Make sure all full-line spans are highlighted properly

Even if the context covers lines after the fully-covered line, the
span shouldn't point to them.

pkgs/source_span/lib/src/highlighter.dart

diff --git a/pkgs/source_span/lib/src/highlighter.dart b/pkgs/source_span/lib/src/highlighter.dart
index a05412a..97d696d 100644
--- a/pkgs/source_span/lib/src/highlighter.dart
+++ b/pkgs/source_span/lib/src/highlighter.dart
@@ -99,6 +99,22 @@
       newSpan = new SourceSpanWithContext(start, end, text, context);
     }
 
+    // Normalize [span] so that the end location is at the end of a line, rather
+    // than on the beginning of the next line.
+    if (newSpan.end.column == 0 && newSpan.end.line != newSpan.start.line) {
+      assert(newSpan.text.endsWith("\n"));
+
+      var text = newSpan.text.substring(0, newSpan.text.length - 1);
+      newSpan = new SourceSpanWithContext(
+          newSpan.start,
+          new SourceLocation(span.end.offset - 1,
+              sourceUrl: span.sourceUrl,
+              line: span.end.line - 1,
+              column: _lastColumn(text)),
+          text,
+          newSpan.context);
+    }
+
     return new Highlighter._(newSpan, color);
   }
 

pkgs/source_span/test/highlight_test.dart

diff --git a/pkgs/source_span/test/highlight_test.dart b/pkgs/source_span/test/highlight_test.dart
index 71b58c3..e2536ba 100644
--- a/pkgs/source_span/test/highlight_test.dart
+++ b/pkgs/source_span/test/highlight_test.dart
@@ -316,21 +316,57 @@
     });
   });
 
-  test("supports lines of preceding and following context", () {
-    var span = new SourceSpanWithContext(
-        new SourceLocation(5, line: 2, column: 5, sourceUrl: "foo.dart"),
-        new SourceLocation(12, line: 2, column: 12, sourceUrl: "foo.dart"),
-        "foo bar",
-        "previous\nlines\n-----foo bar-----\nfollowing line\n");
+  group("supports lines of preceding and following context for a span", () {
+    test("within a single line", () {
+      var span = new SourceSpanWithContext(
+          new SourceLocation(20, line: 2, column: 5, sourceUrl: "foo.dart"),
+          new SourceLocation(27, line: 2, column: 12, sourceUrl: "foo.dart"),
+          "foo bar",
+          "previous\nlines\n-----foo bar-----\nfollowing line\n");
 
-    expect(span.highlight(color: colors.YELLOW), equals("""
-${colors.BLUE}  ,${colors.NONE}
-${colors.BLUE}1 |${colors.NONE} previous
-${colors.BLUE}2 |${colors.NONE} lines
-${colors.BLUE}3 |${colors.NONE} -----${colors.YELLOW}foo bar${colors.NONE}-----
-${colors.BLUE}  |${colors.NONE}      ${colors.YELLOW}^^^^^^^${colors.NONE}
-${colors.BLUE}4 |${colors.NONE} following line
-${colors.BLUE}  '${colors.NONE}"""));
+      expect(span.highlight(), equals("""
+  ,
+1 | previous
+2 | lines
+3 | -----foo bar-----
+  |      ^^^^^^^
+4 | following line
+  '"""));
+    });
+
+    test("covering a full line", () {
+      var span = new SourceSpanWithContext(
+          new SourceLocation(15, line: 2, column: 0, sourceUrl: "foo.dart"),
+          new SourceLocation(33, line: 3, column: 0, sourceUrl: "foo.dart"),
+          "-----foo bar-----\n",
+          "previous\nlines\n-----foo bar-----\nfollowing line\n");
+
+      expect(span.highlight(), equals("""
+  ,
+1 | previous
+2 | lines
+3 | -----foo bar-----
+  | ^^^^^^^^^^^^^^^^^
+4 | following line
+  '"""));
+    });
+
+    test("covering multiple full lines", () {
+      var span = new SourceSpanWithContext(
+          new SourceLocation(15, line: 2, column: 0, sourceUrl: "foo.dart"),
+          new SourceLocation(23, line: 4, column: 0, sourceUrl: "foo.dart"),
+          "foo\nbar\n",
+          "previous\nlines\nfoo\nbar\nfollowing line\n");
+
+      expect(span.highlight(), equals("""
+  ,
+1 |   previous
+2 |   lines
+3 | / foo
+4 | \\ bar
+5 |   following line
+  '"""));
+    });
   });
 
   group("colors", () {