[Pending RFC] Const functions and inherent methods.

src/librustc/diagnostics.rs

@@ -67,6 +67,7 @@ register_diagnostics! {
     E0018,
     E0019,
     E0020,
+    E0021,
     E0022,
     E0109,
     E0110,

src/librustc/metadata/common.rs

@@ -256,3 +256,5 @@ pub const tag_codemap_filemap: uint = 0xa2;
 pub const tag_item_super_predicates: uint = 0xa3;
 
 pub const tag_defaulted_trait: uint = 0xa4;
+
+pub const tag_items_data_item_constness: uint = 0xa5;

src/librustc/metadata/csearch.rs

@@ -377,6 +377,11 @@ pub fn is_typedef(cstore: &cstore::CStore, did: ast::DefId) -> bool {
     decoder::is_typedef(&*cdata, did.node)
 }
 
+pub fn is_const_fn(cstore: &cstore::CStore, did: ast::DefId) -> bool {
+    let cdata = cstore.get_crate_data(did.krate);
+    decoder::is_const_fn(&*cdata, did.node)
+}
+
 pub fn get_stability(cstore: &cstore::CStore,
                      def: ast::DefId)
                      -> Option<attr::Stability> {

src/librustc/metadata/decoder.rs

@@ -176,6 +176,19 @@ fn item_visibility(item: rbml::Doc) -> ast::Visibility {
     }
 }
 
+fn fn_constness(item: rbml::Doc) -> ast::Constness {
+    match reader::maybe_get_doc(item, tag_items_data_item_constness) {
+        None => ast::Constness::NotConst,
+        Some(constness_doc) => {
+            match reader::doc_as_u8(constness_doc) as char {
+                'c' => ast::Constness::Const,
+                'n' => ast::Constness::NotConst,
+                _ => panic!("unknown constness character")
+            }
+        }
+    }
+}
+
 fn item_sort(item: rbml::Doc) -> Option<char> {
     let mut ret = None;
     reader::tagged_docs(item, tag_item_trait_item_sort, |doc| {
@@ -1451,6 +1464,14 @@ pub fn is_typedef(cdata: Cmd, id: ast::NodeId) -> bool {
     }
 }
 
+pub fn is_const_fn(cdata: Cmd, id: ast::NodeId) -> bool {
+    let item_doc = lookup_item(id, cdata.data());
+    match fn_constness(item_doc) {
+        ast::Constness::Const => true,
+        ast::Constness::NotConst => false,
+    }
+}
+
 fn doc_generics<'tcx>(base_doc: rbml::Doc,
                       tcx: &ty::ctxt<'tcx>,
                       cdata: Cmd,

src/librustc/metadata/encoder.rs

@@ -581,6 +581,16 @@ fn encode_visibility(rbml_w: &mut Encoder, visibility: ast::Visibility) {
     rbml_w.wr_tagged_u8(tag_items_data_item_visibility, ch as u8);
 }
 
+fn encode_constness(rbml_w: &mut Encoder, constness: ast::Constness) {
+    rbml_w.start_tag(tag_items_data_item_constness);
+    let ch = match constness {
+        ast::Constness::Const => 'c',
+        ast::Constness::NotConst => 'n',
+    };
+    rbml_w.wr_str(&ch.to_string());
+    rbml_w.end_tag();
+}
+
 fn encode_explicit_self(rbml_w: &mut Encoder,
                         explicit_self: &ty::ExplicitSelfCategory) {
     let tag = tag_item_trait_method_explicit_self;
@@ -831,10 +841,14 @@ fn encode_info_for_method<'a, 'tcx>(ecx: &EncodeContext<'a, 'tcx>,
             encode_attributes(rbml_w, &impl_item.attrs);
             let scheme = ty::lookup_item_type(ecx.tcx, m.def_id);
             let any_types = !scheme.generics.types.is_empty();
-            if any_types || is_default_impl || attr::requests_inline(&impl_item.attrs) {
+            let needs_inline = any_types || is_default_impl ||
+                               attr::requests_inline(&impl_item.attrs);
+            let constness = ast_method.pe_constness();
+            if needs_inline || constness == ast::Constness::Const {
                 encode_inlined_item(ecx, rbml_w, IIImplItemRef(local_def(parent_id),
                                                                impl_item));
             }
+            encode_constness(rbml_w, constness);
             if !any_types {
                 encode_symbol(ecx, rbml_w, m.def_id.node);
             }
@@ -1015,7 +1029,7 @@ fn encode_info_for_item(ecx: &EncodeContext,
         encode_stability(rbml_w, stab);
         rbml_w.end_tag();
       }
-      ast::ItemFn(ref decl, _, _, ref generics, _) => {
+      ast::ItemFn(ref decl, _, constness, _, ref generics, _) => {
         add_to_index(item, rbml_w, index);
         rbml_w.start_tag(tag_items_data_item);
         encode_def_id(rbml_w, def_id);
@@ -1025,12 +1039,14 @@ fn encode_info_for_item(ecx: &EncodeContext,
         encode_name(rbml_w, item.ident.name);
         encode_path(rbml_w, path);
         encode_attributes(rbml_w, &item.attrs);
-        if tps_len > 0 || attr::requests_inline(&item.attrs) {
+        let needs_inline = tps_len > 0 || attr::requests_inline(&item.attrs);
+        if needs_inline || constness == ast::Constness::Const {
             encode_inlined_item(ecx, rbml_w, IIItemRef(item));
         }
         if tps_len == 0 {
             encode_symbol(ecx, rbml_w, item.id);
         }
+        encode_constness(rbml_w, constness);
         encode_visibility(rbml_w, vis);
         encode_stability(rbml_w, stab);
         encode_method_argument_names(rbml_w, &**decl);
@@ -1875,7 +1891,7 @@ fn encode_reachable_extern_fns(ecx: &EncodeContext, rbml_w: &mut Encoder) {
 
     for id in ecx.reachable {
         if let Some(ast_map::NodeItem(i)) = ecx.tcx.map.find(*id) {
-            if let ast::ItemFn(_, _, abi, ref generics, _) = i.node {
+            if let ast::ItemFn(_, _, _, abi, ref generics, _) = i.node {
                 if abi != abi::Rust && !generics.is_type_parameterized() {
                     rbml_w.wr_tagged_u32(tag_reachable_extern_fn_id, *id);
                 }