Enable strict null checks

lib/sass.dart

@@ -5,6 +5,7 @@
 /// We strongly recommend importing this library with the prefix `sass`.
 library sass;
 
+import 'package:package_config/package_config_types.dart';
 import 'package:source_maps/source_maps.dart';
 
 import 'src/async_import_cache.dart';
@@ -14,7 +15,6 @@ import 'src/exception.dart';
 import 'src/import_cache.dart';
 import 'src/importer.dart';
 import 'src/logger.dart';
-import 'src/sync_package_resolver.dart';
 import 'src/syntax.dart';
 import 'src/visitor/serialize.dart';
 
@@ -48,11 +48,11 @@ export 'src/warn.dart' show warn;
 /// * Each load path specified in the `SASS_PATH` environment variable, which
 ///   should be semicolon-separated on Windows and colon-separated elsewhere.
 ///
-/// * `package:` resolution using [packageResolver], which is a
-///   [`SyncPackageResolver`][] from the `package_resolver` package. Note that
+/// * `package:` resolution using [packageConfig], which is a
+///   [`PackageConfig`][] from the `package_resolver` package. Note that
 ///   this is a shorthand for adding a [PackageImporter] to [importers].
 ///
-/// [`SyncPackageResolver`]: https://www.dartdocs.org/documentation/package_resolver/latest/package_resolver/SyncPackageResolver-class.html
+/// [`PackageConfig`]: https://pub.dev/documentation/package_config/latest/package_config.package_config/PackageConfig-class.html
 ///
 /// Dart functions that can be called from Sass may be passed using [functions].
 /// Each [Callable] defines a top-level function that will be invoked when the
@@ -90,7 +90,7 @@ String compile(String path,
     Logger logger,
     Iterable<Importer> importers,
     Iterable<String> loadPaths,
-    SyncPackageResolver packageResolver,
+    PackageConfig packageConfig,
     Iterable<Callable> functions,
     OutputStyle style,
     void sourceMap(SingleMapping map),
@@ -99,9 +99,7 @@ String compile(String path,
   var result = c.compile(path,
       logger: logger,
       importCache: ImportCache(importers,
-          logger: logger,
-          loadPaths: loadPaths,
-          packageResolver: packageResolver),
+          logger: logger, loadPaths: loadPaths, packageConfig: packageConfig),
       functions: functions,
       style: style,
       sourceMap: sourceMap != null,
@@ -132,11 +130,11 @@ String compile(String path,
 /// * Each load path specified in the `SASS_PATH` environment variable, which
 ///   should be semicolon-separated on Windows and colon-separated elsewhere.
 ///
-/// * `package:` resolution using [packageResolver], which is a
-///   [`SyncPackageResolver`][] from the `package_resolver` package. Note that
+/// * `package:` resolution using [packageConfig], which is a
+///   [`PackageConfig`][] from the `package_resolver` package. Note that
 ///   this is a shorthand for adding a [PackageImporter] to [importers].
 ///
-/// [`SyncPackageResolver`]: https://www.dartdocs.org/documentation/package_resolver/latest/package_resolver/SyncPackageResolver-class.html
+/// [`PackageConfig`]: https://pub.dev/documentation/package_config/latest/package_config.package_config/PackageConfig-class.html
 ///
 /// Dart functions that can be called from Sass may be passed using [functions].
 /// Each [Callable] defines a top-level function that will be invoked when the
@@ -178,7 +176,7 @@ String compileString(String source,
     bool color = false,
     Logger logger,
     Iterable<Importer> importers,
-    SyncPackageResolver packageResolver,
+    PackageConfig packageConfig,
     Iterable<String> loadPaths,
     Iterable<Callable> functions,
     OutputStyle style,
@@ -192,9 +190,7 @@ String compileString(String source,
       syntax: syntax ?? (indented ? Syntax.sass : Syntax.scss),
       logger: logger,
       importCache: ImportCache(importers,
-          logger: logger,
-          packageResolver: packageResolver,
-          loadPaths: loadPaths),
+          logger: logger, packageConfig: packageConfig, loadPaths: loadPaths),
       functions: functions,
       style: style,
       importer: importer,
@@ -214,7 +210,7 @@ Future<String> compileAsync(String path,
     {bool color = false,
     Logger logger,
     Iterable<AsyncImporter> importers,
-    SyncPackageResolver packageResolver,
+    PackageConfig packageConfig,
     Iterable<String> loadPaths,
     Iterable<AsyncCallable> functions,
     OutputStyle style,
@@ -223,9 +219,7 @@ Future<String> compileAsync(String path,
   var result = await c.compileAsync(path,
       logger: logger,
       importCache: AsyncImportCache(importers,
-          logger: logger,
-          loadPaths: loadPaths,
-          packageResolver: packageResolver),
+          logger: logger, loadPaths: loadPaths, packageConfig: packageConfig),
       functions: functions,
       style: style,
       sourceMap: sourceMap != null);
@@ -243,7 +237,7 @@ Future<String> compileStringAsync(String source,
     bool color = false,
     Logger logger,
     Iterable<AsyncImporter> importers,
-    SyncPackageResolver packageResolver,
+    PackageConfig packageConfig,
     Iterable<String> loadPaths,
     Iterable<AsyncCallable> functions,
     OutputStyle style,
@@ -257,9 +251,7 @@ Future<String> compileStringAsync(String source,
       syntax: syntax ?? (indented ? Syntax.sass : Syntax.scss),
       logger: logger,
       importCache: AsyncImportCache(importers,
-          logger: logger,
-          packageResolver: packageResolver,
-          loadPaths: loadPaths),
+          logger: logger, packageConfig: packageConfig, loadPaths: loadPaths),
       functions: functions,
       style: style,
       importer: importer,

lib/src/ast/sass/argument_declaration.dart

@@ -113,7 +113,7 @@ class ArgumentDeclaration implements SassNode {
           "Only ${arguments.length} "
               "${names.isEmpty ? '' : 'positional '}"
               "${pluralize('argument', arguments.length)} allowed, but "
-              "${positional} ${pluralize('was', positional, plural: 'were')} "
+              "$positional ${pluralize('was', positional, plural: 'were')} "
               "passed.",
           "invocation",
           {spanWithName: "declaration"});

lib/src/ast/sass/expression/number.dart

@@ -22,5 +22,5 @@ class NumberExpression implements Expression {
   T accept<T>(ExpressionVisitor<T> visitor) =>
       visitor.visitNumberExpression(this);
 
-  String toString() => "${value}${unit ?? ''}";
+  String toString() => "$value${unit ?? ''}";
 }

lib/src/ast/sass/statement/declaration.dart

@@ -36,7 +36,7 @@ class Declaration extends ParentStatement {
     if (isCustomProperty && value is! StringExpression) {
       throw ArgumentError(
           'Declarations whose names begin with "--" must have StringExpression '
-          'values (was `${value}` of type ${value.runtimeType}).');
+          'values (was `$value` of type ${value.runtimeType}).');
     }
   }
 

lib/src/ast/sass/statement/if_rule.dart

@@ -27,55 +27,62 @@ class IfRule implements Statement {
   /// The final, unconditional `@else` clause.
   ///
   /// This is `null` if there is no unconditional `@else`.
-  final IfClause lastClause;
+  final ElseClause lastClause;
 
   final FileSpan span;
 
   IfRule(Iterable<IfClause> clauses, this.span, {this.lastClause})
-      : clauses = List.unmodifiable(clauses) {
-    assert(clauses.every((clause) => clause.expression != null));
-    assert(lastClause?.expression == null);
-  }
+      : clauses = List.unmodifiable(clauses);
 
   T accept<T>(StatementVisitor<T> visitor) => visitor.visitIfRule(this);
 
   String toString() {
     var first = true;
-    return clauses.map((clause) {
-      var name = first ? 'if' : 'else';
-      first = false;
-      return '@$name ${clause.expression} {${clause.children.join(" ")}}';
-    }).join(' ');
+    var result = clauses
+        .map((clause) =>
+            "@${first ? 'if' : 'else if'} {${clause.children.join(' ')}}")
+        .join(' ');
+
+    var lastClause = this.lastClause;
+    if (lastClause != null) result += " $lastClause";
+    return result;
   }
 }
 
-/// A single clause in an `@if` rule.
-class IfClause {
-  /// The expression to evaluate to determine whether to run this rule, or
-  /// `null` if this is the final unconditional `@else` clause.
-  final Expression expression;
-
+/// The superclass of `@if` and `@else` clauses.
+abstract class IfRuleClause {
   /// The statements to evaluate if this clause matches.
   final List<Statement> children;
 
   /// Whether any of [children] is a variable, function, or mixin declaration.
   final bool hasDeclarations;
 
-  IfClause(Expression expression, Iterable<Statement> children)
-      : this._(expression, List.unmodifiable(children));
-
-  IfClause.last(Iterable<Statement> children)
-      : this._(null, List.unmodifiable(children));
+  IfRuleClause(Iterable<Statement /*!*/ > children)
+      : this._(List.unmodifiable(children));
 
-  IfClause._(this.expression, this.children)
+  IfRuleClause._(this.children)
       : hasDeclarations = children.any((child) =>
             child is VariableDeclaration ||
             child is FunctionRule ||
             child is MixinRule ||
             (child is ImportRule &&
                 child.imports.any((import) => import is DynamicImport)));
+}
+
+/// An `@if` or `@else if` clause in an `@if` rule.
+class IfClause extends IfRuleClause {
+  /// The expression to evaluate to determine whether to run this rule.
+  final Expression expression;
+
+  IfClause(this.expression, Iterable<Statement /*!*/ > children)
+      : super(children);
+
+  String toString() => "@if $expression {${children.join(' ')}}";
+}
+
+/// An `@else` clause in an `@if` rule.
+class ElseClause extends IfRuleClause {
+  ElseClause(Iterable<Statement /*!*/ > children) : super(children);
 
-  String toString() =>
-      (expression == null ? "@else" : "@if $expression") +
-      " {${children.join(' ')}}";
+  String toString() => "@else {${children.join(' ')}}";
 }

lib/src/ast/sass/supports_condition/operation.dart

@@ -31,7 +31,7 @@ class SupportsOperation implements SupportsCondition {
   }
 
   String toString() =>
-      "${_parenthesize(left)} ${operator} ${_parenthesize(right)}";
+      "${_parenthesize(left)} $operator ${_parenthesize(right)}";
 
   String _parenthesize(SupportsCondition condition) =>
       condition is SupportsNegation ||

lib/src/async_compile.dart

@@ -15,7 +15,6 @@ import 'importer.dart';
 import 'importer/node.dart';
 import 'io.dart';
 import 'logger.dart';
-import 'sync_package_resolver.dart';
 import 'syntax.dart';
 import 'utils.dart';
 import 'visitor/async_evaluate.dart';
@@ -77,7 +76,6 @@ Future<CompileResult> compileStringAsync(String source,
     NodeImporter nodeImporter,
     Iterable<AsyncImporter> importers,
     Iterable<String> loadPaths,
-    SyncPackageResolver packageResolver,
     AsyncImporter importer,
     Iterable<AsyncCallable> functions,
     OutputStyle style,

lib/src/async_import_cache.dart

@@ -3,6 +3,7 @@
 // https://opensource.org/licenses/MIT.
 
 import 'package:collection/collection.dart';
+import 'package:package_config/package_config_types.dart';
 import 'package:path/path.dart' as p;
 import 'package:tuple/tuple.dart';
 
@@ -11,8 +12,7 @@ import 'importer.dart';
 import 'importer/utils.dart';
 import 'io.dart';
 import 'logger.dart';
-import 'sync_package_resolver.dart';
-import 'utils.dart'; // ignore: unused_import
+import 'utils.dart';
 
 /// An in-memory cache of parsed stylesheets that have been imported by Sass.
 class AsyncImportCache {
@@ -52,16 +52,14 @@ class AsyncImportCache {
   /// * Each load path specified in the `SASS_PATH` environment variable, which
   ///   should be semicolon-separated on Windows and colon-separated elsewhere.
   ///
-  /// * `package:` resolution using [packageResolver], which is a
-  ///   [`SyncPackageResolver`][] from the `package_resolver` package. Note that
+  /// * `package:` resolution using [packageConfig], which is a
+  ///   [`PackageConfig`][] from the `package_config` package. Note that
   ///   this is a shorthand for adding a [PackageImporter] to [importers].
   ///
-  /// [`SyncPackageResolver`]: https://www.dartdocs.org/documentation/package_resolver/latest/package_resolver/SyncPackageResolver-class.html
+  /// [`PackageConfig`]: https://pub.dev/documentation/package_config/latest/package_config.package_config/PackageConfig-class.html
   AsyncImportCache(Iterable<AsyncImporter> importers,
-      {Iterable<String> loadPaths,
-      SyncPackageResolver packageResolver,
-      Logger logger})
-      : _importers = _toImporters(importers, loadPaths, packageResolver),
+      {Iterable<String> loadPaths, PackageConfig packageConfig, Logger logger})
+      : _importers = _toImporters(importers, loadPaths, packageConfig),
         _logger = logger ?? const Logger.stderr(),
         _canonicalizeCache = {},
         _importCache = {},
@@ -75,10 +73,10 @@ class AsyncImportCache {
         _importCache = {},
         _resultsCache = {};
 
-  /// Converts the user's [importers], [loadPaths], and [packageResolver]
+  /// Converts the user's [importers], [loadPaths], and [packageConfig]
   /// options into a single list of importers.
   static List<AsyncImporter> _toImporters(Iterable<AsyncImporter> importers,
-      Iterable<String> loadPaths, SyncPackageResolver packageResolver) {
+      Iterable<String> loadPaths, PackageConfig packageConfig) {
     var sassPath = getEnvironmentVariable('SASS_PATH');
     return [
       ...?importers,
@@ -87,7 +85,7 @@ class AsyncImportCache {
       if (sassPath != null)
         for (var path in sassPath.split(isWindows ? ';' : ':'))
           FilesystemImporter(path),
-      if (packageResolver != null) PackageImporter(packageResolver)
+      if (packageConfig != null) PackageImporter(packageConfig)
     ];
   }
 

lib/src/compile.dart

@@ -5,7 +5,7 @@
 // DO NOT EDIT. This file was generated from async_compile.dart.
 // See tool/grind/synchronize.dart for details.
 //
-// Checksum: b2cd6037efa37e300daa45ebed20cb4b61526161
+// Checksum: ef27d750f1d5305373fe9e712cf99697a21e0689
 //
 // ignore_for_file: unused_import
 
@@ -25,7 +25,6 @@ import 'importer.dart';
 import 'importer/node.dart';
 import 'io.dart';
 import 'logger.dart';
-import 'sync_package_resolver.dart';
 import 'syntax.dart';
 import 'utils.dart';
 import 'visitor/evaluate.dart';
@@ -87,7 +86,6 @@ CompileResult compileString(String source,
     NodeImporter nodeImporter,
     Iterable<Importer> importers,
     Iterable<String> loadPaths,
-    SyncPackageResolver packageResolver,
     Importer importer,
     Iterable<Callable> functions,
     OutputStyle style,