Emit CSS for used modules (#620)

lib/src/async_environment.dart

@@ -29,6 +29,10 @@ class AsyncEnvironment {
   /// This is `null` if there are no namespaceless modules.
   Set<AsyncModule> _globalModules;
 
+  /// Modules from both [_modules] and [_global], in the order in which they
+  /// were `@use`d.
+  final List<AsyncModule> _allModules;
+
   /// A list of variables defined at each lexical scope level.
   ///
   /// Each scope maps the names of declared variables to their values. These
@@ -122,6 +126,7 @@ class AsyncEnvironment {
   AsyncEnvironment({bool sourceMap = false})
       : _modules = {},
         _globalModules = null,
+        _allModules = [],
         _variables = [normalizedMap()],
         _variableNodes = sourceMap ? [normalizedMap()] : null,
         _variableIndices = normalizedMap(),
@@ -132,8 +137,15 @@ class AsyncEnvironment {
     coreFunctions.forEach(setFunction);
   }
 
-  AsyncEnvironment._(this._modules, this._globalModules, this._variables,
+  AsyncEnvironment._(
-      this._variableNodes, this._functions, this._mixins, this._content)
+      this._modules,
+      this._globalModules,
+      this._allModules,
+      this._variables,
+      this._variableNodes,
+      this._functions,
+      this._mixins,
+      this._content)
       // Lazily fill in the indices rather than eagerly copying them from the
       // existing environment in closure() because the copying took a lot of
       // time and was rarely helpful. This saves a bunch of time on Susy's
@@ -150,6 +162,7 @@ class AsyncEnvironment {
   AsyncEnvironment closure() => AsyncEnvironment._(
       _modules,
       _globalModules,
+      _allModules,
       _variables.toList(),
       _variableNodes?.toList(),
       _functions.toList(),
@@ -160,8 +173,10 @@ class AsyncEnvironment {
   ///
   /// The returned environment shares this environment's global variables,
   /// functions, and mixins, but not its modules.
-  AsyncEnvironment global() => AsyncEnvironment._({},
+  AsyncEnvironment global() => AsyncEnvironment._(
+      {},
       null,
+      [],
       _variables.toList(),
       _variableNodes?.toList(),
       _functions.toList(),
@@ -180,6 +195,7 @@ class AsyncEnvironment {
     if (namespace == null) {
       _globalModules ??= Set();
       _globalModules.add(module);
+      _allModules.add(module);
 
       for (var name in _variables.first.keys) {
         if (module.variables.containsKey(name)) {
@@ -195,6 +211,7 @@ class AsyncEnvironment {
       }
 
       _modules[namespace] = module;
+      _allModules.add(module);
     }
   }
 
@@ -600,6 +617,7 @@ class AsyncEnvironment {
 
 /// A module that represents the top-level members defined in an [Environment].
 class _EnvironmentModule implements AsyncModule {
+  final List<AsyncModule> upstream;
   final Map<String, Value> variables;
   final Map<String, AstNode> variableNodes;
   final Map<String, AsyncCallable> functions;
@@ -612,7 +630,8 @@ class _EnvironmentModule implements AsyncModule {
   // TODO(nweiz): Use custom [UnmodifiableMapView]s that forbid access to
   // private members.
   _EnvironmentModule(this._environment, this.css)
-      : variables = PublicMemberMap(_environment._variables.first),
+      : upstream = _environment._allModules,
+        variables = PublicMemberMap(_environment._variables.first),
         variableNodes = _environment._variableNodes == null
             ? null
             : PublicMemberMap(_environment._variableNodes.first),

lib/src/async_module.dart

@@ -11,6 +11,9 @@ import 'value.dart';
 
 /// The interface for a Sass module.
 abstract class AsyncModule {
+  /// Modules that this module uses.
+  List<AsyncModule> get upstream;
+
   /// The module's variables.
   Map<String, Value> get variables;
 

lib/src/environment.dart

@@ -5,7 +5,7 @@
 // DO NOT EDIT. This file was generated from async_environment.dart.
 // See tool/synchronize.dart for details.
 //
-// Checksum: 77b03257b1770270e2d1f269281bdaab3f9f1ae9
+// Checksum: e1d3693a4ede6e31d259efb13148a669be01e98c
 //
 // ignore_for_file: unused_import
 
@@ -34,6 +34,10 @@ class Environment {
   /// This is `null` if there are no namespaceless modules.
   Set<Module> _globalModules;
 
+  /// Modules from both [_modules] and [_global], in the order in which they
+  /// were `@use`d.
+  final List<Module> _allModules;
+
   /// A list of variables defined at each lexical scope level.
   ///
   /// Each scope maps the names of declared variables to their values. These
@@ -127,6 +131,7 @@ class Environment {
   Environment({bool sourceMap = false})
       : _modules = {},
         _globalModules = null,
+        _allModules = [],
         _variables = [normalizedMap()],
         _variableNodes = sourceMap ? [normalizedMap()] : null,
         _variableIndices = normalizedMap(),
@@ -137,8 +142,15 @@ class Environment {
     coreFunctions.forEach(setFunction);
   }
 
-  Environment._(this._modules, this._globalModules, this._variables,
+  Environment._(
-      this._variableNodes, this._functions, this._mixins, this._content)
+      this._modules,
+      this._globalModules,
+      this._allModules,
+      this._variables,
+      this._variableNodes,
+      this._functions,
+      this._mixins,
+      this._content)
       // Lazily fill in the indices rather than eagerly copying them from the
       // existing environment in closure() because the copying took a lot of
       // time and was rarely helpful. This saves a bunch of time on Susy's
@@ -155,6 +167,7 @@ class Environment {
   Environment closure() => Environment._(
       _modules,
       _globalModules,
+      _allModules,
       _variables.toList(),
       _variableNodes?.toList(),
       _functions.toList(),
@@ -165,8 +178,10 @@ class Environment {
   ///
   /// The returned environment shares this environment's global variables,
   /// functions, and mixins, but not its modules.
-  Environment global() => Environment._({},
+  Environment global() => Environment._(
+      {},
       null,
+      [],
       _variables.toList(),
       _variableNodes?.toList(),
       _functions.toList(),
@@ -185,6 +200,7 @@ class Environment {
     if (namespace == null) {
       _globalModules ??= Set();
       _globalModules.add(module);
+      _allModules.add(module);
 
       for (var name in _variables.first.keys) {
         if (module.variables.containsKey(name)) {
@@ -200,6 +216,7 @@ class Environment {
       }
 
       _modules[namespace] = module;
+      _allModules.add(module);
     }
   }
 
@@ -602,6 +619,7 @@ class Environment {
 
 /// A module that represents the top-level members defined in an [Environment].
 class _EnvironmentModule implements Module {
+  final List<Module> upstream;
   final Map<String, Value> variables;
   final Map<String, AstNode> variableNodes;
   final Map<String, Callable> functions;
@@ -614,7 +632,8 @@ class _EnvironmentModule implements Module {
   // TODO(nweiz): Use custom [UnmodifiableMapView]s that forbid access to
   // private members.
   _EnvironmentModule(this._environment, this.css)
-      : variables = PublicMemberMap(_environment._variables.first),
+      : upstream = _environment._allModules,
+        variables = PublicMemberMap(_environment._variables.first),
         variableNodes = _environment._variableNodes == null
             ? null
             : PublicMemberMap(_environment._variableNodes.first),

lib/src/module.dart

@@ -5,7 +5,7 @@
 // DO NOT EDIT. This file was generated from async_module.dart.
 // See tool/synchronize.dart for details.
 //
-// Checksum: 5608be0fdb1bff974611b75d1bbcb364a15d4df2
+// Checksum: 759037174212e69cd0d9a7ebf55f6ee9f66072e8
 //
 // ignore_for_file: unused_import
 
@@ -18,6 +18,9 @@ import 'value.dart';
 
 /// The interface for a Sass module.
 abstract class Module {
+  /// Modules that this module uses.
+  List<Module> get upstream;
+
   /// The module's variables.
   Map<String, Value> get variables;
 

lib/src/visitor/async_evaluate.dart

@@ -242,7 +242,7 @@ class _EvaluateVisitor
     var module = await _execute(importer, node);
     _extender.finalize();
 
-    return EvaluateResult(module.css, _includedFiles);
+    return EvaluateResult(_combineCss(module), _includedFiles);
   }
 
   Future<Value> runExpression(Expression expression,
@@ -406,6 +406,47 @@ class _EvaluateVisitor
     return CssStylesheet(statements.build(), _root.span);
   }
 
+  /// Returns a new stylesheet containing [root]'s CSS as well as the CSS of all
+  /// modules transitively used by [root].
+  CssStylesheet _combineCss(AsyncModule root) {
+    if (root.upstream.isEmpty) return root.css;
+
+    var seen = Set<AsyncModule>();
+    var imports = <CssNode>[];
+    var css = <CssNode>[];
+
+    void visitModule(AsyncModule module) {
+      if (!seen.add(module)) return;
+      for (var module in module.upstream) {
+        visitModule(module);
+      }
+
+      var statements = module.css.children;
+      var index = _indexAfterImports(statements);
+      imports.addAll(statements.getRange(0, index));
+      css.addAll(statements.getRange(index, statements.length));
+    }
+
+    visitModule(root);
+
+    return CssStylesheet(imports + css, root.css.span);
+  }
+
+  /// Returns the index of the first node in [statements] that comes after all
+  /// static imports.
+  int _indexAfterImports(List<CssNode> statements) {
+    var lastImport = -1;
+    for (var i = 0; i < statements.length; i++) {
+      var statement = statements[i];
+      if (statement is CssImport) {
+        lastImport = i;
+      } else if (statement is! CssComment) {
+        break;
+      }
+    }
+    return lastImport + 1;
+  }
+
   // ## Statements
 
   Future<Value> visitStylesheet(Stylesheet node) async {

lib/src/visitor/evaluate.dart

@@ -5,7 +5,7 @@
 // DO NOT EDIT. This file was generated from async_evaluate.dart.
 // See tool/synchronize.dart for details.
 //
-// Checksum: ae0454752ee85a9094d0f0d0e6e8a252364b70a1
+// Checksum: da6068544fd58007ee2d44c2688063cbe4543e73
 //
 // ignore_for_file: unused_import
 
@@ -249,7 +249,7 @@ class _EvaluateVisitor
     var module = _execute(importer, node);
     _extender.finalize();
 
-    return EvaluateResult(module.css, _includedFiles);
+    return EvaluateResult(_combineCss(module), _includedFiles);
   }
 
   Value runExpression(Expression expression, {Map<String, Value> variables}) {
@@ -412,6 +412,47 @@ class _EvaluateVisitor
     return CssStylesheet(statements.build(), _root.span);
   }
 
+  /// Returns a new stylesheet containing [root]'s CSS as well as the CSS of all
+  /// modules transitively used by [root].
+  CssStylesheet _combineCss(Module root) {
+    if (root.upstream.isEmpty) return root.css;
+
+    var seen = Set<Module>();
+    var imports = <CssNode>[];
+    var css = <CssNode>[];
+
+    void visitModule(Module module) {
+      if (!seen.add(module)) return;
+      for (var module in module.upstream) {
+        visitModule(module);
+      }
+
+      var statements = module.css.children;
+      var index = _indexAfterImports(statements);
+      imports.addAll(statements.getRange(0, index));
+      css.addAll(statements.getRange(index, statements.length));
+    }
+
+    visitModule(root);
+
+    return CssStylesheet(imports + css, root.css.span);
+  }
+
+  /// Returns the index of the first node in [statements] that comes after all
+  /// static imports.
+  int _indexAfterImports(List<CssNode> statements) {
+    var lastImport = -1;
+    for (var i = 0; i < statements.length; i++) {
+      var statement = statements[i];
+      if (statement is CssImport) {
+        lastImport = i;
+      } else if (statement is! CssComment) {
+        break;
+      }
+    }
+    return lastImport + 1;
+  }
+
   // ## Statements
 
   Value visitStylesheet(Stylesheet node) {