 +976,27 @@ pub fn get_struct_fields(intr: Rc<IdentInterner>, cdata: Cmd, id: ast::NodeId)
             // FIXME #6993: name should be of type Name, not Ident
             let name = item_name(&*intr, an_item);
             let did = item_def_id(an_item, cdata);
+            let tagdoc = reader::get_doc(an_item, tag_item_field_origin);
+            let origin_id =  translate_def_id(cdata, reader::with_doc_data(tagdoc, parse_def_id));
             result.push(ty::field_ty {
                 name: name.name,
-                id: did, vis:
-                struct_field_family_to_visibility(f),
+                id: did,
+                vis: struct_field_family_to_visibility(f),
+                origin: origin_id,
             });
         }
         true
     });
     reader::tagged_docs(item, tag_item_unnamed_field, |an_item| {
         let did = item_def_id(an_item, cdata);
+        let tagdoc = reader::get_doc(an_item, tag_item_field_origin);
         let f = item_family(an_item);
+        let origin_id =  translate_def_id(cdata, reader::with_doc_data(tagdoc, parse_def_id));
         result.push(ty::field_ty {
             name: special_idents::unnamed_field.name,
             id: did,
             vis: struct_field_family_to_visibility(f),
+            origin: origin_id,
         });
         true
     });

src/librustc/metadata/encoder.rs

@@ -302,23 +302,22 @@ fn encode_parent_item(ebml_w: &mut Encoder, id: DefId) {
 }
 
 fn encode_struct_fields(ebml_w: &mut Encoder,
-                        def: @StructDef) {
-    for f in def.fields.iter() {
-        match f.node.kind {
-            NamedField(ident, vis) => {
-               ebml_w.start_tag(tag_item_field);
-               encode_struct_field_family(ebml_w, vis);
-               encode_name(ebml_w, ident.name);
-               encode_def_id(ebml_w, local_def(f.node.id));
-               ebml_w.end_tag();
-            }
-            UnnamedField(vis) => {
-                ebml_w.start_tag(tag_item_unnamed_field);
-                encode_struct_field_family(ebml_w, vis);
-                encode_def_id(ebml_w, local_def(f.node.id));
-                ebml_w.end_tag();
-            }
+                        fields: &Vec<ty::field_ty>,
+                        origin: DefId) {
+    for f in fields.iter() {
+        if f.name == special_idents::unnamed_field.name {
+            ebml_w.start_tag(tag_item_unnamed_field);
+        } else {
+            ebml_w.start_tag(tag_item_field);
+            encode_name(ebml_w, f.name);
         }
+        encode_struct_field_family(ebml_w, f.vis);
+        encode_def_id(ebml_w, f.id);
+        ebml_w.start_tag(tag_item_field_origin);
+        let s = def_to_str(origin);
+        ebml_w.writer.write(s.as_bytes());
+        ebml_w.end_tag();
+        ebml_w.end_tag();
     }
 }
 
@@ -356,12 +355,13 @@ fn encode_enum_variant_info(ecx: &EncodeContext,
                 encode_symbol(ecx, ebml_w, variant.node.id);
             }
             ast::TupleVariantKind(_) => {},
-            ast::StructVariantKind(def) => {
+            ast::StructVariantKind(_) => {
+                let fields = ty::lookup_struct_fields(ecx.tcx, def_id);
                 let idx = encode_info_for_struct(ecx,
                                                  ebml_w,
-                                                 def.fields.as_slice(),
+                                                 &fields,
                                                  index);
-                encode_struct_fields(ebml_w, def);
+                encode_struct_fields(ebml_w, &fields, def_id);
                 let bkts = create_index(idx);
                 encode_index(ebml_w, bkts, write_i64);
             }
@@ -680,7 +680,7 @@ fn encode_provided_source(ebml_w: &mut Encoder,
 /* Returns an index of items in this class */
 fn encode_info_for_struct(ecx: &EncodeContext,
                           ebml_w: &mut Encoder,
-                          fields: &[StructField],
+                          fields: &Vec<ty::field_ty>,
                           global_index: @RefCell<Vec<entry<i64>> >)
                           -> Vec<entry<i64>> {
     /* Each class has its own index, since different classes
@@ -690,22 +690,19 @@ fn encode_info_for_struct(ecx: &EncodeContext,
      /* We encode both private and public fields -- need to include
         private fields to get the offsets right */
     for field in fields.iter() {
-        let (nm, vis) = match field.node.kind {
-            NamedField(nm, vis) => (nm, vis),
-            UnnamedField(vis) => (special_idents::unnamed_field, vis)
-        };
+        let nm = field.name;
+        let id = field.id.node;
 
-        let id = field.node.id;
         index.push(entry {val: id as i64, pos: ebml_w.writer.tell().unwrap()});
         global_index.borrow_mut().push(entry {
             val: id as i64,
             pos: ebml_w.writer.tell().unwrap(),
         });
         ebml_w.start_tag(tag_items_data_item);
         debug!("encode_info_for_struct: doing {} {}",
-               token::get_ident(nm), id);
-        encode_struct_field_family(ebml_w, vis);
-        encode_name(ebml_w, nm.name);
+               token::get_name(nm), id);
+        encode_struct_field_family(ebml_w, field.vis);
+        encode_name(ebml_w, nm);
         encode_type(ecx, ebml_w, node_id_to_type(tcx, id));
         encode_def_id(ebml_w, local_def(id));
         ebml_w.end_tag();
@@ -997,12 +994,16 @@ fn encode_info_for_item(ecx: &EncodeContext,
                                  generics);
       }
       ItemStruct(struct_def, _) => {
+        let fields = ty::lookup_struct_fields(tcx, def_id);
+
         /* First, encode the fields
            These come first because we need to write them to make
            the index, and the index needs to be in the item for the
            class itself */
-        let idx = encode_info_for_struct(ecx, ebml_w,
-                                         struct_def.fields.as_slice(), index);
+        let idx = encode_info_for_struct(ecx,
+                                         ebml_w,
+                                         &fields,
+                                         index);
 
         /* Index the class*/
         add_to_index(item, ebml_w, index);
@@ -1022,7 +1023,7 @@ fn encode_info_for_item(ecx: &EncodeContext,
         /* Encode def_ids for each field and method
          for methods, write all the stuff get_trait_method
         needs to know*/
-        encode_struct_fields(ebml_w, struct_def);
+        encode_struct_fields(ebml_w, &fields, def_id);
 
         (ecx.encode_inlined_item)(ecx, ebml_w, IIItemRef(item));