diff --git a/CHANGELOG.md b/CHANGELOG.md
index 014cc4c..c24535b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,5 @@
+# 1.6.1-dev
+
 # 1.6.0
 
 * Add support for highlighting multiple source spans at once, providing more
diff --git a/analysis_options.yaml b/analysis_options.yaml
index 0ce7911..ab5a4f2 100644
--- a/analysis_options.yaml
+++ b/analysis_options.yaml
@@ -2,9 +2,6 @@
 analyzer:
   strong-mode:
     implicit-casts: false
-  errors:
-    # TODO(natebosch): fix and re-enable.
-    prefer_single_quotes: ignore
 linter:
   rules:
   - always_declare_return_types
@@ -29,8 +26,7 @@
   - await_only_futures
   - camel_case_types
   - cancel_subscriptions
-  # TODO(natebosch): fix and re-enable.
-  #- cascade_invocations
+  - cascade_invocations
   - comment_references
   - constant_identifier_names
   - control_flow_in_finally
@@ -63,12 +59,10 @@
   - prefer_contains
   - prefer_equal_for_default_values
   - prefer_final_fields
-  # TODO(natebosch): fix and re-enable.
-  #- prefer_final_locals
+  - prefer_final_locals
   - prefer_generic_function_type_aliases
   - prefer_initializing_formals
-  # TODO(natebosch): fix and re-enable.
-  #- prefer_interpolation_to_compose_strings
+  - prefer_interpolation_to_compose_strings
   - prefer_is_empty
   - prefer_is_not_empty
   - prefer_null_aware_operators
diff --git a/lib/src/highlighter.dart b/lib/src/highlighter.dart
index feb5594..cef6f79 100644
--- a/lib/src/highlighter.dart
+++ b/lib/src/highlighter.dart
@@ -114,8 +114,8 @@
   /// file that aren't adjacent in the original file.
   static bool _contiguous(List<_Line> lines) {
     for (var i = 0; i < lines.length - 1; i++) {
-      var thisLine = lines[i];
-      var nextLine = lines[i + 1];
+      final thisLine = lines[i];
+      final nextLine = lines[i + 1];
       if (thisLine.number + 1 != nextLine.number &&
           thisLine.url == nextLine.url) {
         return false;
@@ -127,7 +127,7 @@
   /// Collect all the source lines from the contexts of all spans in
   /// [highlights], and associates them with the highlights that cover them.
   static List<_Line> _collateLines(List<_Highlight> highlights) {
-    var highlightsByUrl =
+    final highlightsByUrl =
         groupBy(highlights, (highlight) => highlight.span.sourceUrl);
     for (var list in highlightsByUrl.values) {
       list.sort((highlight1, highlight2) =>
@@ -137,19 +137,19 @@
     return highlightsByUrl.values.expand((highlightsForFile) {
       // First, create a list of all the lines in the current file that we have
       // context for along with their line numbers.
-      var lines = <_Line>[];
+      final lines = <_Line>[];
       for (var highlight in highlightsForFile) {
-        var context = highlight.span.context;
+        final context = highlight.span.context;
         // If [highlight.span.context] contains lines prior to the one
         // [highlight.span.text] appears on, write those first.
-        var lineStart = findLineStart(
+        final lineStart = findLineStart(
             context, highlight.span.text, highlight.span.start.column);
         assert(lineStart != null); // enforced by [_normalizeContext]
 
-        var linesBeforeSpan =
+        final linesBeforeSpan =
             '\n'.allMatches(context.substring(0, lineStart)).length;
 
-        var url = highlight.span.sourceUrl;
+        final url = highlight.span.sourceUrl;
         var lineNumber = highlight.span.start.line - linesBeforeSpan;
         for (var line in context.split('\n')) {
           // Only add a line if it hasn't already been added for a previous span.
@@ -161,14 +161,14 @@
       }
 
       // Next, associate each line with each highlights that covers it.
-      var activeHighlights = <_Highlight>[];
+      final activeHighlights = <_Highlight>[];
       var highlightIndex = 0;
       for (var line in lines) {
         activeHighlights.removeWhere((highlight) =>
             highlight.span.sourceUrl != line.url ||
             highlight.span.end.line < line.number);
 
-        var oldHighlightLength = activeHighlights.length;
+        final oldHighlightLength = activeHighlights.length;
         for (var highlight in highlightsForFile.skip(highlightIndex)) {
           if (highlight.span.start.line > line.number) break;
           if (highlight.span.sourceUrl != line.url) break;
@@ -192,12 +192,12 @@
     // Each index of this list represents a column after the sidebar that could
     // contain a line indicating an active highlight. If it's `null`, that
     // column is empty; if it contains a highlight, it should be drawn for that column.
-    var highlightsByColumn = List<_Highlight>(_maxMultilineSpans);
+    final highlightsByColumn = List<_Highlight>(_maxMultilineSpans);
 
     for (var i = 0; i < _lines.length; i++) {
-      var line = _lines[i];
+      final line = _lines[i];
       if (i > 0) {
-        var lastLine = _lines[i - 1];
+        final lastLine = _lines[i - 1];
         if (lastLine.url != line.url) {
           _writeSidebar(end: glyph.upEnd);
           _buffer.writeln();
@@ -226,7 +226,7 @@
       _writeMultilineHighlights(line, highlightsByColumn);
       if (highlightsByColumn.isNotEmpty) _buffer.write(' ');
 
-      var primary = line.highlights
+      final primary = line.highlights
           .firstWhere((highlight) => highlight.isPrimary, orElse: () => null);
       if (primary != null) {
         _writeHighlightedText(
@@ -263,9 +263,9 @@
       _writeSidebar(end: glyph.downEnd);
     } else {
       _writeSidebar(end: glyph.topLeftCorner);
-      _colorize(() => _buffer.write("${glyph.horizontalLine * 2}>"),
+      _colorize(() => _buffer.write('${glyph.horizontalLine * 2}>'),
           color: colors.blue);
-      _buffer.write(" ${p.prettyUri(url)}");
+      _buffer.write(' ${p.prettyUri(url)}');
     }
     _buffer.writeln();
   }
@@ -284,13 +284,13 @@
     var openedOnThisLine = false;
     String openedOnThisLineColor;
 
-    var currentColor = current == null
+    final currentColor = current == null
         ? null
         : current.isPrimary ? _primaryColor : _secondaryColor;
     var foundCurrent = false;
     for (var highlight in highlightsByColumn) {
-      var startLine = highlight?.span?.start?.line;
-      var endLine = highlight?.span?.end?.line;
+      final startLine = highlight?.span?.start?.line;
+      final endLine = highlight?.span?.end?.line;
       if (current != null && highlight == current) {
         foundCurrent = true;
         assert(startLine == line.number || endLine == line.number);
@@ -312,7 +312,7 @@
         }
       } else {
         _colorize(() {
-          var vertical = openedOnThisLine ? glyph.cross : glyph.verticalLine;
+          final vertical = openedOnThisLine ? glyph.cross : glyph.verticalLine;
           if (current != null) {
             _buffer.write(vertical);
           } else if (startLine == line.number) {
@@ -354,7 +354,7 @@
   /// This may either add or remove [highlight] from [highlightsByColumn].
   void _writeIndicator(
       _Line line, _Highlight highlight, List<_Highlight> highlightsByColumn) {
-    var color = highlight.isPrimary ? _primaryColor : _secondaryColor;
+    final color = highlight.isPrimary ? _primaryColor : _secondaryColor;
     if (!isMultiline(highlight.span)) {
       _writeSidebar();
       _buffer.write(' ');
@@ -363,7 +363,7 @@
 
       _colorize(() {
         _writeUnderline(line, highlight.span,
-            highlight.isPrimary ? "^" : glyph.horizontalLineBold);
+            highlight.isPrimary ? '^' : glyph.horizontalLineBold);
         _writeLabel(highlight.label);
       }, color: color);
       _buffer.writeln();
@@ -378,7 +378,7 @@
           color: color);
       _buffer.writeln();
     } else if (highlight.span.end.line == line.number) {
-      var coversWholeLine = highlight.span.end.column == line.text.length;
+      final coversWholeLine = highlight.span.end.column == line.text.length;
       if (coversWholeLine && highlight.label == null) {
         replaceWithNull(highlightsByColumn, highlight);
         return;
@@ -413,13 +413,14 @@
 
     // Adjust the start and end columns to account for any tabs that were
     // converted to spaces.
-    var tabsBefore = _countTabs(line.text.substring(0, startColumn));
-    var tabsInside = _countTabs(line.text.substring(startColumn, endColumn));
+    final tabsBefore = _countTabs(line.text.substring(0, startColumn));
+    final tabsInside = _countTabs(line.text.substring(startColumn, endColumn));
     startColumn += tabsBefore * (_spacesPerTab - 1);
     endColumn += (tabsBefore + tabsInside) * (_spacesPerTab - 1);
 
-    _buffer.write(" " * startColumn);
-    _buffer.write(character * math.max(endColumn - startColumn, 1));
+    _buffer
+      ..write(' ' * startColumn)
+      ..write(character * math.max(endColumn - startColumn, 1));
   }
 
   /// Write an arrow pointing to column [column] in [line].
@@ -427,15 +428,16 @@
   /// If the arrow points to a tab character, this will point to the beginning
   /// of the tab if [beginning] is `true` and the end if it's `false`.
   void _writeArrow(_Line line, int column, {bool beginning = true}) {
-    var tabs = _countTabs(line.text.substring(0, column + (beginning ? 0 : 1)));
+    final tabs =
+        _countTabs(line.text.substring(0, column + (beginning ? 0 : 1)));
     _buffer
       ..write(glyph.horizontalLine * (1 + column + tabs * (_spacesPerTab - 1)))
-      ..write("^");
+      ..write('^');
   }
 
   /// Writes a space followed by [label] if [label] isn't `null`.
   void _writeLabel(String label) {
-    if (label != null) _buffer.write(" $label");
+    if (label != null) _buffer.write(' $label');
   }
 
   /// Writes a snippet from the source text, converting hard tab characters into
@@ -462,8 +464,9 @@
     // human-friendly 1-indexed line numbers.
     if (line != null) text = (line + 1).toString();
     _colorize(() {
-      _buffer.write((text ?? '').padRight(_paddingBeforeSidebar));
-      _buffer.write(end ?? glyph.verticalLine);
+      _buffer
+        ..write((text ?? '').padRight(_paddingBeforeSidebar))
+        ..write(end ?? glyph.verticalLine);
     }, color: colors.blue);
   }
 
@@ -612,7 +615,7 @@
         text,
         // If the context also ends with a newline, it's possible that we don't
         // have the full context for that line, so we shouldn't print it at all.
-        span.context.endsWith("\n")
+        span.context.endsWith('\n')
             ? span.context.substring(0, span.context.length - 1)
             : span.context);
   }
@@ -640,11 +643,11 @@
 
   @override
   String toString() {
-    var buffer = StringBuffer();
-    if (isPrimary) buffer.write("primary ");
-    buffer.write("${span.start.line}:${span.start.column}-"
-        "${span.end.line}:${span.end.column}");
-    if (label != null) buffer.write(" ($label)");
+    final buffer = StringBuffer();
+    if (isPrimary) buffer.write('primary ');
+    buffer.write('${span.start.line}:${span.start.column}-'
+        '${span.end.line}:${span.end.column}');
+    if (label != null) buffer.write(' ($label)');
     return buffer.toString();
   }
 }
diff --git a/lib/src/span_exception.dart b/lib/src/span_exception.dart
index 5b33d06..32aaa4e 100644
--- a/lib/src/span_exception.dart
+++ b/lib/src/span_exception.dart
@@ -92,11 +92,12 @@
       useColor = true;
     }
 
-    return "Error on " +
-        span.messageMultiple(message, primaryLabel, secondarySpans,
-            color: useColor,
-            primaryColor: primaryColor,
-            secondaryColor: secondaryColor);
+    final formatted = span.messageMultiple(
+        message, primaryLabel, secondarySpans,
+        color: useColor,
+        primaryColor: primaryColor,
+        secondaryColor: secondaryColor);
+    return 'Error on $formatted';
   }
 }
 
diff --git a/lib/src/utils.dart b/lib/src/utils.dart
index 12b15b3..5cb5e90 100644
--- a/lib/src/utils.dart
+++ b/lib/src/utils.dart
@@ -35,16 +35,16 @@
 
 /// Sets the first `null` element of [list] to [element].
 void replaceFirstNull<E>(List<E> list, E element) {
-  var index = list.indexOf(null);
-  if (index < 0) throw ArgumentError("$list contains no null elements.");
+  final index = list.indexOf(null);
+  if (index < 0) throw ArgumentError('$list contains no null elements.');
   list[index] = element;
 }
 
 /// Sets the element of [list] that currently contains [element] to `null`.
 void replaceWithNull<E>(List<E> list, E element) {
-  var index = list.indexOf(element);
+  final index = list.indexOf(element);
   if (index < 0) {
-    throw ArgumentError("$list contains no elements matching $element.");
+    throw ArgumentError('$list contains no elements matching $element.');
   }
 
   list[index] = null;
diff --git a/pubspec.yaml b/pubspec.yaml
index 2054423..fce2124 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,8 +1,7 @@
 name: source_span
-version: 1.6.0
+version: 1.6.1-dev
 
 description: A library for identifying source spans and locations.
-author: Dart Team <misc@dartlang.org>
 homepage: https://github.com/dart-lang/source_span
 
 environment:
diff --git a/test/multiple_highlight_test.dart b/test/multiple_highlight_test.dart
index f0cceed..d9d1b30 100644
--- a/test/multiple_highlight_test.dart
+++ b/test/multiple_highlight_test.dart
@@ -26,13 +26,13 @@
 fwee fwoo fwip
 argle bargle boo
 gibble bibble bop
-''', url: "file1.txt");
+''', url: 'file1.txt');
   });
 
-  test("highlights spans on separate lines", () {
+  test('highlights spans on separate lines', () {
     expect(
         file.span(17, 21).highlightMultiple(
-            "one", {file.span(31, 34): "two", file.span(4, 7): "three"}),
+            'one', {file.span(31, 34): 'two', file.span(4, 7): 'three'}),
         equals("""
   ,
 1 | foo bar baz
@@ -44,10 +44,10 @@
   '"""));
   });
 
-  test("highlights spans on the same line", () {
+  test('highlights spans on the same line', () {
     expect(
         file.span(17, 21).highlightMultiple(
-            "one", {file.span(22, 26): "two", file.span(12, 16): "three"}),
+            'one', {file.span(22, 26): 'two', file.span(12, 16): 'three'}),
         equals("""
   ,
 2 | whiz bang boom
@@ -57,10 +57,10 @@
   '"""));
   });
 
-  test("highlights overlapping spans on the same line", () {
+  test('highlights overlapping spans on the same line', () {
     expect(
         file.span(17, 21).highlightMultiple(
-            "one", {file.span(20, 26): "two", file.span(12, 18): "three"}),
+            'one', {file.span(20, 26): 'two', file.span(12, 18): 'three'}),
         equals("""
   ,
 2 | whiz bang boom
@@ -70,10 +70,10 @@
   '"""));
   });
 
-  test("highlights multiple multiline spans", () {
+  test('highlights multiple multiline spans', () {
     expect(
         file.span(27, 54).highlightMultiple(
-            "one", {file.span(54, 89): "two", file.span(0, 27): "three"}),
+            'one', {file.span(54, 89): 'two', file.span(0, 27): 'three'}),
         equals("""
   ,
 1 | / foo bar baz
@@ -88,10 +88,10 @@
   '"""));
   });
 
-  test("highlights multiple overlapping multiline spans", () {
+  test('highlights multiple overlapping multiline spans', () {
     expect(
         file.span(12, 70).highlightMultiple(
-            "one", {file.span(54, 89): "two", file.span(0, 27): "three"}),
+            'one', {file.span(54, 89): 'two', file.span(0, 27): 'three'}),
         equals("""
   ,
 1 | /- foo bar baz
@@ -106,12 +106,12 @@
   '"""));
   });
 
-  test("highlights many layers of overlaps", () {
+  test('highlights many layers of overlaps', () {
     expect(
-        file.span(0, 54).highlightMultiple("one", {
-          file.span(12, 77): "two",
-          file.span(27, 84): "three",
-          file.span(39, 88): "four"
+        file.span(0, 54).highlightMultiple('one', {
+          file.span(12, 77): 'two',
+          file.span(27, 84): 'three',
+          file.span(39, 88): 'four'
         }),
         equals("""
   ,
@@ -129,11 +129,11 @@
   });
 
   group("highlights a multiline span that's a subset", () {
-    test("with no first or last line overlap", () {
+    test('with no first or last line overlap', () {
       expect(
           file
               .span(27, 53)
-              .highlightMultiple("inner", {file.span(12, 70): "outer"}),
+              .highlightMultiple('inner', {file.span(12, 70): 'outer'}),
           equals("""
   ,
 2 | /- whiz bang boom
@@ -145,11 +145,11 @@
   '"""));
     });
 
-    test("overlapping the whole first line", () {
+    test('overlapping the whole first line', () {
       expect(
           file
               .span(12, 53)
-              .highlightMultiple("inner", {file.span(12, 70): "outer"}),
+              .highlightMultiple('inner', {file.span(12, 70): 'outer'}),
           equals("""
   ,
 2 | // whiz bang boom
@@ -161,11 +161,11 @@
   '"""));
     });
 
-    test("overlapping part of first line", () {
+    test('overlapping part of first line', () {
       expect(
           file
               .span(17, 53)
-              .highlightMultiple("inner", {file.span(12, 70): "outer"}),
+              .highlightMultiple('inner', {file.span(12, 70): 'outer'}),
           equals("""
   ,
 2 | /- whiz bang boom
@@ -178,11 +178,11 @@
   '"""));
     });
 
-    test("overlapping the whole last line", () {
+    test('overlapping the whole last line', () {
       expect(
           file
               .span(27, 70)
-              .highlightMultiple("inner", {file.span(12, 70): "outer"}),
+              .highlightMultiple('inner', {file.span(12, 70): 'outer'}),
           equals("""
   ,
 2 | /- whiz bang boom
@@ -194,11 +194,11 @@
   '"""));
     });
 
-    test("overlapping part of the last line", () {
+    test('overlapping part of the last line', () {
       expect(
           file
               .span(27, 66)
-              .highlightMultiple("inner", {file.span(12, 70): "outer"}),
+              .highlightMultiple('inner', {file.span(12, 70): 'outer'}),
           equals("""
   ,
 2 | /- whiz bang boom
@@ -211,12 +211,12 @@
     });
   });
 
-  group("a single-line span in a multiline span", () {
-    test("on the first line", () {
+  group('a single-line span in a multiline span', () {
+    test('on the first line', () {
       expect(
           file
               .span(17, 21)
-              .highlightMultiple("inner", {file.span(12, 70): "outer"}),
+              .highlightMultiple('inner', {file.span(12, 70): 'outer'}),
           equals("""
   ,
 2 | / whiz bang boom
@@ -228,11 +228,11 @@
   '"""));
     });
 
-    test("in the middle", () {
+    test('in the middle', () {
       expect(
           file
               .span(31, 34)
-              .highlightMultiple("inner", {file.span(12, 70): "outer"}),
+              .highlightMultiple('inner', {file.span(12, 70): 'outer'}),
           equals("""
   ,
 2 | / whiz bang boom
@@ -244,11 +244,11 @@
   '"""));
     });
 
-    test("on the last line", () {
+    test('on the last line', () {
       expect(
           file
               .span(60, 66)
-              .highlightMultiple("inner", {file.span(12, 70): "outer"}),
+              .highlightMultiple('inner', {file.span(12, 70): 'outer'}),
           equals("""
   ,
 2 | / whiz bang boom
@@ -261,13 +261,13 @@
     });
   });
 
-  test("highlights multiple files with their URLs", () {
-    var file2 = SourceFile.fromString('''
+  test('highlights multiple files with their URLs', () {
+    final file2 = SourceFile.fromString('''
 quibble bibble boop
-''', url: "file2.txt");
+''', url: 'file2.txt');
 
     expect(
-        file.span(31, 34).highlightMultiple("one", {file2.span(8, 14): "two"}),
+        file.span(31, 34).highlightMultiple('one', {file2.span(8, 14): 'two'}),
         equals("""
   ,--> file1.txt
 3 | zip zap zop