Make various fixes:

- add feature gate
- add basic tests
- adjust parser to eliminate conflict between `const fn` and associated
constants
- allow `const fn` in traits/trait-impls, but forbid later in type check
- correct some merge conflicts

Author: nikomatsakis

src/librustc/diagnostics.rs

@@ -846,5 +846,6 @@ register_diagnostics! {
     E0314, // closure outlives stack frame
     E0315, // cannot invoke closure outside of its lifetime
     E0316, // nested quantification of lifetimes
-    E0370  // discriminant overflow
+    E0370, // discriminant overflow
+    E0378  // method calls limited to constant inherent methods
 }

src/librustc/lib.rs

@@ -8,6 +8,10 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+// TODO list:
+// 1. Check that const fns cannot be defined in a trait or trait impl.
+//    (This used to be enforced in the parser.) Make sure there are test cases.
+
 //! The Rust compiler.
 //!
 //! # Note

src/librustc/metadata/encoder.rs

@@ -879,12 +879,11 @@ fn encode_info_for_method<'a, 'tcx>(ecx: &EncodeContext<'a, 'tcx>,
             let any_types = !scheme.generics.types.is_empty();
             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 {
+            if needs_inline || sig.constness == ast::Constness::Const {
                 encode_inlined_item(ecx, rbml_w, IIImplItemRef(local_def(parent_id),
                                                                impl_item));
             }
-            encode_constness(rbml_w, constness);
+            encode_constness(rbml_w, sig.constness);
             if !any_types {
                 encode_symbol(ecx, rbml_w, m.def_id.node);
             }

src/librustc/middle/check_const.rs

@@ -35,7 +35,6 @@ use util::nodemap::NodeMap;
 use util::ppaux;
 
 use syntax::ast;
-use syntax::ast_util::PostExpansionMethod;
 use syntax::codemap::Span;
 use syntax::print::pprust;
 use syntax::visit::{self, Visitor};
@@ -149,16 +148,16 @@ impl<'a, 'tcx> CheckCrateVisitor<'a, 'tcx> {
             Entry::Occupied(entry) => return *entry.get(),
             Entry::Vacant(entry) => {
                 // Prevent infinite recursion on re-entry.
-                entry.insert(PURE_CONST);
+                entry.insert(ConstQualif::empty());
             }
         }
 
         let mode = match fk {
-            visit::FkItemFn(_, _, _, ast::Constness::Const, _) => {
+            visit::FkItemFn(_, _, _, ast::Constness::Const, _, _) => {
                 Mode::ConstFn
             }
-            visit::FkMethod(_, _, m) => {
-                if m.pe_constness() == ast::Constness::Const {
+            visit::FkMethod(_, m, _) => {
+                if m.constness == ast::Constness::Const {
                     Mode::ConstFn
                 } else {
                     Mode::Var
@@ -189,7 +188,7 @@ impl<'a, 'tcx> CheckCrateVisitor<'a, 'tcx> {
 
         // Keep only bits that aren't affected by function body (NON_ZERO_SIZED),
         // and bits that don't change semantics, just optimizations (PREFER_IN_PLACE).
-        let qualif = qualif & (NON_ZERO_SIZED | PREFER_IN_PLACE);
+        let qualif = qualif & (ConstQualif::NON_ZERO_SIZED | ConstQualif::PREFER_IN_PLACE);
 
         self.tcx.const_qualif_map.borrow_mut().insert(fn_id, qualif);
         qualif
@@ -210,7 +209,7 @@ impl<'a, 'tcx> CheckCrateVisitor<'a, 'tcx> {
             self.add_qualif(qualif);
 
             if ty::type_contents(self.tcx, ret_ty).interior_unsafe() {
-                self.add_qualif(MUTABLE_MEM);
+                self.add_qualif(ConstQualif::MUTABLE_MEM);
             }
 
             true
@@ -366,7 +365,7 @@ impl<'a, 'tcx, 'v> Visitor<'v> for CheckCrateVisitor<'a, 'tcx> {
                                                        macro in const?!")
                 }
             };
-            self.add_qualif(NOT_CONST);
+            self.add_qualif(ConstQualif::NOT_CONST);
             if self.mode != Mode::Var {
                 span_err!(self.tcx.sess, span, E0016,
                           "blocks in {}s are limited to items and \
@@ -611,7 +610,7 @@ fn check_expr<'a, 'tcx>(v: &mut CheckCrateVisitor<'a, 'tcx>,
                 }
                 Some(def::DefLocal(_)) if v.mode == Mode::ConstFn => {
                     // Sadly, we can't determine whether the types are zero-sized.
-                    v.add_qualif(NOT_CONST | NON_ZERO_SIZED);
+                    v.add_qualif(ConstQualif::NOT_CONST | ConstQualif::NON_ZERO_SIZED);
                 }
                 def => {
                     v.add_qualif(ConstQualif::NOT_CONST);
@@ -660,20 +659,8 @@ fn check_expr<'a, 'tcx>(v: &mut CheckCrateVisitor<'a, 'tcx>,
                 }
             }
         }
-        ast::ExprBlock(ref block) => {
-            // Check all statements in the block
-            let mut block_span_err = |span| {
-                v.add_qualif(ConstQualif::NOT_CONST);
-                if v.mode != Mode::Var {
-                    span_err!(v.tcx.sess, e.span, E0015,
-                              "function calls in {}s are limited to \
-                               constant functions, \
-                               struct and enum constructors", v.msg());
-                }
-            }
-        }
         ast::ExprMethodCall(..) => {
-            let method_did = match v.tcx.method_map.borrow()[method_call].origin {
+            let method_did = match v.tcx.method_map.borrow()[&method_call].origin {
                 ty::MethodStatic(did) => Some(did),
                 _ => None
             };
@@ -682,9 +669,9 @@ fn check_expr<'a, 'tcx>(v: &mut CheckCrateVisitor<'a, 'tcx>,
                 None => false
             };
             if !is_const {
-                v.add_qualif(NOT_CONST);
+                v.add_qualif(ConstQualif::NOT_CONST);
                 if v.mode != Mode::Var {
-                    span_err!(v.tcx.sess, e.span, E0021,
+                    span_err!(v.tcx.sess, e.span, E0378,
                               "method calls in {}s are limited to \
                                constant inherent methods", v.msg());
                 }

src/librustc/middle/const_eval.rs

@@ -25,7 +25,7 @@ use util::ppaux::Repr;
 
 use syntax::ast::{self, Expr};
 use syntax::ast_map::blocks::FnLikeNode;
-use syntax::ast_util::{self, PostExpansionMethod};
+use syntax::ast_util;
 use syntax::codemap::Span;
 use syntax::feature_gate;
 use syntax::parse::token::InternedString;
@@ -216,17 +216,17 @@ fn inline_const_fn_from_external_crate(tcx: &ty::ctxt, def_id: ast::DefId)
     let fn_id = match csearch::maybe_get_item_ast(tcx, def_id,
         box |a, b, c, d| astencode::decode_inlined_item(a, b, c, d)) {
         csearch::FoundAst::Found(&ast::IIItem(ref item)) => Some(item.id),
-        csearch::FoundAst::Found(&ast::IIImplItem(_, ast::MethodImplItem(ref m))) => Some(m.id),
+        csearch::FoundAst::Found(&ast::IIImplItem(_, ref item)) => Some(item.id),
         _ => None
     };
     tcx.extern_const_fns.borrow_mut().insert(def_id,
                                              fn_id.unwrap_or(ast::DUMMY_NODE_ID));
     fn_id
 }
 
-pub fn lookup_const_fn_by_id<'a>(tcx: &'a ty::ctxt, def_id: ast::DefId)
-                                 -> Option<FnLikeNode<'a>> {
-
+pub fn lookup_const_fn_by_id<'tcx>(tcx: &ty::ctxt<'tcx>, def_id: ast::DefId)
+                                   -> Option<FnLikeNode<'tcx>>
+{
     let fn_id = if !ast_util::is_local(def_id) {
         if let Some(fn_id) = inline_const_fn_from_external_crate(tcx, def_id) {
             fn_id
@@ -243,11 +243,11 @@ pub fn lookup_const_fn_by_id<'a>(tcx: &'a ty::ctxt, def_id: ast::DefId)
     };
 
     match fn_like.kind() {
-        visit::FkItemFn(_, _, _, ast::Constness::Const, _) => {
+        visit::FkItemFn(_, _, _, ast::Constness::Const, _, _) => {
             Some(fn_like)
         }
-        visit::FkMethod(_, _, m) => {
-            if m.pe_constness() == ast::Constness::Const {
+        visit::FkMethod(_, m, _) => {
+            if m.constness == ast::Constness::Const {
                 Some(fn_like)
             } else {
                 None

src/librustc/middle/effect.rs

@@ -87,7 +87,7 @@ impl<'a, 'tcx, 'v> Visitor<'v> for EffectCheckVisitor<'a, 'tcx> {
                 block: &'v ast::Block, span: Span, _: ast::NodeId) {
 
         let (is_item_fn, is_unsafe_fn) = match fn_kind {
-            visit::FkItemFn(_, _, unsafety, _, _) =>
+            visit::FkItemFn(_, _, unsafety, _, _, _) =>
                 (true, unsafety == ast::Unsafety::Unsafe),
             visit::FkMethod(_, sig, _) =>
                 (true, sig.unsafety == ast::Unsafety::Unsafe),

src/librustc/middle/resolve_lifetime.rs

@@ -447,7 +447,7 @@ impl<'a> LifetimeContext<'a> {
                    fb: &'b ast::Block,
                    _span: Span) {
         match fk {
-            visit::FkItemFn(_, generics, _, _, _) => {
+            visit::FkItemFn(_, generics, _, _, _, _) => {
                 visit::walk_fn_decl(self, fd);
                 self.visit_generics(generics);
             }

src/librustc/middle/stability.rs

@@ -23,7 +23,7 @@ use syntax::{attr, visit};
 use syntax::ast;
 use syntax::ast::{Attribute, Block, Crate, DefId, FnDecl, NodeId, Variant};
 use syntax::ast::{Item, Generics, StructField};
-use syntax::ast_util::{is_local, PostExpansionMethod};
+use syntax::ast_util::is_local;
 use syntax::attr::{Stability, AttrMetaMethods};
 use syntax::visit::{FnKind, Visitor};
 use syntax::feature_gate::emit_feature_err;

src/librustc_lint/builtin.rs

@@ -1324,7 +1324,7 @@ impl LintPass for UnsafeCode {
     fn check_fn(&mut self, cx: &Context, fk: visit::FnKind, _: &ast::FnDecl,
                 _: &ast::Block, span: Span, _: ast::NodeId) {
         match fk {
-            visit::FkItemFn(_, _, ast::Unsafety::Unsafe, _, _) =>
+            visit::FkItemFn(_, _, ast::Unsafety::Unsafe, _, _, _) =>
                 cx.span_lint(UNSAFE_CODE, span, "declaration of an `unsafe` function"),
 
             visit::FkMethod(_, sig, _) => {

src/librustc_resolve/lib.rs

@@ -245,7 +245,7 @@ impl<'a, 'v, 'tcx> Visitor<'v> for Resolver<'a, 'tcx> {
                 _: Span,
                 node_id: NodeId) {
         let rib_kind = match function_kind {
-            visit::FkItemFn(_, generics, _, _, _) => {
+            visit::FkItemFn(_, generics, _, _, _, _) => {
                 self.visit_generics(generics);
                 ItemRibKind
             }