Clarify that when a local variable hides a type before it is declared, it is stilla compile-time er…

Clarify that when a local variable hides a type before it is declared, it is stilla compile-time error, and that the VM has flexibility to report such errors at the declaration rather than the use.

R=hausner@google.com

Committed: https://code.google.com/p/dart/source/detail?r=28896

[hausner, 2013-10-18 23:09:23]

LGTM.

https://codereview.chromium.org/30123002/diff/1/docs/language/dartLangSpec.tex
File docs/language/dartLangSpec.tex (right):

https://codereview.chromium.org/30123002/diff/1/docs/language/dartLangSpec.te...
docs/language/dartLangSpec.tex:821: We allow the error to be reported at the
declaration to allow implementations to avoid an extra processing phase.
True. But it is more important that the error is a compile-time error (vs.
runtime error) than where it is reported. The compiler can easily remember where
a name is first used and report the error there. However, if "reference before
declaration" is a runtime error, we would have to go back and potentially patch
all uses of the name if a shadowing declaration is found later.

[gbracha, 2013-10-18 23:12:01]

Committed patchset #2 manually as r28896 (presubmit successful).