Handle files disappearing during analysis (#3390)

packages/flutter_tools/lib/src/commands/analyze.dart

@@ -363,22 +363,14 @@ class AnalyzeCommand extends FlutterCommand {
           String errorMessage = groups[2];
           int lineNumber = int.parse(groups[4]);
           int colNumber = int.parse(groups[5]);
+          try {
             File source = new File(filename);
             List<String> sourceLines = source.readAsLinesSync();
-          String sourceLine;
-          try {
             if (lineNumber > sourceLines.length)
               throw new FileChanged();
-            sourceLine = sourceLines[lineNumber-1];
+            String sourceLine = sourceLines[lineNumber-1];
             if (colNumber > sourceLine.length)
               throw new FileChanged();
-          } on FileChanged {
-            if (changedFiles.add(filename))
-              printError('[warning] File shrank during analysis ($filename)');
-            sourceLine = '';
-            lineNumber = 1;
-            colNumber = 1;
-          }
             bool shouldIgnore = false;
             if (documentAllMembersPattern.firstMatch(errorMessage) != null) {
               // https://github.com/dart-lang/linter/issues/207
@@ -410,6 +402,13 @@ class AnalyzeCommand extends FlutterCommand {
             }
             if (shouldIgnore)
               continue;
+          } on FileSystemException catch (exception) {
+            if (changedFiles.add(filename))
+              printError('[warning] Could not read file (${exception.message}${ exception.osError != null ? "; ${exception.osError}" : ""}) ($filename)');
+          } on FileChanged {
+            if (changedFiles.add(filename))
+              printError('[warning] File shrank during analysis ($filename)');
+          }
         }
         printError(errorLine);
         errorCount += 1;