Issue 26335. Insert an empty line if the class body is a single line.

pkg/analysis_server/lib/src/services/correction/fix_internal.dart

Index: pkg/analysis_server/lib/src/services/correction/fix_internal.dart
diff --git a/pkg/analysis_server/lib/src/services/correction/fix_internal.dart b/pkg/analysis_server/lib/src/services/correction/fix_internal.dart
index 17c7822649c962ded4c1e1a764a52d0303d1e66a..b64f4289f66c8c1fade91fcb0184cd1e52ed53ee 100644
--- a/pkg/analysis_server/lib/src/services/correction/fix_internal.dart
+++ b/pkg/analysis_server/lib/src/services/correction/fix_internal.dart
@@ -697,14 +697,12 @@ class FixProcessor {
       }
     }
     // prepare location for a new constructor
-    _ConstructorLocation targetLocation =
+    _ClassMemberLocation targetLocation =
         _prepareNewConstructorLocation(classDeclaration);
     // build constructor source
     SourceBuilder sb = new SourceBuilder(file, targetLocation.offset);
     {
-      String indent = '  ';
       sb.append(targetLocation.prefix);
-      sb.append(indent);
       sb.append(classDeclaration.name.name);
       sb.append('(');
       sb.append(fieldNames.map((name) => 'this.$name').join(', '));
@@ -743,19 +741,17 @@ class FixProcessor {
     if (targetTypeNode is! ClassDeclaration) {
       return;
     }
-    _ConstructorLocation targetLocation =
+    _ClassMemberLocation targetLocation =
         _prepareNewConstructorLocation(targetTypeNode);
     String targetFile = targetElement.source.fullName;
     // build method source
     SourceBuilder sb = new SourceBuilder(targetFile, targetLocation.offset);
     {
-      String indent = '  ';
       sb.append(targetLocation.prefix);
-      sb.append(indent);
       sb.append(targetElement.name);
       _addFix_undefinedMethod_create_parameters(
           sb, instanceCreation.argumentList);
-      sb.append(') {$eol$indent}');
+      sb.append(');');
       sb.append(targetLocation.suffix);
     }
     // insert source
@@ -801,15 +797,13 @@ class FixProcessor {
     if (targetTypeNode is! ClassDeclaration) {
       return;
     }
-    _ConstructorLocation targetLocation =
+    _ClassMemberLocation targetLocation =
         _prepareNewConstructorLocation(targetTypeNode);
     String targetFile = targetElement.source.fullName;
     // build method source
     SourceBuilder sb = new SourceBuilder(targetFile, targetLocation.offset);
     {
-      String indent = '  ';
       sb.append(targetLocation.prefix);
-      sb.append(indent);
       sb.append(targetElement.name);
       sb.append('.');
       // append name
@@ -820,7 +814,7 @@ class FixProcessor {
       }
       _addFix_undefinedMethod_create_parameters(
           sb, instanceCreation.argumentList);
-      sb.append(') {$eol$indent}');
+      sb.append(');');
       sb.append(targetLocation.suffix);
     }
     // insert source
@@ -941,13 +935,11 @@ class FixProcessor {
         argumentsBuffer.append(parameterName);
       }
       // add proposal
-      _ConstructorLocation targetLocation =
+      _ClassMemberLocation targetLocation =
           _prepareNewConstructorLocation(targetClassNode);
       SourceBuilder sb = new SourceBuilder(file, targetLocation.offset);
       {
-        String indent = utils.getIndent(1);
         sb.append(targetLocation.prefix);
-        sb.append(indent);
         sb.append(targetClassName);
         if (!constructorName.isEmpty) {
           sb.startPosition('NAME');
@@ -1025,7 +1017,8 @@ class FixProcessor {
     }
     ClassDeclaration targetClassNode = targetTypeNode;
     // prepare location
-    _FieldLocation targetLocation = _prepareNewFieldLocation(targetClassNode);
+    _ClassMemberLocation targetLocation =
+        _prepareNewFieldLocation(targetClassNode);
     // build method source
     String targetFile = targetClassElement.source.fullName;
     SourceBuilder sb = new SourceBuilder(targetFile, targetLocation.offset);
@@ -1157,7 +1150,8 @@ class FixProcessor {
     }
     ClassDeclaration targetClassNode = targetTypeNode;
     // prepare location
-    _FieldLocation targetLocation = _prepareNewGetterLocation(targetClassNode);
+    _ClassMemberLocation targetLocation =
+        _prepareNewGetterLocation(targetClassNode);
     // build method source
     String targetFile = targetClassElement.source.fullName;
     SourceBuilder sb = new SourceBuilder(targetFile, targetLocation.offset);
@@ -1284,7 +1278,7 @@ class FixProcessor {
     // EOL management
     bool isFirst = true;
     void addEolIfNotFirst() {
-      if (!isFirst || !targetClass.members.isEmpty) {
+      if (!isFirst || _isClassWithEmptyBody(targetClass)) {
         sb.append(eol);
       }
       isFirst = false;
@@ -2739,74 +2733,62 @@ class FixProcessor {
     return node is SimpleIdentifier && node.name == 'await';
   }
 
-  _ConstructorLocation _prepareNewConstructorLocation(
-      ClassDeclaration classDeclaration) {
-    List<ClassMember> members = classDeclaration.members;
-    // find the last field/constructor
-    ClassMember lastFieldOrConstructor = null;
-    for (ClassMember member in members) {
-      if (member is FieldDeclaration || member is ConstructorDeclaration) {
-        lastFieldOrConstructor = member;
-      } else {
-        break;
-      }
-    }
-    // after the last field/constructor
-    if (lastFieldOrConstructor != null) {
-      return new _ConstructorLocation(
-          eol + eol, lastFieldOrConstructor.end, '');
-    }
-    // at the beginning of the class
-    String suffix = members.isEmpty ? '' : eol;
-    return new _ConstructorLocation(
-        eol, classDeclaration.leftBracket.end, suffix);
+  /**
+   * Return `true` if the given [classDeclaration] has open '{' and close '}'
+   * at the same line, e.g. `class X {}`.
+   */
+  bool _isClassWithEmptyBody(ClassDeclaration classDeclaration) {
+    return utils.getLineThis(classDeclaration.leftBracket.offset) ==
+        utils.getLineThis(classDeclaration.rightBracket.offset);
   }
 
-  _FieldLocation _prepareNewFieldLocation(ClassDeclaration classDeclaration) {
+  _ClassMemberLocation _prepareNewClassMemberLocation(
+      ClassDeclaration classDeclaration,
+      bool shouldSkip(ClassMember existingMember)) {
     String indent = utils.getIndent(1);
-    // find the last field
-    ClassMember lastFieldOrConstructor = null;
+    // Find the last target member.
+    ClassMember targetMember = null;
     List<ClassMember> members = classDeclaration.members;
     for (ClassMember member in members) {
-      if (member is FieldDeclaration) {
-        lastFieldOrConstructor = member;
+      if (shouldSkip(member)) {
+        targetMember = member;
       } else {
         break;
       }
     }
-    // after the last field
-    if (lastFieldOrConstructor != null) {
-      return new _FieldLocation(
-          eol + eol + indent, lastFieldOrConstructor.end, '');
+    // After the last target member.
+    if (targetMember != null) {
+      return new _ClassMemberLocation(eol + eol + indent, targetMember.end, '');
     }
-    // at the beginning of the class
-    String suffix = members.isEmpty ? '' : eol;
-    return new _FieldLocation(
+    // At the beginning of the class.
+    String suffix = members.isNotEmpty ||
+        _isClassWithEmptyBody(classDeclaration) ? eol : '';
+    return new _ClassMemberLocation(
         eol + indent, classDeclaration.leftBracket.end, suffix);
   }
 
-  _FieldLocation _prepareNewGetterLocation(ClassDeclaration classDeclaration) {
-    String indent = utils.getIndent(1);
-    // find an existing target member
-    ClassMember prevMember = null;
-    List<ClassMember> members = classDeclaration.members;
-    for (ClassMember member in members) {
-      if (member is FieldDeclaration ||
-          member is ConstructorDeclaration ||
-          member is MethodDeclaration && member.isGetter) {
-        prevMember = member;
-      } else {
-        break;
-      }
-    }
-    // after the last field/getter
-    if (prevMember != null) {
-      return new _FieldLocation(eol + eol + indent, prevMember.end, '');
-    }
-    // at the beginning of the class
-    String suffix = members.isEmpty ? '' : eol;
-    return new _FieldLocation(
-        eol + indent, classDeclaration.leftBracket.end, suffix);
+  _ClassMemberLocation _prepareNewConstructorLocation(
+      ClassDeclaration classDeclaration) {
+    return _prepareNewClassMemberLocation(
+        classDeclaration,
+        (member) =>
+            member is FieldDeclaration || member is ConstructorDeclaration);
+  }
+
+  _ClassMemberLocation _prepareNewFieldLocation(
+      ClassDeclaration classDeclaration) {
+    return _prepareNewClassMemberLocation(
+        classDeclaration, (member) => member is FieldDeclaration);
+  }
+
+  _ClassMemberLocation _prepareNewGetterLocation(
+      ClassDeclaration classDeclaration) {
+    return _prepareNewClassMemberLocation(
+        classDeclaration,
+        (member) =>
+            member is FieldDeclaration ||
+            member is ConstructorDeclaration ||
+            member is MethodDeclaration && member.isGetter);
   }
 
   /**
@@ -2928,6 +2910,17 @@ class LintNames {
 }
 
 /**
+ * Describes the location for a newly created [ClassMember].
+ */
+class _ClassMemberLocation {
+  final String prefix;
+  final int offset;
+  final String suffix;
+
+  _ClassMemberLocation(this.prefix, this.offset, this.suffix);
+}
+
+/**
  * Helper for finding [Element] with name closest to the given.
  */
 class _ClosestElementFinder {
@@ -2955,25 +2948,3 @@ class _ClosestElementFinder {
     }
   }
 }
-
-/**
- * Describes the location for a newly created [ConstructorDeclaration].
- */
-class _ConstructorLocation {
-  final String prefix;
-  final int offset;
-  final String suffix;
-
-  _ConstructorLocation(this.prefix, this.offset, this.suffix);
-}
-
-/**
- * Describes the location for a newly created [FieldDeclaration].
- */
-class _FieldLocation {
-  final String prefix;
-  final int offset;
-  final String suffix;
-
-  _FieldLocation(this.prefix, this.offset, this.suffix);
-}