diff --git a/src/librustc/hir/lowering.rs b/src/librustc/hir/lowering.rs
index df82fee80f23..6e98c57d1cd3 100644
--- a/src/librustc/hir/lowering.rs
+++ b/src/librustc/hir/lowering.rs
@@ -8,37 +8,37 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// Lowers the AST to the HIR.
-//
-// Since the AST and HIR are fairly similar, this is mostly a simple procedure,
-// much like a fold. Where lowering involves a bit more work things get more
-// interesting and there are some invariants you should know about. These mostly
-// concern spans and ids.
-//
-// Spans are assigned to AST nodes during parsing and then are modified during
-// expansion to indicate the origin of a node and the process it went through
-// being expanded. Ids are assigned to AST nodes just before lowering.
-//
-// For the simpler lowering steps, ids and spans should be preserved. Unlike
-// expansion we do not preserve the process of lowering in the spans, so spans
-// should not be modified here. When creating a new node (as opposed to
-// 'folding' an existing one), then you create a new id using `next_id()`.
-//
-// You must ensure that ids are unique. That means that you should only use the
-// id from an AST node in a single HIR node (you can assume that AST node ids
-// are unique). Every new node must have a unique id. Avoid cloning HIR nodes.
-// If you do, you must then set the new node's id to a fresh one.
-//
-// Spans are used for error messages and for tools to map semantics back to
-// source code. It is therefore not as important with spans as ids to be strict
-// about use (you can't break the compiler by screwing up a span). Obviously, a
-// HIR node can only have a single span. But multiple nodes can have the same
-// span and spans don't need to be kept in order, etc. Where code is preserved
-// by lowering, it should have the same span as in the AST. Where HIR nodes are
-// new it is probably best to give a span for the whole AST node being lowered.
-// All nodes should have real spans, don't use dummy spans. Tools are likely to
-// get confused if the spans from leaf AST nodes occur in multiple places
-// in the HIR, especially for multiple identifiers.
+//! Lowers the AST to the HIR.
+//!
+//! Since the AST and HIR are fairly similar, this is mostly a simple procedure,
+//! much like a fold. Where lowering involves a bit more work things get more
+//! interesting and there are some invariants you should know about. These mostly
+//! concern spans and ids.
+//!
+//! Spans are assigned to AST nodes during parsing and then are modified during
+//! expansion to indicate the origin of a node and the process it went through
+//! being expanded. Ids are assigned to AST nodes just before lowering.
+//!
+//! For the simpler lowering steps, ids and spans should be preserved. Unlike
+//! expansion we do not preserve the process of lowering in the spans, so spans
+//! should not be modified here. When creating a new node (as opposed to
+//! 'folding' an existing one), then you create a new id using `next_id()`.
+//!
+//! You must ensure that ids are unique. That means that you should only use the
+//! id from an AST node in a single HIR node (you can assume that AST node ids
+//! are unique). Every new node must have a unique id. Avoid cloning HIR nodes.
+//! If you do, you must then set the new node's id to a fresh one.
+//!
+//! Spans are used for error messages and for tools to map semantics back to
+//! source code. It is therefore not as important with spans as ids to be strict
+//! about use (you can't break the compiler by screwing up a span). Obviously, a
+//! HIR node can only have a single span. But multiple nodes can have the same
+//! span and spans don't need to be kept in order, etc. Where code is preserved
+//! by lowering, it should have the same span as in the AST. Where HIR nodes are
+//! new it is probably best to give a span for the whole AST node being lowered.
+//! All nodes should have real spans, don't use dummy spans. Tools are likely to
+//! get confused if the spans from leaf AST nodes occur in multiple places
+//! in the HIR, especially for multiple identifiers.
 
 use hir;
 use hir::map::{Definitions, DefKey, REGULAR_SPACE};
@@ -70,8 +70,10 @@ const HIR_ID_COUNTER_LOCKED: u32 = 0xFFFFFFFF;
 
 pub struct LoweringContext<'a> {
     crate_root: Option<&'static str>,
+    
     // Use to assign ids to hir nodes that do not directly correspond to an ast node
     sess: &'a Session,
+    
     // As we walk the AST we must keep track of the current 'parent' def id (in
     // the form of a DefIndex) so that if we create a new node which introduces
     // a definition, then we can properly create the def id.
@@ -102,14 +104,14 @@ pub struct LoweringContext<'a> {
 }
 
 pub trait Resolver {
-    // Resolve a hir path generated by the lowerer when expanding `for`, `if let`, etc.
+    /// Resolve a hir path generated by the lowerer when expanding `for`, `if let`, etc.
     fn resolve_hir_path(&mut self, path: &mut hir::Path, is_value: bool);
 
-    // Obtain the resolution for a node id
+    /// Obtain the resolution for a node id
     fn get_resolution(&mut self, id: NodeId) -> Option<PathResolution>;
 
-    // We must keep the set of definitions up to date as we add nodes that weren't in the AST.
-    // This should only return `None` during testing.
+    /// We must keep the set of definitions up to date as we add nodes that weren't in the AST.
+    /// This should only return `None` during testing.
     fn definitions(&mut self) -> &mut Definitions;
 }