Put the caret on the right side of the composition string

Put the caret on the right side of the composition string

On Windows, when a user writes sentences in Korean, we put the caret on the left
side of the composition string, but this behavior is exactly opposite to that of
other environments. This CL ensures that the caret is always positioned at the
right side of the composition string on all environments for consistency.

BUG=653160

[Sungmann Cho, 2017-04-13 07:44:40]

sungmann.cho@navercorp.com changed reviewers:
+ yukawa@chromium.org

[Sungmann Cho, 2017-04-13 07:44:41]

Please take a look. Thanks!

[Sungmann Cho, 2017-04-17 02:05:35]

ping...

[yukawa, 2017-04-17 03:01:05]

yukawa@chromium.org changed reviewers:
+ shuchen@chromium.org, suzhe@chromium.org

[yukawa, 2017-04-17 03:01:06]

Thank you for the patch.

My concern of making this change is that even if it addresses crbug.com/653160,
mechanically replacing |0| with |length| could introduce yet another different
problem for other languages / other IMEs.  Shouldn't we minimize the condition
to set |length| so that only MS-IME Korean can be addressed?

Can you check what lparam is specified by MS-IME Korean?

Also please get OK from suzhe@, who wrote that code.

https://codereview.chromium.org/2816683004/diff/1/ui/base/ime/win/imm32_manag...
File ui/base/ime/win/imm32_manager.cc (right):

https://codereview.chromium.org/2816683004/diff/1/ui/base/ime/win/imm32_manag...
ui/base/ime/win/imm32_manager.cc:310: // the beginning of the composition
string. Otherwise we should honour the
"we just place the caret at the beginning of the composition string"

Are you sure that CS_NOMOVECARET is specified in this case?  With you change,
now the comment becomes inconsistent with the actual behavior.

[yukawa, 2017-04-17 04:12:00]

https://codereview.chromium.org/2816683004/diff/1/ui/base/ime/win/imm32_manag...
File ui/base/ime/win/imm32_manager.cc (right):

https://codereview.chromium.org/2816683004/diff/1/ui/base/ime/win/imm32_manag...
ui/base/ime/win/imm32_manager.cc:314: if (!(lparam & CS_NOMOVECARET) && (lparam
& GCS_CURSORPOS)) {
As far as I've tested with the stock MS-IME Korean on Windows 7 SP1, the
following flags are specified in |lparam|.
 - GCS_COMPATTR
 - GCS_COMPSTR
 - CS_NOMOVECARET
 - CS_INSERTCHAR

https://msdn.microsoft.com/en-us/library/windows/desktop/dd374133.aspx

Here is the important part:
  CS_NOMOVECARET:
    Do not move the caret position as a result of processing the
    message. For example, if an IME specifies a combination of
    CS_INSERTCHAR and CS_NOMOVECARET, the application should insert
    the specified character at the current caret position but should
    not move the caret to the next position. A subsequent
    WM_IME_COMPOSITION message with GCS_RESULTSTR will replace this
    character.

So as far as the API spec is concerned, I think the current Chromium's code
actually makes sense because those flags are intentionally specified by MS-IME
Korean (or Cicero Unaware Application Support).

I don't say that we should give up to fix crbug.com/653160, but if we would
decide to violate the spec requested by the API intentionally, we should try to
minimize the impact so as not to break other IMEs that expect Chromium to
support these flags correctly.