RFR: 8276694: Pattern trailing unescaped backslash causes internal error

[Ian Graves]

On Mon, 20 Dec 2021 09:57:14 GMT, Masanori Yano <myano at openjdk.org> wrote:

> Could you please review the 8276694 bug fixes?
> 
> A message specific for this exception should be printed instead of an internal error. This fix adds a new check to output an appropriate exception message when the regular expression ends with an unescaped backslash. This fix also checks the position of the cursor to rule out other syntax errors at the middle position of the regular expression.

Looks good to me. Sponsoring.

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PR: https://git.openjdk.java.net/jdk/pull/6891