Debugger no longer causes top level variable initialization

Debugger no longer causes top level variable initialization

When a top-level variable has not been initialized yet, the
debugger reports a value of ‘null’ rather than causing a side
effect of running the initializer code.

R=jacobr@google.com, srdjan@google.com

Committed: https://code.google.com/p/dart/source/detail?r=31678

[hausner, 2014-01-09 17:44:11]

Ping

[Jacob, 2014-01-09 17:51:11]

https://codereview.chromium.org/126653003/diff/1/runtime/vm/debugger.cc
File runtime/vm/debugger.cc (right):

https://codereview.chromium.org/126653003/diff/1/runtime/vm/debugger.cc#newco...
runtime/vm/debugger.cc:1821: // If the field is not initialized yet, just report
the value
At what times will this occur?
It seems confusing for a user to see a static field with a value of null even
though it is initialized to a non-null value

E.g. 
class Pen {
  static DASHED = new LineStyle("dashed");
  static DOTTED = new LineStyle("dotted");
}

[hausner, 2014-01-09 17:55:21]

This will occur when the debugger displays the value of a top-level variable
before the program actually referenced the variable and caused the initializer
expression to run.

I agree that this is confusing, but this is in the vein of the debugger not
causing side effects in the debug target.

A better solution would be to have a dedicated null value that means
"uninitialized" exported by the Dart API. But that's a bigger change.

[Jacob, 2014-01-09 18:05:09]

On 2014/01/09 17:55:21, hausner wrote:
> This will occur when the debugger displays the value of a top-level variable
> before the program actually referenced the variable and caused the initializer
> expression to run.
> 
> I agree that this is confusing, but this is in the vein of the debugger not
> causing side effects in the debug target.
> 
> A better solution would be to have a dedicated null value that means
> "uninitialized" exported by the Dart API. But that's a bigger change.

Is there a bug tracking that change? We will need it at some point.
I assume if that if I invoke a static as a getter the value will be initialized
but I need to know that the value is not initialized to begin with.

[srdjan, 2014-01-09 18:15:32]

https://codereview.chromium.org/126653003/diff/1/runtime/vm/debugger.cc
File runtime/vm/debugger.cc (right):

https://codereview.chromium.org/126653003/diff/1/runtime/vm/debugger.cc#newco...
runtime/vm/debugger.cc:1825: field_value = Object::null();
Can we use a value like 'optimized out', or in this case 'uninitialized'.

[hausner, 2014-01-09 21:23:12]

PTAL. I am using the symbol <uninitialized> now to indicate that the variable
has not been initialized yet.

[Jacob, 2014-01-09 21:34:44]

lgtm

[srdjan, 2014-01-09 21:39:22]

lgtm

[Jakob.Gruber, 2014-01-09 21:46:38]

https://codereview.chromium.org/126653003/diff/100001/runtime/vm/debugger.cc
File runtime/vm/debugger.cc (right):

https://codereview.chromium.org/126653003/diff/100001/runtime/vm/debugger.cc#...
runtime/vm/debugger.cc:1822: // to be null. We don't want to execute the
implicit getter
The comment now refers to null while the value is actually set to Uninitialized.

[hausner, 2014-01-09 21:50:04]

Nice catch by Jakob. Also changed the special value to <not initialized> to
match what vmservice uses.

https://codereview.chromium.org/126653003/diff/100001/runtime/vm/debugger.cc
File runtime/vm/debugger.cc (right):

https://codereview.chromium.org/126653003/diff/100001/runtime/vm/debugger.cc#...
runtime/vm/debugger.cc:1822: // to be null. We don't want to execute the
implicit getter
On 2014/01/09 21:46:38, Jakob.Gruber wrote:
> The comment now refers to null while the value is actually set to
Uninitialized.

Nice catch, thank you.

[hausner, 2014-01-09 21:50:25]

Committed patchset #5 manually as r31678 (presubmit successful).