RFR: 8259050: Error recovery in lexer could be improved

[Jan Lahoda]

Consider code like:
public class BrokenEscape {
    private String s = "\uaaa";
}
(note the broken escape). This produces:
$ javac BrokenEscape.java 
BrokenEscape.java:2: error: illegal unicode escape
    private String s = "\uaaa";
                        ^
BrokenEscape.java:2: error: unclosed string literal
    private String s = "\uaaa";
                       ^
2 errors

After this patch, it produces:
$ javac BrokenEscape.java 
BrokenEscape.java:2: error: illegal unicode escape
    private String s = "\uaaa";
                             ^
1 error
which is the error message that used to be produced in the past.

The patch also improves the AST for source levels where text blocks are not supported, but are in fact present in the source code.

-------------

Commit messages:
 - 8259050: Error recovery in lexer could be improved

Changes: https://git.openjdk.java.net/jdk/pull/2239/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2239&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8259050
  Stats: 91 lines in 4 files changed: 79 ins; 0 del; 12 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2239.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2239/head:pull/2239

PR: https://git.openjdk.java.net/jdk/pull/2239