[kernel] Fix assert message.

pkg/front_end/lib/src/fasta/kernel/body_builder.dart

Index: pkg/front_end/lib/src/fasta/kernel/body_builder.dart
diff --git a/pkg/front_end/lib/src/fasta/kernel/body_builder.dart b/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
index 3d17400b0046cd784ac662092a11eb7d31bc67db..e39b1e2ebaf14ce2d396c662d1b761c159300141 100644
--- a/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
@@ -2658,6 +2658,10 @@ class BodyBuilder extends ScopeListener<JumpTarget> implements BuilderHelper {
     Expression message = popForValueIfNotNull(commaToken);
     Expression condition = popForValue();
     AssertStatement statement = new AssertStatement(condition, message);
+    statement.conditionStartOffset = leftParenthesis.next.offset;
+    Token lastTokenInCondition = rightParenthesis.previous;

[ahe, 2017/06/16 07:39:42]

We want to get rid of "previous". Could you do something like this instead:

Token lastTokenInCondition = leftParenthesis;
while (lastTokenInCondition.next != rightParenthesis) {
  lastTokenInCondition = lastTokenInCondition.next;
}

Or:

Token lastTokenInCondition = rightParenthesis.offset - 1;

[jensj, 2017/06/16 07:43:29]

I could. But:
1) I suppose an assert can be arbitrarily long so that could potentially be
slow.
2) This could theoretically include a lot of linebreaks and whatnot at the end,
when we want to extract the source code between the start and the end. It might
not be a big deal through, I'm not sure.

What do you think?

[ahe, 2017/06/16 07:53:35]

statement.conditionStartOffset = leftParenthesis.offset + 1;
statement.conditionEndOffset = rightParenthesis.offset - 1;

This way, you also get any comments included, and line breaks could easily be
removed with a call to "trim()" in runtime/lib/errors_patch.dart.

[jensj, 2017/06/16 09:28:25]

Actually not -1 on the end as that would could off the last char.

+    statement.conditionEndOffset =
+        lastTokenInCondition.offset + lastTokenInCondition.length;
     switch (kind) {
       case Assert.Statement:
         push(statement);