Add SdkPatcher and implement top-level function / getter / setter patching.

pkg/analyzer/lib/src/dart/sdk/patch.dart

+// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+library analyzer.src.dart.sdk.patch;
+
+import 'package:analyzer/dart/ast/ast.dart';
+import 'package:analyzer/dart/ast/token.dart';
+import 'package:analyzer/error/listener.dart';
+import 'package:analyzer/file_system/file_system.dart';
+import 'package:analyzer/src/dart/scanner/reader.dart';
+import 'package:analyzer/src/dart/scanner/scanner.dart';
+import 'package:analyzer/src/dart/sdk/sdk.dart';
+import 'package:analyzer/src/generated/parser.dart';
+import 'package:analyzer/src/generated/sdk.dart';
+import 'package:analyzer/src/generated/source.dart';
+import 'package:meta/meta.dart';
+import 'package:path/src/context.dart';
+
+/**
+ * [SdkPatcher] applies patches to SDK [CompilationUnit].
+ */
+class SdkPatcher {
+  /**
+   * Patch the given [unit] of a SDK [source] with the patches defined in
+   * the [sdk] for the given [platform].  Throw [ArgumentError] if a patch
+   * file cannot be read, or the contents violates rules for patch files.
+   *
+   * If [addNewTopLevelDeclarations] is `true`, then the [unit] is the
+   * defining unit of a library, so new top-level declarations should be
+   * added to this unit.  For parts new declarations may be added only to the
+   * patched classes.
+   *
+   * TODO(scheglov) auto-detect [addNewTopLevelDeclarations]
+   */
+  void patch(DartSdk sdk, int platform, AnalysisErrorListener errorListener,
+      Source source, CompilationUnit unit,
+      {bool addNewTopLevelDeclarations: true}) {
+    if (sdk is FolderBasedDartSdk) {

[Paul Berry, 2016/10/11 20:24:45]

Will sdk ever not be FolderBasedDartSdk?  What should happen in that case?  It
could mask bugs if someone accidentally passes the wrong type to this function
and nothing happens.  Maybe it would be better to just change the argument type
to FolderBasedDartSdk so there's no confusion.

[scheglov, 2016/10/11 20:34:08]

Done.

+      // Prepare the patch files to apply.
+      List<String> patchPaths;
+      {
+        String uriStr = source.uri.toString();
+        SdkLibrary sdkLibrary = sdk.getSdkLibrary(uriStr);

[Paul Berry, 2016/10/11 20:24:45]

When patching a file that is a "part" of an SDK library, I think this will
return null, triggering the exception below.

[scheglov, 2016/10/11 20:34:08]

I will add TODO for now.

+        if (sdkLibrary == null) {
+          throw new ArgumentError(
+              'The library $uriStr is not defined in the SDK.');
+        }
+        patchPaths = sdkLibrary.getPatches(platform);
+      }
+
+      bool strongMode = sdk.analysisOptions.strongMode;
+      Context pathContext = sdk.resourceProvider.pathContext;
+      for (String path in patchPaths) {
+        String pathInLib = pathContext.joinAll(path.split('/'));
+        File patchFile = sdk.libraryDirectory.getChildAssumingFile(pathInLib);
+        if (!patchFile.exists) {
+          throw new ArgumentError(
+              'The patch file ${patchFile.path} does not exist.');
+        }
+        Source patchSource = patchFile.createSource();
+        CompilationUnit patchUnit =
+            parse(patchSource, strongMode, errorListener);
+        _patchTopLevelDeclarations(
+            source, unit, patchSource, patchUnit, addNewTopLevelDeclarations);
+      }
+    }
+  }
+
+  void _failExternalKeyword(Source source, String name, int offset) {
+    throw new ArgumentError(
+        'The keyword "external" was expected for "$name" in $source @ $offset.');
+  }
+
+  void _patchTopLevelDeclarations(
+      Source baseSource,
+      CompilationUnit baseUnit,
+      Source patchSource,
+      CompilationUnit patchUnit,
+      bool addNewTopLevelDeclarations) {
+    List<CompilationUnitMember> declarationsToAppend = [];
+    for (CompilationUnitMember patchDeclaration in patchUnit.declarations) {
+      if (patchDeclaration is FunctionDeclaration) {
+        String name = patchDeclaration.name.name;
+        if (_hasPatchAnnotation(patchDeclaration.metadata)) {
+          for (CompilationUnitMember baseDeclaration in baseUnit.declarations) {
+            if (patchDeclaration is FunctionDeclaration &&
+                baseDeclaration is FunctionDeclaration &&
+                baseDeclaration.name.name == name) {
+              if (_hasPatchAnnotation(patchDeclaration.metadata)) {
+                // Remove the "external" keyword.
+                if (baseDeclaration.externalKeyword != null) {
+                  baseDeclaration.externalKeyword = null;
+                } else {
+                  _failExternalKeyword(
+                      baseSource, name, baseDeclaration.offset);
+                }
+                // Replace the body.
+                baseDeclaration.functionExpression.body =
+                    patchDeclaration.functionExpression.body;
+              }
+            }
+          }
+        } else if (addNewTopLevelDeclarations) {
+          // No @patch, must be private.
+          if (!Identifier.isPrivateName(name)) {
+            throw new ArgumentError(
+                'The patch file $patchSource attempts to append '
+                'a non-private declaration "$name".');
+          }
+          declarationsToAppend.add(patchDeclaration);
+        }
+      }
+    }
+    // Append new top-level declarations.
+    baseUnit.declarations.addAll(declarationsToAppend);
+  }
+
+  /**
+   * Parse the given [source] into AST.
+   */
+  @visibleForTesting
+  static CompilationUnit parse(
+      Source source, bool strong, AnalysisErrorListener errorListener) {
+    String code = source.contents.data;
+
+    CharSequenceReader reader = new CharSequenceReader(code);
+    Scanner scanner = new Scanner(source, reader, errorListener);
+    scanner.scanGenericMethodComments = strong;
+    Token token = scanner.tokenize();
+    LineInfo lineInfo = new LineInfo(scanner.lineStarts);
+
+    Parser parser = new Parser(source, errorListener);
+    parser.parseGenericMethodComments = strong;
+    CompilationUnit unit = parser.parseCompilationUnit(token);
+    unit.lineInfo = lineInfo;
+    return unit;
+  }
+
+  /**
+   * Return `true` if [metadata] has the `@patch` annotation.
+   */
+  static bool _hasPatchAnnotation(List<Annotation> metadata) {
+    return metadata.any((annotation) {
+      Identifier name = annotation.name;
+      return annotation.constructorName == null &&
+          name is SimpleIdentifier &&
+          name.name == 'patch';
+    });
+  }
+}