Declaring variable with same name as existing variable should be an error

[DartBot]

This issue was originally filed by domi...@google.com

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1 void OverrideParameter(int s) {
2 String s = '42';
3 write(s);
4
5 double s = 42.0;
6 }

There should be errors at lines 2 and 5 where variables are being declared with the same names as existing variables in scope.

This can lead to very subtle bugs and although they might be caught when the variables are used, it would be better to flag the error early.

[DartBot]

This comment was originally written by drfibonacci@google.com

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Added Area-Editor, Triaged labels.

[devoncarew]

I can't reproduce this. Using the latest version of the editor I get this error: "duplicate definition of s" on line 5 of your example. Are you compiling with the editor / dartc or with frog?

[DartBot]

This comment was originally written by domi...@google.com

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Editor, the latest. I tried both incremental and full rebuild.

In the original example of which this is a cut down version, the file
definitely compiled. The warning I received was as the point the object was
passed to a method which expected a different type.

[devoncarew]

Ok, it sounds like the original file exhibited this name-masking bug, and the snippet does not. Can you include more of the original file in order for us to reproduce the problem?

Bumping this over to the dartc team for them to take a look at.

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Removed Area-Editor label.
Added Area-Compiler label.

[scheglov]

Are you sure that re-declaring variable is error?
I don't see anything about this in spec, 11.3 Variable Declaration.
Quite opposite - it says "Executing a variable declaration statement T id = e; is equivalent to evaluating the assignment expression id = e". I interpret this as permission to re-define variable, because you can have as much "id = e" as you want.

[scheglov]

http://codereview.chromium.org/8966029

[scheglov]

We've added many errors and warnings for re-declaring variables and hiding names.

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Added Fixed label.