improve import URI completions at EOF

pkg/analysis_server/lib/src/services/completion/dart/uri_contributor.dart

 // Copyright (c) 2014, 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 services.completion.contributor.dart.importuri;
 
 import 'dart:async';
 import 'dart:core';
 
 import 'package:analysis_server/src/provisional/completion/dart/completion_dart.dart';
@@ skipping 37 matching lines @@
 
   @override
   visitImportDirective(ImportDirective node) {
     visitNamespaceDirective(node);
   }
 
   visitNamespaceDirective(NamespaceDirective node) {
     StringLiteral uri = node.uri;
     if (uri is SimpleStringLiteral) {
       int offset = request.offset;
-      if (uri.offset < offset &&
-          (offset < uri.end || offset == uri.offset + 1)) {
-        // Handle degenerate case where import or export is only line in file
-        // and there is no semicolon
-        visitSimpleStringLiteral(uri);
+      int start = uri.offset;
+      int end = uri.end;
+      if (offset > start) {
+        if (offset < end) {
+          // Quoted non-empty string
+          visitSimpleStringLiteral(uri);
+        } else if (offset == end) {
+          if (end == start + 1) {
+            // Quoted empty string
+            visitSimpleStringLiteral(uri);
+          } else {
+            String data = request.source.contents.data;
+            if (end == data.length) {
+              String ch = data[end - 1];
+              if (ch != '"' && ch != "'") {
+                // Insertion point at end of file
+                // and missing closing quote on non-empty string
+                visitSimpleStringLiteral(uri);
+              }
+            }
+          }
+        }
+      }
+      else if (offset == start && offset == end) {
+        String data = request.source.contents.data;
+        if (end == data.length) {
+          String ch = data[end - 1];
+          if (ch == '"' || ch == "'") {
+            // Insertion point at end of file
+            // and missing closing quote on empty string
+            visitSimpleStringLiteral(uri);
+          }
+        }
       }
     }
   }
 
   @override
   visitSimpleStringLiteral(SimpleStringLiteral node) {
     AstNode parent = node.parent;
     if (parent is NamespaceDirective && parent.uri == node) {
       String partialUri = _extractPartialUri(node);
       if (partialUri != null) {
@@ skipping 114 matching lines @@
   }
 
   String _extractPartialUri(SimpleStringLiteral node) {
     if (request.offset < node.contentsOffset) {
       return null;
     }
     return node.literal.lexeme.substring(
         node.contentsOffset - node.offset, request.offset - node.offset);
   }
 }