JDK-8227870 - Escape Sequences For Line Continuation and White Space (Preview)

[John Rose]

On Sep 30, 2019, at 4:45 AM, Jim Laskey <james.laskey at oracle.com> wrote:
> 
> During the discussion on Text Blocks, several of you stated a need for a line continuation construct. I have since created a CSR to propose the creation of two new escape sequences: \<line terminator> and \s.
> 
> 	https://bugs.openjdk.java.net/browse/JDK-8227870
> 

One observation:  Some traditional uses of \LT, as in C macros, makefiles, and shell,
line up the \ characters in a single column as a sort of right-hand fence:

   foo bar     \
     baz        \
       bat

This can be done only in settings where the spaces before the \ are treated as
ancillary format, not payload characters.  We could make a similar rule for multi-line
literals, by saying that unescaped spaces *before* the \LT are also deleted when
the \LT sequence is deleted.

In other words, the \ at the end of the line is *not* a fence that transforms the 

So:

var x = “””
   foo bar     \
     baz        \
       bat      \
  “””;
assert x.equals(“foo bar baz   bat”);

The single space before baz and the three spaces before bat are the left-hand
leading spaces, not the ancillary spaces before the \ characters.

If some of those trailing spaces are desirable, then \s can be used to make
a fence that saves them from stripping.

var x = “””
   foo bar\s   \
   baz  \s      \
   bat\s         \
  “””;
assert x.equals(“foo bar baz   bat ”);

This rule decouples the two functions of \LT in the current proposal:  (1) It joins
lines, and (2) it creates a fence which makes previously ancillary spaces into
real payload spaces.  These are distinct jobs and should not be conflated.
I think it’s a small but real improvement to separate the jobs, and allow \s
to handle (2) and \LT to handle only (1).

— John

P.S.  A variation of the above suggestion, probably less preferable, would delete
spaces both *before* and *after* \LT, leading to this:

var x = “””
   foo bar     \
     baz        \
       bat      \
  “””;
assert x.equals(“foo barbazbat”);

Again, \s could save spaces from stripping.