Separate static item recursion check into its own pass

This new pass is run before type checking so that recursive items
are detected beforehand.  This prevents going into an infinite
recursion during type checking when a recursive item is used in
an array type.

As a bonus, use `span_err` instead of `span_fatal` so multiple
errors can be reported.

Closes issue #17252

src/librustc/middle/check_static_recursion.rs

@@ -0,0 +1,109 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// This compiler pass detects static items that refer to themselves
+// recursively.
+
+use driver::session::Session;
+use middle::resolve;
+use middle::def::DefStatic;
+
+use syntax::ast::{Crate, Expr, ExprPath, Item, ItemStatic, NodeId};
+use syntax::{ast_util, ast_map};
+use syntax::visit::Visitor;
+use syntax::visit;
+
+struct CheckCrateVisitor<'a, 'ast: 'a> {
+    sess: &'a Session,
+    def_map: &'a resolve::DefMap,
+    ast_map: &'a ast_map::Map<'ast>
+}
+
+impl<'v, 'a, 'ast> Visitor<'v> for CheckCrateVisitor<'a, 'ast> {
+    fn visit_item(&mut self, i: &Item) {
+        check_item(self, i);
+    }
+}
+
+pub fn check_crate<'ast>(sess: &Session,
+                         krate: &Crate,
+                         def_map: &resolve::DefMap,
+                         ast_map: &ast_map::Map<'ast>) {
+    let mut visitor = CheckCrateVisitor {
+        sess: sess,
+        def_map: def_map,
+        ast_map: ast_map
+    };
+    visit::walk_crate(&mut visitor, krate);
+    sess.abort_if_errors();
+}
+
+fn check_item(v: &mut CheckCrateVisitor, it: &Item) {
+    match it.node {
+        ItemStatic(_, _, ref ex) => {
+            check_item_recursion(v.sess, v.ast_map, v.def_map, it);
+            visit::walk_expr(v, &**ex)
+        },
+        _ => visit::walk_item(v, it)
+    }
+}
+
+struct CheckItemRecursionVisitor<'a, 'ast: 'a> {
+    root_it: &'a Item,
+    sess: &'a Session,
+    ast_map: &'a ast_map::Map<'ast>,
+    def_map: &'a resolve::DefMap,
+    idstack: Vec<NodeId>
+}
+
+// Make sure a const item doesn't recursively refer to itself
+// FIXME: Should use the dependency graph when it's available (#1356)
+pub fn check_item_recursion<'a>(sess: &'a Session,
+                                ast_map: &'a ast_map::Map,
+                                def_map: &'a resolve::DefMap,
+                                it: &'a Item) {
+
+    let mut visitor = CheckItemRecursionVisitor {
+        root_it: it,
+        sess: sess,
+        ast_map: ast_map,
+        def_map: def_map,
+        idstack: Vec::new()
+    };
+    visitor.visit_item(it);
+}
+
+impl<'a, 'ast, 'v> Visitor<'v> for CheckItemRecursionVisitor<'a, 'ast> {
+    fn visit_item(&mut self, it: &Item) {
+        if self.idstack.iter().any(|x| x == &(it.id)) {
+            self.sess.span_err(self.root_it.span, "recursive constant");
+            return;
+        }
+        self.idstack.push(it.id);
+        visit::walk_item(self, it);
+        self.idstack.pop();
+    }
+
+    fn visit_expr(&mut self, e: &Expr) {
+        match e.node {
+            ExprPath(..) => {
+                match self.def_map.borrow().find(&e.id) {
+                    Some(&DefStatic(def_id, _)) if
+                            ast_util::is_local(def_id) => {
+                        self.visit_item(&*self.ast_map.expect_item(def_id.node));
+                    }
+                    _ => ()
+                }
+            },
+            _ => ()
+        }
+        visit::walk_expr(self, e);
+    }
+}