codemap: Add utilities for looking up line ranges of spans

This commit adds extension methods to `Codemap` to allow looking up line
ranges for spans.

Refs #434

src/codemap.rs

@@ -1,13 +1,37 @@
-use syntax::codemap::{BytePos, CodeMap, Span};
+use std::rc::Rc;
+
+use syntax::codemap::{BytePos, CodeMap, FileMap, Span};
 
 use comment::FindUncommented;
 
+/// A range of lines in a file, inclusive of both ends.
+pub struct LineRange {
+    pub file: Rc<FileMap>,
+    pub lo: usize,
+    pub hi: usize,
+}
+
+impl LineRange {
+    pub fn file_name(&self) -> &str {
+        self.file.as_ref().name.as_str()
+    }
+}
+
 pub trait SpanUtils {
     fn span_after(&self, original: Span, needle: &str) -> BytePos;
     fn span_after_last(&self, original: Span, needle: &str) -> BytePos;
     fn span_before(&self, original: Span, needle: &str) -> BytePos;
 }
 
+pub trait LineRangeUtils {
+    /// Returns the `LineRange` that corresponds to `span` in `self`.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `span` crosses a file boundary, which shouldn't happen.
+    fn lookup_line_range(&self, span: Span) -> LineRange;
+}
+
 impl SpanUtils for CodeMap {
     #[inline]
     fn span_after(&self, original: Span, needle: &str) -> BytePos {
@@ -37,3 +61,21 @@ impl SpanUtils for CodeMap {
         original.lo + BytePos(offset as u32)
     }
 }
+
+impl LineRangeUtils for CodeMap {
+    fn lookup_line_range(&self, span: Span) -> LineRange {
+        let lo = self.lookup_char_pos(span.lo);
+        let hi = self.lookup_char_pos(span.hi);
+
+        assert!(lo.file.name == hi.file.name,
+                "span crossed file boundary: lo: {:?}, hi: {:?}",
+                lo,
+                hi);
+
+        LineRange {
+            file: lo.file.clone(),
+            lo: lo.line,
+            hi: hi.line,
+        }
+    }
+}