Make Scanner::kNoSourcePos be a true sentinel value

Make Scanner::kNoSourcePos be a true sentinel value

- It is possible to write a Dart program with a function token_pos of 0.
- Switch Scanner::kNoSourcePos from 0 to -1.

R=hausner@google.com

Committed: https://github.com/dart-lang/sdk/commit/cb8b641cc9a0da1ef4460d57b21c21e48455f1dd

[Cutch, 2016-01-05 22:03:51]

Description was changed from

==========
Make Scanner::kNoSourcePos be a true sentinel value

BUG=
==========

to

==========
Make Scanner::kNoSourcePos be a true sentinel value

- It is possible to write a Dart program with a token_pos of 0.
- Switch Scanner::kNoSourcePos from 0 to -1.
==========

[Cutch, 2016-01-05 22:03:51]

johnmccutchan@google.com changed reviewers:
+ hausner@google.com, rmacnak@google.com

[hausner, 2016-01-05 22:30:50]

LGTM with comments.

https://codereview.chromium.org/1564493002/diff/1/runtime/vm/object.cc
File runtime/vm/object.cc (right):

https://codereview.chromium.org/1564493002/diff/1/runtime/vm/object.cc#newcod...
runtime/vm/object.cc:3452: ASSERT(Scanner::ValidSourcePosition(token_pos));
Can there be classes with kNoSourcePos?
Ditto for the other setters below.

https://codereview.chromium.org/1564493002/diff/1/runtime/vm/scanner.h
File runtime/vm/scanner.h (right):

https://codereview.chromium.org/1564493002/diff/1/runtime/vm/scanner.h#newcode50
runtime/vm/scanner.h:50: static bool ValidSourcePosition(intptr_t token_pos) {
I'd expect ValidSourcePosition() to check whether it is indeed a value that
represents a position, which does not include kNoSourcePos. Maybe this function
is not needed. We only use it in ASSERTS it seems. Just get rid of those
asserts?

[Cutch, 2016-01-06 15:42:03]

Description was changed from

==========
Make Scanner::kNoSourcePos be a true sentinel value

- It is possible to write a Dart program with a token_pos of 0.
- Switch Scanner::kNoSourcePos from 0 to -1.
==========

to

==========
Make Scanner::kNoSourcePos be a true sentinel value

- It is possible to write a Dart program with a function token_pos of 0.
- Switch Scanner::kNoSourcePos from 0 to -1.
==========

[Cutch, 2016-01-06 15:42:19]

https://codereview.chromium.org/1564493002/diff/1/runtime/vm/object.cc
File runtime/vm/object.cc (right):

https://codereview.chromium.org/1564493002/diff/1/runtime/vm/object.cc#newcod...
runtime/vm/object.cc:3452: ASSERT(Scanner::ValidSourcePosition(token_pos));
On 2016/01/05 22:30:50, hausner wrote:
> Can there be classes with kNoSourcePos?
> Ditto for the other setters below.

When first being constructed (Class::New) we set it to Scanner::kNoSourcePos.
Similarly for other objects.

https://codereview.chromium.org/1564493002/diff/1/runtime/vm/scanner.h
File runtime/vm/scanner.h (right):

https://codereview.chromium.org/1564493002/diff/1/runtime/vm/scanner.h#newcode50
runtime/vm/scanner.h:50: static bool ValidSourcePosition(intptr_t token_pos) {
On 2016/01/05 22:30:50, hausner wrote:
> I'd expect ValidSourcePosition() to check whether it is indeed a value that
> represents a position, which does not include kNoSourcePos. Maybe this
function
> is not needed. We only use it in ASSERTS it seems. Just get rid of those
> asserts? 

Maybe I should rename the function to be clearer. I considered removing the
ASSERTs too but then I thought that it might be nice to make sure that we never
set a token position that isn't >= 0 or equal to the sentinel value.

[Cutch, 2016-01-06 17:06:32]

Description was changed from

==========
Make Scanner::kNoSourcePos be a true sentinel value

- It is possible to write a Dart program with a function token_pos of 0.
- Switch Scanner::kNoSourcePos from 0 to -1.
==========

to

==========
Make Scanner::kNoSourcePos be a true sentinel value

- It is possible to write a Dart program with a function token_pos of 0.
- Switch Scanner::kNoSourcePos from 0 to -1.

R=hausner@google.com

Committed:
https://github.com/dart-lang/sdk/commit/cb8b641cc9a0da1ef4460d57b21c21e48455f1dd
==========

[Cutch, 2016-01-06 17:06:33]

Committed patchset #4 (id:60001) manually as
cb8b641cc9a0da1ef4460d57b21c21e48455f1dd (presubmit successful).