[ruby-core:106902] [Ruby master Feature#18450] Force break in prettyprint

Issue #18450 has been updated by firasalkhalil (Firas al-Khalil).


mame (Yusuke Endoh) wrote in #note-1:
> Could you explain a use case?

I am writing a code generator where in some cases I need to force-break the output code because it makes more sense for a human reader/reviewer:
Here's an example take directly from my production code:

```
out.nest {
  out.break if code.has_special_condition?
  visitor.process(code[:body])
  # =snip=
}
```

----------------------------------------
Feature #18450: Force break in prettyprint
https://bugs.ruby-lang.org/issues/18450#change-95720

* Author: firasalkhalil (Firas al-Khalil)
* Status: Assigned
* Priority: Normal
* Assignee: akr (Akira Tanaka)
----------------------------------------
# Abstract

Support force-breaking a group in the std's [prettyprint](https://github.com/ruby/prettyprint)

# Background

There is a need to forcibly break a group and transform breakables into
newlines. The library doesn't provide this possibility, directly, through
its public API.

# Proposal

Add a single convenience function to the library's public class `PrettyPrint`

# Implementation

An implementation was submitted to the project's github repository as a 
[pull request](https://github.com/ruby/prettyprint/pull/2).

Here's the patch:

```
diff --git a/lib/prettyprint.rb b/lib/prettyprint.rb
index 188c2e6..1d675a7 100644
--- a/lib/prettyprint.rb
+++ b/lib/prettyprint.rb
@@ -236,6 +236,14 @@ class PrettyPrint
     end
   end

+  # This says "force a line break here".
+  #
+  # It will force the current group's "breakables" to break.
+  def break
+    breakable
+    current_group.break
+  end
+
   # Groups line break hints added in the block. The line break hints are all
   # to be used or not.
   #
diff --git a/test/test_prettyprint.rb b/test/test_prettyprint.rb
index 27e7198..cf889d1 100644
--- a/test/test_prettyprint.rb
+++ b/test/test_prettyprint.rb
@@ -518,4 +518,31 @@ End

 end

+
+class Break < Test::Unit::TestCase # :nodoc:
+  def format()
+    PrettyPrint.format(''.dup) {|q|
+      q.group {
+        q.text 'abc'
+        q.breakable
+        q.text 'def'
+        q.group {
+          q.break
+          q.text 'ghi'
+        }
+        q.breakable
+        q.text 'jkl'
+      }
+    }
+  end
+
+  def test_00_04
+    expected = <<'End'.chomp
+abc def
+ghi jkl
+End
+    assert_equal(expected, format())
+  end
+end
+
```

# Evaluation

It's a simple implementation with no caveats.

# Discussion

Even though it's a simple functionality, and the implementation is straightforward,
getting to this point is not that obvious. This is why it might be helpful for other
users who face such a need.

Indeed, an issue was [opened](https://github.com/ruby/prettyprint/issues/1) not so long ago,
and the proposed solution worked but not quite as expected. The provided implementation
works as expected without tampering with the API's internals, and it's proven in production
environment.

# Summary

This is a feature request for the `prettyprint` library: adding support for _force breaking_
a group. An implementation is provided as both a patch and a PR on github.



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