RFR: 8180276: JTextPane getText return extra when mixed with methods of Document [v5]

[Alexey Ivanov]

On Fri, 8 Apr 2022 12:17:37 GMT, Tejesh R <duke at openjdk.java.net> wrote:

>> getText function returned extra endOfLine when appended. The reason was in `EditorEditorKit` class, `write(Writer out, Document doc, int pos, int len)` method, where translation happens from buffer to Out(Writer Object) if endOfLine is other than '\n' ( which is '\r\n' in windows). In order to write each line till End of line, the string till '\n' is written including '\r' and again endOfLine is written which results in extra Carriage Return. To solve this issue, a Condition is added which checks if previous character to '\n' is '\r', if true then whole string except Carriage Return ('\r') is written, else whole string till before '\n' is written.
>
> Tejesh R has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Updated based on Review Comments

The [`DefaultEditorKit`](https://docs.oracle.com/en/java/javase/17/docs/api/java.desktop/javax/swing/text/DefaultEditorKit.html) class defines handling of new lines: _“…while the document is in memory, the "\n" character is used to define a newline…”_.

[The comment inside its `read` method](https://github.com/openjdk/jdk/blob/096bca4a9c5e8ac2668dd965df92153ea1d80add/src/java.desktop/share/classes/javax/swing/text/DefaultEditorKit.java#L212) explains `\r` is converted to `\n` upon reading.

As such, the behaviour described in [JDK-8180276](https://bugs.openjdk.java.net/browse/JDK-8180276) is not a bug. The mistake is that the user uses `System.lineSeparator()` to add a line break to the document model. Since it's the model, `\n` is to be used, which is _system-independent_. When document is written to disk, line breaks are converted to system-dependent according to the value of [`EndOfLineStringProperty`](https://docs.oracle.com/en/java/javase/17/docs/api/java.desktop/javax/swing/text/DefaultEditorKit.html#EndOfLineStringProperty) property of the document.

If we handle `\r` before `\n` when writing out a document, we may get another bug report where `\r` not followed by `\n` results in a line break too. This is why I consider the current behaviour correct. The questions by @prsadhuk and the resulted discussion have led me to this conclusion.

The bug should be closed as *Not an Issue* with the explanation that `\n` should always be used to add line break in a `Document` model, `System.lineSeparator()` should not be used.

Does it sound reasonable?

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PR: https://git.openjdk.java.net/jdk/pull/8122