[dartdevc] Fix crash when source files contain non-UTF8 characters

* Treat the assertion condition offset as a character offset in the file.
* Allow unrecognized characters to be replaced by a placeholder character. This
  is unrelated to the fix but is just a precautionary measure.

Fixed: 39271
Change-Id: I4871ea41d3a46d26ecac5047265a1dbc1c889350
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/124602
Reviewed-by: Vijay Menon <vsm@google.com>
Commit-Queue: Nicholas Shahan <nshahan@google.com>

Author: nshahan

pkg/dev_compiler/lib/src/kernel/compiler.dart

@@ -3268,10 +3268,11 @@ class ProgramCompiler extends ComputeOnceConstantVisitor<js_ast.Expression>
       jsCondition = runtimeCall('test(#)', [jsCondition]);
     }
 
-    var encodedConditionSource = node
-        .enclosingComponent.uriToSource[node.location.file].source
-        .sublist(node.conditionStartOffset, node.conditionEndOffset);
-    var conditionSource = utf8.decode(encodedConditionSource);
+    var encodedSource =
+        node.enclosingComponent.uriToSource[node.location.file].source;
+    var source = utf8.decode(encodedSource, allowMalformed: true);
+    var conditionSource =
+        source.substring(node.conditionStartOffset, node.conditionEndOffset);
     var location = _toSourceLocation(node.conditionStartOffset);
     return js.statement(' if (!#) #.assertFailed(#, #, #, #, #);', [
       jsCondition,

tests/compiler/dartdevc_native/assertion_failure_message_test.dart

@@ -0,0 +1,29 @@
+// Copyright (c) 2019, 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.
+
+import "utils.dart";
+
+void main() {
+  try {
+    assert(false, "failure message");
+  } on AssertionError catch (error) {
+    var message = error.toString();
+    expectStringContains('Assertion failed:', message);
+    expectStringContains('assertion_failure_message_test.dart:9:12', message);
+    expectStringContains('false', message);
+    expectStringContains('failure message', message);
+  }
+
+  // 失 All offsets and source code extractions should still be correct after
+  // non-UTF8 characters. See: https://github.com/dart-lang/sdk/issues/39271
+  try {
+    assert(false, "after a non-UTF8 character");
+  } on AssertionError catch (error) {
+    var message = error.toString();
+    expectStringContains('Assertion failed:', message);
+    expectStringContains('assertion_failure_message_test.dart:21:12', message);
+    expectStringContains('false', message);
+    expectStringContains('after a non-UTF8 character', message);
+  }
+}

tests/compiler/dartdevc_native/no_such_method_errors_test.dart

@@ -2,14 +2,7 @@
 // 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.
 
-import "package:expect/expect.dart";
-
-_expectInErrorMessage(String expected, String actual) {
-  Expect.isTrue(
-      actual.contains(expected),
-      'Error message should contain "$expected", '
-      'but was ${actual.toString()}.');
-}
+import "utils.dart";
 
 class A {
   int x = 42;
@@ -33,8 +26,8 @@ void main() {
     instanceOfA();
   } on NoSuchMethodError catch (error) {
     var message = error.toString();
-    _expectInErrorMessage("NoSuchMethodError: 'call'", message);
-    _expectInErrorMessage("Receiver: Instance of 'A'", message);
+    expectStringContains("NoSuchMethodError: 'call'", message);
+    expectStringContains("Receiver: Instance of 'A'", message);
   }
 
   dynamic tearOff = instanceOfA.arity1;
@@ -43,52 +36,52 @@ void main() {
     tearOff(1, 2);
   } on NoSuchMethodError catch (error) {
     var message = error.toString();
-    _expectInErrorMessage("NoSuchMethodError: 'bound arity1'", message);
-    _expectInErrorMessage("too many arguments", message);
+    expectStringContains("NoSuchMethodError: 'bound arity1'", message);
+    expectStringContains("too many arguments", message);
   }
 
   // Dynamic call of a class method with too few arguments.
   try {
     tearOff();
   } on NoSuchMethodError catch (error) {
     var message = error.toString();
-    _expectInErrorMessage("NoSuchMethodError: 'bound arity1'", message);
-    _expectInErrorMessage("too few arguments", message);
+    expectStringContains("NoSuchMethodError: 'bound arity1'", message);
+    expectStringContains("too few arguments", message);
   }
 
   // Dynamic call of a top level funciton with too many arguments.
   try {
     dynamicFunction(1, 2);
   } on NoSuchMethodError catch (error) {
     var message = error.toString();
-    _expectInErrorMessage("NoSuchMethodError: 'arity1'", message);
-    _expectInErrorMessage("too many arguments", message);
+    expectStringContains("NoSuchMethodError: 'arity1'", message);
+    expectStringContains("too many arguments", message);
   }
 
   // Dynamic call of a top level funciton with too few arguments.
   try {
     dynamicFunction();
   } on NoSuchMethodError catch (error) {
     var message = error.toString();
-    _expectInErrorMessage("NoSuchMethodError: 'arity1'", message);
-    _expectInErrorMessage("too few arguments", message);
+    expectStringContains("NoSuchMethodError: 'arity1'", message);
+    expectStringContains("too few arguments", message);
   }
 
   // Function.apply() with too many arguments.
   try {
     Function.apply(dynamicFunction, [1, 2]);
   } on NoSuchMethodError catch (error) {
     var message = error.toString();
-    _expectInErrorMessage("NoSuchMethodError: 'arity1'", message);
-    _expectInErrorMessage("too many arguments", message);
+    expectStringContains("NoSuchMethodError: 'arity1'", message);
+    expectStringContains("too many arguments", message);
   }
 
   // Function.apply() with too few arguments.
   try {
     Function.apply(dynamicFunction, []);
   } on NoSuchMethodError catch (error) {
     var message = error.toString();
-    _expectInErrorMessage("NoSuchMethodError: 'arity1'", message);
-    _expectInErrorMessage("too few arguments", message);
+    expectStringContains("NoSuchMethodError: 'arity1'", message);
+    expectStringContains("too few arguments", message);
   }
 }

tests/compiler/dartdevc_native/utils.dart

@@ -0,0 +1,11 @@
+// Copyright (c) 2019, 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.
+
+import "package:expect/expect.dart";
+
+/// Expects that [expected] appears as a substring in [actual].
+expectStringContains(String expected, String actual) {
+  Expect.isTrue(actual.contains(expected),
+      'Failure: "$expected" should appear in: "$actual".');
+}