Support Text Blocks (JEP 368)

[sormuras]

A text block is a multi-line string literal that avoids the need for most escape sequences, automatically formats the string in a predictable way, and gives the developer control over format when desired. This is a preview language feature in JDK 13.

Syntax and more details at https://openjdk.java.net/jeps/355 https://openjdk.java.net/jeps/368

Formatting a Java source file...
java -jar google-java-format-1.7-all-deps.jar TextBlock.java

...that contains Text Blocks...

public class TextBlock {
  public static void main(String... args) {
    var block = """

    java --enable-preview --s\\o/urce 14 TextBlock.java
    openjdk                   |              -|-
    14-ea                     /\\  o           /\\
    2020-03-17
    """.indent(6);

    System.out.print(block);
  }
}

...fails with:

TextBlock.java:3:20: error: unclosed string literal
TextBlock.java:5:13: error: ';' expected
TextBlock.java:5:19: error: not a statement
TextBlock.java:5:30: error: ';' expected
TextBlock.java:5:31: error: illegal character: '\'
TextBlock.java:5:32: error: illegal character: '\'
TextBlock.java:5:34: error: not a statement
TextBlock.java:5:39: error: ';' expected
TextBlock.java:6:13: error: ';' expected
TextBlock.java:7:33: error: illegal character: '\'
TextBlock.java:7:32: error: not a statement
TextBlock.java:7:34: error: illegal character: '\'
TextBlock.java:7:50: error: illegal character: '\'
TextBlock.java:7:49: error: not a statement
TextBlock.java:7:51: error: illegal character: '\'
TextBlock.java:9:8: error: unclosed string literal

[sormuras]

Some errors are reported when calling java with --enable-preview. Seems like that option isn't passed to the internal javac instance, methinks.

[sormuras]

Or is error-prone not there, yet?

google-java-format/pom.xml

Line 99 in 0a449a5

<javac.version>9+181-r4173-1</javac.version>

[sormuras]

How about omit Text Blocks entirely from formatting?

[talios]

@sormuras if existing formatting changes the indent position of the start of the block, GJF should reindent the text block to preserve the gray-space eliding by the compiler. Reformatting shouldn't break tests, which that may.

[sormuras]

if existing formatting changes [...]

Lines contributing to a """-String literal shouldn't be touched at all - as an initial work-around.

[sormuras]

if existing formatting changes the indent position of the start of the block, [...]

IIRC, the position of the start """ does not influence the white-space trim. The terminating """ does.

See https://blog.codefx.org/java/text-blocks/ (as jdk.java.net doesn't work at the moment)

[sormuras]

Second Preview of Text Blocks issued: https://openjdk.java.net/jeps/368

New escape sequences
To allow finer control of the processing of newlines and white space, text blocks support two additional escape sequences not available in ordinary string literals.
First, the \<line-terminator> escape sequence explicitly suppresses the insertion of a newline character.
...
Second, the \s escape sequence simply translates to a single space (\u0020).
...

Updated issue title accordingly.

[cushon]

#436