Fix ICE on inner enum in missing docs lint.

This also simplifies the lint by not storing variant depth or the struct
def stack, because we no longer need them.

src/librustc_lint/builtin.rs

@@ -259,12 +259,6 @@ fn check_trait_item(&mut self, cx: &LateContext, item: &hir::TraitItem) {
 }
 
 pub struct MissingDoc {
-    /// Stack of IDs of struct definitions.
-    struct_def_stack: Vec<ast::NodeId>,
-
-    /// True if inside variant definition
-    in_variant: bool,
-
     /// Stack of whether #[doc(hidden)] is set
     /// at each level which has lint attributes.
     doc_hidden_stack: Vec<bool>,
@@ -276,8 +270,6 @@ pub struct MissingDoc {
 impl MissingDoc {
     pub fn new() -> MissingDoc {
         MissingDoc {
-            struct_def_stack: vec![],
-            in_variant: false,
             doc_hidden_stack: vec![false],
             private_traits: HashSet::new(),
         }
@@ -345,25 +337,6 @@ fn exit_lint_attrs(&mut self, _: &LateContext, _attrs: &[ast::Attribute]) {
         self.doc_hidden_stack.pop().expect("empty doc_hidden_stack");
     }
 
-    fn check_struct_def(&mut self,
-                        _: &LateContext,
-                        _: &hir::VariantData,
-                        _: ast::Name,
-                        _: &hir::Generics,
-                        item_id: ast::NodeId) {
-        self.struct_def_stack.push(item_id);
-    }
-
-    fn check_struct_def_post(&mut self,
-                             _: &LateContext,
-                             _: &hir::VariantData,
-                             _: ast::Name,
-                             _: &hir::Generics,
-                             item_id: ast::NodeId) {
-        let popped = self.struct_def_stack.pop().expect("empty struct_def_stack");
-        assert!(popped == item_id);
-    }
-
     fn check_crate(&mut self, cx: &LateContext, krate: &hir::Crate) {
         self.check_missing_docs_attrs(cx, None, &krate.attrs, krate.span, "crate");
     }
@@ -451,16 +424,11 @@ fn check_impl_item(&mut self, cx: &LateContext, impl_item: &hir::ImplItem) {
 
     fn check_struct_field(&mut self, cx: &LateContext, sf: &hir::StructField) {
         if !sf.is_positional() {
-            if sf.vis == hir::Public || self.in_variant {
-                let cur_struct_def = *self.struct_def_stack
-                    .last()
-                    .expect("empty struct_def_stack");
-                self.check_missing_docs_attrs(cx,
-                                              Some(cur_struct_def),
-                                              &sf.attrs,
-                                              sf.span,
-                                              "a struct field")
-            }
+            self.check_missing_docs_attrs(cx,
+                                          Some(sf.id),
+                                          &sf.attrs,
+                                          sf.span,
+                                          "a struct field")
         }
     }
 
@@ -470,13 +438,6 @@ fn check_variant(&mut self, cx: &LateContext, v: &hir::Variant, _: &hir::Generic
                                       &v.node.attrs,
                                       v.span,
                                       "a variant");
-        assert!(!self.in_variant);
-        self.in_variant = true;
-    }
-
-    fn check_variant_post(&mut self, _: &LateContext, _: &hir::Variant, _: &hir::Generics) {
-        assert!(self.in_variant);
-        self.in_variant = false;
     }
 }
 

src/test/compile-fail/issue-40350.rs

@@ -0,0 +1,24 @@
+// Copyright 2017 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.
+
+#![feature(rustc_attrs)]
+#![allow(warnings)]
+
+enum E {
+    A = {
+        enum F { B }
+        0
+    }
+}
+
+#[rustc_error]
+fn main() {}
+//~^ ERROR compilation successful
+