Add optional message argument to assert statements in the VM.

runtime/vm/parser.cc

Index: runtime/vm/parser.cc
diff --git a/runtime/vm/parser.cc b/runtime/vm/parser.cc
index d3b62f69fb59dda151d5db756e868abd91a19172..717f9aa2d245934ca6b52b752dd2a5af9fe0dc13 100644
--- a/runtime/vm/parser.cc
+++ b/runtime/vm/parser.cc
@@ -70,6 +70,7 @@ DEFINE_FLAG(bool,
             assert_initializer,
             false,
             "Allow asserts in initializer lists.");
+DEFINE_FLAG(bool, assert_message, false, "Allow message in assert statements");
 
 DECLARE_FLAG(bool, profile_vm);
 DECLARE_FLAG(bool, trace_service);
@@ -9164,6 +9165,10 @@ AstNode* Parser::ParseAssertStatement(bool is_const) {
   const TokenPosition condition_pos = TokenPos();
   if (!I->asserts()) {
     SkipExpr();
+    if (FLAG_assert_message && CurrentToken() == Token::kCOMMA) {
+      ConsumeToken();
+      SkipExpr();
+    }
     ExpectToken(Token::kRPAREN);
     return NULL;
   }
@@ -9173,23 +9178,52 @@ AstNode* Parser::ParseAssertStatement(bool is_const) {
                 "initializer assert expression must be compile time constant.");
   }
   const TokenPosition condition_end = TokenPos();
+  AstNode* message = NULL;
+  TokenPosition message_pos = TokenPosition::kNoSource;
+  if (FLAG_assert_message && CurrentToken() == Token::kCOMMA) {
+    ConsumeToken();
+    message_pos = TokenPos();
+    message = ParseAwaitableExpr(kAllowConst, kConsumeCascades, NULL);
+    if (is_const && !message->IsPotentiallyConst()) {
+      ReportError(
+          message_pos,
+          "initializer assert expression must be compile time constant.");
+    }
+  }
   ExpectToken(Token::kRPAREN);
 
+  if (!is_const) {
+    // Check for being a function if not const.
+    ArgumentListNode* arguments = new (Z) ArgumentListNode(condition_pos);
+    arguments->Add(condition);
+    condition = MakeStaticCall(
+        Symbols::AssertionError(),
+        Library::PrivateCoreLibName(Symbols::CheckAssertion()), arguments);
+  }
+  AstNode* not_condition =
+      new (Z) UnaryOpNode(condition_pos, Token::kNOT, condition);
+
+  // Build call to _AsertionError._throwNew
   ArgumentListNode* arguments = new (Z) ArgumentListNode(condition_pos);
-  arguments->Add(condition);
   arguments->Add(new (Z) LiteralNode(
       condition_pos,
-      Integer::ZoneHandle(Z, Integer::New(condition_pos.value(), Heap::kOld))));
+      Integer::ZoneHandle(Z, Integer::New(condition_pos.Pos()))));
   arguments->Add(new (Z) LiteralNode(
       condition_end,
-      Integer::ZoneHandle(Z, Integer::New(condition_end.value(), Heap::kOld))));
+      Integer::ZoneHandle(Z, Integer::New(condition_end.Pos()))));
+  if (message == NULL) {
+    message = new (Z) LiteralNode(condition_end, Instance::ZoneHandle(Z));
+  }
+  arguments->Add(message);
   AstNode* assert_throw = MakeStaticCall(
       Symbols::AssertionError(),
-      Library::PrivateCoreLibName(is_const ? Symbols::CheckConstAssertion()
-                                           : Symbols::CheckAssertion()),
-      arguments);
+      Library::PrivateCoreLibName(Symbols::ThrowNew()), arguments);
 
-  return assert_throw;
+  return new (Z)
+      IfNode(condition_pos, not_condition,
+             NodeAsSequenceNode((message == NULL) ? condition_pos : message_pos,
+                                assert_throw, NULL),
+             NULL);
 }