AST structure is modified after being passed to listeners

[bwilkerson]

We need to have a contract that the AST structure passed in to DartCompilerListener.unitCompiled(DartUnit) will not subsequently be modified because clients (such as Editor) need to be able to count on the structure remaining stable. This is currently not the case, which is causing a ConcurrentModificationException to be thrown while attempting to index the structure.

I found one place where the structure can be modified after it is passed to clients: the method com.google.dart.compiler.backend.js.Normalizer.NormalizerVisitor.Let.visitClass(DartClass) adds a node for the implicit default constructor (assuming there is one) to the list of members in a class. There might be other places, but I decided not to try to track them down. The only other place I found where the DartClass.members list might be modified is through the method DartClass.traverse(DartVisitor, DartContext), which implies that the list can be modified by visitors, but I didn't try to trace through all of the visitors to see whether the list is actually modified by any of them. I didn't even look at other lists (this is the one that caused the exception).

[scheglov]

Set owner to @scheglov.
Added Accepted label.

[scheglov]

Marked this as being blocked by #590.

[DartBot]

This comment was originally written by zundel@google.com

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The normalizer and all other backend stuff has been removed from dartc.

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Added AssumedStale label.