Make hot mode a little less aggressive about catching errors. (#8743)

It was resulting in weird situations where the tool would dump an
error message and stack but not quit, or would fail hard but then just
hang.

Instead, specifically catch errors you expect. As an example of this,
there's one error we expect from the DartDependencySetBuilder, so we
catch that one, turn it into a dedicated exception class, then in the
caller catch that specific exception.

packages/flutter_tools/lib/executable.dart

@@ -257,7 +257,7 @@ Future<File> _createLocalCrashReport(List<String> args, dynamic error, Chain cha
   buffer.writeln('flutter ${args.join(' ')}\n');
 
   buffer.writeln('## exception\n');
-  buffer.writeln('$error\n');
+  buffer.writeln('${error.runtimeType}: $error\n');
   buffer.writeln('```\n${chain.terse}```\n');
 
   buffer.writeln('## flutter doctor\n');

packages/flutter_tools/lib/src/dart/dependencies.dart

@@ -2,16 +2,16 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'package:analyzer/analyzer.dart';
+import 'package:analyzer/analyzer.dart' as analyzer;
 
 import '../base/file_system.dart';
 import '../dart/package_map.dart';
 
 class DartDependencySetBuilder {
   DartDependencySetBuilder(String mainScriptPath, String packagesFilePath) :
-        this._mainScriptPath = fs.path.canonicalize(mainScriptPath),
-        this._mainScriptUri = fs.path.toUri(mainScriptPath),
-        this._packagesFilePath = fs.path.canonicalize(packagesFilePath);
+    _mainScriptPath = fs.path.canonicalize(mainScriptPath),
+    _mainScriptUri = fs.path.toUri(mainScriptPath),
+    _packagesFilePath = fs.path.canonicalize(packagesFilePath);
 
   final String _mainScriptPath;
   final String _packagesFilePath;
@@ -25,19 +25,40 @@ class DartDependencySetBuilder {
 
     while (toProcess.isNotEmpty) {
       final Uri currentUri = toProcess.removeLast();
-      final CompilationUnit unit = _parse(currentUri.toFilePath());
-      for (Directive directive in unit.directives) {
-        if (!(directive is UriBasedDirective))
+      final analyzer.CompilationUnit unit = _parse(currentUri.toFilePath());
+      for (analyzer.Directive directive in unit.directives) {
+        if (!(directive is analyzer.UriBasedDirective))
           continue;
-        final UriBasedDirective uriBasedDirective = directive;
+        final analyzer.UriBasedDirective uriBasedDirective = directive;
         final String uriAsString = uriBasedDirective.uri.stringValue;
-        Uri resolvedUri = resolveRelativeUri(currentUri, Uri.parse(uriAsString));
+        Uri resolvedUri = analyzer.resolveRelativeUri(currentUri, Uri.parse(uriAsString));
         if (resolvedUri.scheme.startsWith('dart'))
           continue;
-        if (resolvedUri.scheme == 'package')
-          resolvedUri = packageMap.uriForPackage(resolvedUri);
+        if (resolvedUri.scheme == 'package') {
+          final Uri newResolvedUri = packageMap.uriForPackage(resolvedUri);
+          if (newResolvedUri == null) {
+            throw new DartDependencyException(
+              'The following Dart file:\n'
+              '  ${currentUri.toFilePath()}\n'
+              '...refers, in an import, to the following library:\n'
+              '  $resolvedUri\n'
+              'That library is in a package that is not known. Maybe you forgot to '
+              'mention it in your pubspec.yaml file?'
+            );
+          }
+          resolvedUri = newResolvedUri;
+        }
         final String path = fs.path.canonicalize(resolvedUri.toFilePath());
         if (!dependencies.contains(path)) {
+          if (!fs.isFileSync(path)) {
+            throw new DartDependencyException(
+              'The following Dart file:\n'
+              '  ${currentUri.toFilePath()}\n'
+              '...refers, in an import, to the following library:\n'
+              '  $path\n'
+              'Unfortunately, that library does not appear to exist on your file system.'
+            );
+          }
           dependencies.add(path);
           toProcess.add(resolvedUri);
         }
@@ -46,5 +67,42 @@ class DartDependencySetBuilder {
     return dependencies.toSet();
   }
 
-  CompilationUnit _parse(String path) => parseDirectives(fs.file(path).readAsStringSync(), name: path);
+  analyzer.CompilationUnit _parse(String path) {
+    String body;
+    try {
+      body = fs.file(path).readAsStringSync();
+    } on FileSystemException catch (error) {
+      throw new DartDependencyException(
+        'Could not read "$path" when determining Dart dependencies.',
+        error,
+      );
+    }
+    try {
+      return analyzer.parseDirectives(body, name: path);
+    } on analyzer.AnalyzerError catch (error) {
+      throw new DartDependencyException(
+        'When trying to parse this Dart file to find its dependencies:\n'
+        '  $path\n'
+        '...the analyzer failed with the following error:\n'
+        '  ${error.toString().trimRight()}',
+        error,
+      );
+    } on analyzer.AnalyzerErrorGroup catch (error) {
+      throw new DartDependencyException(
+        'When trying to parse this Dart file to find its dependencies:\n'
+        '  $path\n'
+        '...the analyzer failed with the following error:\n'
+        '  ${error.toString().trimRight()}',
+        error,
+      );
+    }
+  }
+}
+
+class DartDependencyException implements Exception {
+  DartDependencyException(this.message, [this.parent]);
+  final String message;
+  final Exception parent;
+  @override
+  String toString() => message;
 }
\ No newline at end of file

packages/flutter_tools/lib/src/dart/package_map.dart

@@ -48,6 +48,8 @@ class PackageMap {
     final List<String> pathSegments = packageUri.pathSegments.toList();
     final String packageName = pathSegments.removeAt(0);
     final Uri packageBase = map[packageName];
+    if (packageBase == null)
+      return null;
     final String packageRelativePath = fs.path.joinAll(pathSegments);
     return packageBase.resolveUri(fs.path.toUri(packageRelativePath));
   }

packages/flutter_tools/lib/src/run_hot.dart

@@ -5,10 +5,8 @@
 import 'dart:async';
 
 import 'package:meta/meta.dart';
-import 'package:stack_trace/stack_trace.dart';
 
 import 'application_package.dart';
-import 'base/common.dart';
 import 'base/context.dart';
 import 'base/file_system.dart';
 import 'base/logger.dart';
@@ -66,29 +64,6 @@ class HotRunner extends ResidentRunner {
   bool _runningFromSnapshot = true;
   String kernelFilePath;
 
-  @override
-  Future<int> run({
-    Completer<DebugConnectionInfo> connectionInfoCompleter,
-    Completer<Null> appStartedCompleter,
-    String route,
-    bool shouldBuild: true
-  }) {
-    // Don't let uncaught errors kill the process.
-    return Chain.capture(() {
-      return _run(
-        connectionInfoCompleter: connectionInfoCompleter,
-        appStartedCompleter: appStartedCompleter,
-        route: route,
-        shouldBuild: shouldBuild
-      );
-    }, onError: (dynamic error, StackTrace stackTrace) {
-      // Actually exit on ToolExit.
-      if (error is ToolExit)
-        throw error;
-      printError('Exception from flutter run: $error', stackTrace);
-    });
-  }
-
   bool _refreshDartDependencies() {
     if (!hotRunnerConfig.computeDartDependencies) {
       // Disabled.
@@ -102,15 +77,18 @@ class HotRunner extends ResidentRunner {
         new DartDependencySetBuilder(mainPath, packagesFilePath);
     try {
       _dartDependencies = new Set<String>.from(dartDependencySetBuilder.build());
-    } catch (error) {
-      printStatus('Error detected in application source code:', emphasis: true);
-      printError('$error');
+    } on DartDependencyException catch (error) {
+      printError(
+        'Your application could not be compiled, because its dependencies could not be established.\n'
+        '$error'
+      );
       return false;
     }
     return true;
   }
 
-  Future<int> _run({
+  @override
+  Future<int> run({
     Completer<DebugConnectionInfo> connectionInfoCompleter,
     Completer<Null> appStartedCompleter,
     String route,

packages/flutter_tools/test/dart_dependencies_test.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'package:analyzer/analyzer.dart';
 import 'package:flutter_tools/src/dart/dependencies.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:test/test.dart';
@@ -40,9 +39,38 @@ void main()  {
           new DartDependencySetBuilder(mainPath, packagesPath);
       try {
         builder.build();
-        fail('expect an assertion to be thrown.');
-      } on AnalyzerErrorGroup catch (e) {
-        expect(e.toString(), contains('foo.dart: Expected a string literal'));
+        fail('expect an exception to be thrown.');
+      } on DartDependencyException catch (error) {
+        expect(error.toString(), contains('foo.dart: Expected a string literal'));
+      }
+    });
+
+    testUsingContext('bad_path', () {
+      final String testPath = fs.path.join(dataPath, 'bad_path');
+      final String mainPath = fs.path.join(testPath, 'main.dart');
+      final String packagesPath = fs.path.join(testPath, '.packages');
+      final DartDependencySetBuilder builder =
+          new DartDependencySetBuilder(mainPath, packagesPath);
+      try {
+        builder.build();
+        fail('expect an exception to be thrown.');
+      } on DartDependencyException catch (error) {
+        expect(error.toString(), contains('amaze${fs.path.separator}and${fs.path.separator}astonish.dart'));
+      }
+    });
+
+    testUsingContext('bad_package', () {
+      final String testPath = fs.path.join(dataPath, 'bad_package');
+      final String mainPath = fs.path.join(testPath, 'main.dart');
+      final String packagesPath = fs.path.join(testPath, '.packages');
+      final DartDependencySetBuilder builder =
+          new DartDependencySetBuilder(mainPath, packagesPath);
+      try {
+        builder.build();
+        fail('expect an exception to be thrown.');
+      } on DartDependencyException catch (error) {
+        expect(error.toString(), contains('rochambeau'));
+        expect(error.toString(), contains('pubspec.yaml'));
       }
     });
   });

packages/flutter_tools/test/data/dart_dependencies_test/bad_package/.analysis_options

+analyzer:
+  exclude:
+    - '**'

packages/flutter_tools/test/data/dart_dependencies_test/bad_package/.packages

+self:lib/

packages/flutter_tools/test/data/dart_dependencies_test/bad_package/main.dart

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:rochambeau/you_have_your_orders_now_go_man_go.dart';
+

packages/flutter_tools/test/data/dart_dependencies_test/bad_package/pubspec.yaml

+name: self

packages/flutter_tools/test/data/dart_dependencies_test/bad_path/.analysis_options

+analyzer:
+  exclude:
+    - '**'

packages/flutter_tools/test/data/dart_dependencies_test/bad_path/.packages

+self:lib/

packages/flutter_tools/test/data/dart_dependencies_test/bad_path/main.dart

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'amaze/and/astonish.dart';

packages/flutter_tools/test/data/dart_dependencies_test/bad_path/pubspec.yaml

+name: self