From 3e62945b8a18237dfe0828a945df04630349d892 Mon Sep 17 00:00:00 2001
From: Mateusz Samsel <m.samsel@cksource.com>
Date: Mon, 27 May 2019 12:19:38 +0200
Subject: [PATCH 01/10] Add support for preserving text attributes on enter.

---
 src/entercommand.js   | 11 +++++++++++
 tests/entercommand.js | 25 +++++++++++++++++++++++++
 2 files changed, 36 insertions(+)

diff --git a/src/entercommand.js b/src/entercommand.js
index db5478b..5de5f78 100644
--- a/src/entercommand.js
+++ b/src/entercommand.js
@@ -56,7 +56,10 @@ function enterBlock( model, writer, selection, schema ) {
 	}
 
 	if ( isSelectionEmpty ) {
+		// List of text attributes copied to new line/block.
+		const filteredAttr = getAllowedAttributes( writer.model.schema, selection.getAttributes() );
 		splitBlock( writer, range.start );
+		writer.setSelectionAttribute( filteredAttr );
 	} else {
 		const leaveUnmerged = !( range.start.isAtStart && range.end.isAtEnd );
 		const isContainedWithinOneElement = ( startElement == endElement );
@@ -84,3 +87,11 @@ function splitBlock( writer, splitPos ) {
 	writer.split( splitPos );
 	writer.setSelection( splitPos.parent.nextSibling, 0 );
 }
+
+function* getAllowedAttributes( schema, allAttributes ) {
+	for ( const attr of allAttributes ) {
+		if ( attr && schema.getAttributeProperties( attr[ 0 ] ).copyOnEnter ) {
+			yield attr;
+		}
+	}
+}
diff --git a/tests/entercommand.js b/tests/entercommand.js
index d8e7217..dedd381 100644
--- a/tests/entercommand.js
+++ b/tests/entercommand.js
@@ -87,6 +87,31 @@ describe( 'EnterCommand', () => {
 				'<p>x</p><p>[]</p><p>y</p>',
 				'<p>x</p><p></p><p>[]</p><p>y</p>'
 			);
+
+			describe( 'copyOnEnter', () => {
+				beforeEach( () => {
+					schema.extend( '$text', { allowAttributes: 'foo' } );
+					schema.setAttributeProperties( 'foo', { copyOnEnter: true } );
+				} );
+
+				test(
+					'allowed attributes are copied',
+					'<p><$text foo="true">test[]</$text></p>',
+					'<p><$text foo="true">test</$text></p><p selection:foo="true"><$text foo="true">[]</$text></p>'
+				);
+
+				test(
+					'unknown attributes are disabled',
+					'<p><$text bar="true">test[]</$text></p>',
+					'<p><$text bar="true">test</$text></p><p>[]</p>'
+				);
+
+				test(
+					'only allowed attributes are copied from mix set',
+					'<p><$text bar="true" foo="true">test[]</$text></p>',
+					'<p><$text bar="true" foo="true">test</$text></p><p selection:foo="true"><$text foo="true">[]</$text></p>'
+				);
+			} );
 		} );
 
 		describe( 'non-collapsed selection', () => {

From 66d211f2e2b69cd85d5d4925d7a247524e601362 Mon Sep 17 00:00:00 2001
From: Mateusz Samsel <msamsel@users.noreply.github.com>
Date: Mon, 1 Jul 2019 10:46:55 +0200
Subject: [PATCH 02/10] Apply suggestions from code review

Co-Authored-By: Maciej <jodator@gmail.com>
---
 tests/entercommand.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tests/entercommand.js b/tests/entercommand.js
index dedd381..092b33d 100644
--- a/tests/entercommand.js
+++ b/tests/entercommand.js
@@ -101,7 +101,7 @@ describe( 'EnterCommand', () => {
 				);
 
 				test(
-					'unknown attributes are disabled',
+					'unknown attributes are not copied',
 					'<p><$text bar="true">test[]</$text></p>',
 					'<p><$text bar="true">test</$text></p><p>[]</p>'
 				);

From 753ea20108eb5d991734d5cce07112784447ca7f Mon Sep 17 00:00:00 2001
From: Mateusz Samsel <m.samsel@cksource.com>
Date: Mon, 1 Jul 2019 11:02:09 +0200
Subject: [PATCH 03/10] Improve name of variables used in code.

---
 src/entercommand.js   | 13 ++++++-------
 tests/entercommand.js |  2 +-
 2 files changed, 7 insertions(+), 8 deletions(-)

diff --git a/src/entercommand.js b/src/entercommand.js
index 5de5f78..0be8303 100644
--- a/src/entercommand.js
+++ b/src/entercommand.js
@@ -56,10 +56,9 @@ function enterBlock( model, writer, selection, schema ) {
 	}
 
 	if ( isSelectionEmpty ) {
-		// List of text attributes copied to new line/block.
-		const filteredAttr = getAllowedAttributes( writer.model.schema, selection.getAttributes() );
+		const attributesToCopy = getCopyOnEnterAttributes( writer.model.schema, selection.getAttributes() );
 		splitBlock( writer, range.start );
-		writer.setSelectionAttribute( filteredAttr );
+		writer.setSelectionAttribute( attributesToCopy );
 	} else {
 		const leaveUnmerged = !( range.start.isAtStart && range.end.isAtEnd );
 		const isContainedWithinOneElement = ( startElement == endElement );
@@ -88,10 +87,10 @@ function splitBlock( writer, splitPos ) {
 	writer.setSelection( splitPos.parent.nextSibling, 0 );
 }
 
-function* getAllowedAttributes( schema, allAttributes ) {
-	for ( const attr of allAttributes ) {
-		if ( attr && schema.getAttributeProperties( attr[ 0 ] ).copyOnEnter ) {
-			yield attr;
+function* getCopyOnEnterAttributes( schema, allAttributes ) {
+	for ( const attribute of allAttributes ) {
+		if ( attribute && schema.getAttributeProperties( attribute[ 0 ] ).copyOnEnter ) {
+			yield attribute;
 		}
 	}
 }
diff --git a/tests/entercommand.js b/tests/entercommand.js
index 092b33d..3d5f52c 100644
--- a/tests/entercommand.js
+++ b/tests/entercommand.js
@@ -90,7 +90,7 @@ describe( 'EnterCommand', () => {
 
 			describe( 'copyOnEnter', () => {
 				beforeEach( () => {
-					schema.extend( '$text', { allowAttributes: 'foo' } );
+					schema.extend( '$text', { allowAttributes: [ 'foo', 'bar' ] } );
 					schema.setAttributeProperties( 'foo', { copyOnEnter: true } );
 				} );
 

From 13f994546efdb360adf94034346e9118b2c718b1 Mon Sep 17 00:00:00 2001
From: Mateusz Samsel <m.samsel@cksource.com>
Date: Thu, 11 Jul 2019 16:32:42 +0200
Subject: [PATCH 04/10] Add support for copyOnEnter for shiftenter command.

---
 src/entercommand.js      |  9 +--------
 src/shiftentercommand.js |  3 +++
 src/utils.js             | 25 +++++++++++++++++++++++++
 3 files changed, 29 insertions(+), 8 deletions(-)
 create mode 100644 src/utils.js

diff --git a/src/entercommand.js b/src/entercommand.js
index 0be8303..b267717 100644
--- a/src/entercommand.js
+++ b/src/entercommand.js
@@ -8,6 +8,7 @@
  */
 
 import Command from '@ckeditor/ckeditor5-core/src/command';
+import { getCopyOnEnterAttributes } from './utils';
 
 /**
  * Enter command. It is used by the {@link module:enter/enter~Enter Enter feature} to handle the <kbd>Enter</kbd> key.
@@ -86,11 +87,3 @@ function splitBlock( writer, splitPos ) {
 	writer.split( splitPos );
 	writer.setSelection( splitPos.parent.nextSibling, 0 );
 }
-
-function* getCopyOnEnterAttributes( schema, allAttributes ) {
-	for ( const attribute of allAttributes ) {
-		if ( attribute && schema.getAttributeProperties( attribute[ 0 ] ).copyOnEnter ) {
-			yield attribute;
-		}
-	}
-}
diff --git a/src/shiftentercommand.js b/src/shiftentercommand.js
index 5944238..0dd83c5 100644
--- a/src/shiftentercommand.js
+++ b/src/shiftentercommand.js
@@ -8,6 +8,7 @@
  */
 
 import Command from '@ckeditor/ckeditor5-core/src/command';
+import { getCopyOnEnterAttributes } from './utils';
 
 /**
  * ShiftEnter command. It is used by the {@link module:enter/shiftenter~ShiftEnter ShiftEnter feature} to handle
@@ -81,7 +82,9 @@ function softBreakAction( model, writer, selection ) {
 	const isContainedWithinOneElement = ( startElement == endElement );
 
 	if ( isSelectionEmpty ) {
+		const attributesToCopy = getCopyOnEnterAttributes( model.schema, selection.getAttributes() );
 		insertBreak( writer, range.end );
+		writer.setSelectionAttribute( attributesToCopy );
 	} else {
 		const leaveUnmerged = !( range.start.isAtStart && range.end.isAtEnd );
 		model.deleteContent( selection, { leaveUnmerged } );
diff --git a/src/utils.js b/src/utils.js
new file mode 100644
index 0000000..f428c7c
--- /dev/null
+++ b/src/utils.js
@@ -0,0 +1,25 @@
+/**
+ * @license Copyright (c) 2003-2019, CKSource - Frederico Knabben. All rights reserved.
+ * For licensing, see LICENSE.md or https://ckeditor.com/legal/ckeditor-oss-license
+ */
+
+/**
+ * @module enter/utils
+ */
+
+/**
+ * Returns iterator which has filtered attributes read from {@link module:engine/model/selection~Selection#getAttributes selection}.
+ * Filtering is realized based on `copyOnEnter` attribute property. Read more about attribute properties
+ * {@link module:engine/model/schema~Schema#setAttributeProperties here}.
+ *
+ * @param {module:engine/model/schema~Schema} schema
+ * @param {Iterable.<*>} allAttributes iterator with attributes of current selection.
+ * @returns {Iterable.<*>} filtered attributes which has `copyOnEnter` property.
+ */
+export function* getCopyOnEnterAttributes( schema, allAttributes ) {
+	for ( const attribute of allAttributes ) {
+		if ( attribute && schema.getAttributeProperties( attribute[ 0 ] ).copyOnEnter ) {
+			yield attribute;
+		}
+	}
+}

From c0c23c2fae98edf3536b0bb2345b7e58d7dbc908 Mon Sep 17 00:00:00 2001
From: Mateusz Samsel <m.samsel@cksource.com>
Date: Thu, 11 Jul 2019 17:06:43 +0200
Subject: [PATCH 05/10] Add unit test for util generator.

---
 tests/utils.js | 38 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)
 create mode 100644 tests/utils.js

diff --git a/tests/utils.js b/tests/utils.js
new file mode 100644
index 0000000..37cb4cb
--- /dev/null
+++ b/tests/utils.js
@@ -0,0 +1,38 @@
+/**
+ * @license Copyright (c) 2003-2019, CKSource - Frederico Knabben. All rights reserved.
+ * For licensing, see LICENSE.md or https://ckeditor.com/legal/ckeditor-oss-license
+ */
+
+import { getCopyOnEnterAttributes } from '../src/utils';
+import ModelTestEditor from '@ckeditor/ckeditor5-core/tests/_utils/modeltesteditor';
+
+describe( 'utils', () => {
+	describe( 'getCopyOnEnterAttributes()', () => {
+		it( 'filters attributes with copyOnEnter property', () => {
+			return ModelTestEditor.create()
+				.then( editor => {
+					const schema = editor.model.schema;
+
+					schema.register( 'foo', { inheritAllFrom: '$block' } );
+					schema.register( 'bar', { inheritAllFrom: '$block' } );
+					schema.register( 'baz', { inheritAllFrom: '$block' } );
+
+					schema.setAttributeProperties( 'foo', { copyOnEnter: true } );
+					schema.setAttributeProperties( 'baz', { copyOnEnter: true } );
+
+					const allAttributes = ( new Map( [
+						[ 'foo', true ],
+						[ 'bar', true ],
+						[ 'baz', true ]
+					] ) )[ Symbol.iterator ]();
+
+					expect( Array.from( getCopyOnEnterAttributes( schema, allAttributes ) ) ).to.deep.equal(
+						[
+							[ 'foo', true ],
+							[ 'baz', true ]
+						]
+					);
+				} );
+		} );
+	} );
+} );

From 682944016aa999a6cab1c24377cbefdcdfc94cbf Mon Sep 17 00:00:00 2001
From: Mateusz Samsel <m.samsel@cksource.com>
Date: Fri, 12 Jul 2019 12:01:22 +0200
Subject: [PATCH 06/10] Prevent shiftenter to copy attribtues without
 copyOnEnter flag.

---
 src/shiftentercommand.js   |  2 ++
 tests/shiftentercommand.js | 25 +++++++++++++++++++++++++
 2 files changed, 27 insertions(+)

diff --git a/src/shiftentercommand.js b/src/shiftentercommand.js
index 0dd83c5..aea50fa 100644
--- a/src/shiftentercommand.js
+++ b/src/shiftentercommand.js
@@ -84,6 +84,8 @@ function softBreakAction( model, writer, selection ) {
 	if ( isSelectionEmpty ) {
 		const attributesToCopy = getCopyOnEnterAttributes( model.schema, selection.getAttributes() );
 		insertBreak( writer, range.end );
+		// transforms: [ [ key1, value1 ], ... ] => [ key1, ... ]
+		writer.removeSelectionAttribute( Array.from( selection.getAttributes() ).map( x => x[ 0 ] ) );
 		writer.setSelectionAttribute( attributesToCopy );
 	} else {
 		const leaveUnmerged = !( range.start.isAtStart && range.end.isAtEnd );
diff --git a/tests/shiftentercommand.js b/tests/shiftentercommand.js
index ca12217..08b5be6 100644
--- a/tests/shiftentercommand.js
+++ b/tests/shiftentercommand.js
@@ -101,6 +101,31 @@ describe( 'ShiftEnterCommand', () => {
 				'<p>x</p><p>[]foo</p><p>y</p>',
 				'<p>x</p><p><softBreak></softBreak>[]foo</p><p>y</p>'
 			);
+
+			describe( 'copyOnEnter', () => {
+				beforeEach( () => {
+					schema.extend( '$text', { allowAttributes: [ 'foo', 'bar' ] } );
+					schema.setAttributeProperties( 'foo', { copyOnEnter: true } );
+				} );
+
+				test(
+					'allowed attributes are copied',
+					'<p><$text foo="true">test[]</$text></p>',
+					'<p><$text foo="true">test</$text><softBreak></softBreak><$text foo="true">[]</$text></p>'
+				);
+
+				test(
+					'unknown attributes are not copied',
+					'<p><$text bar="true">test[]</$text></p>',
+					'<p><$text bar="true">test</$text><softBreak></softBreak>[]</p>'
+				);
+
+				test(
+					'only allowed attributes are copied from mix set',
+					'<p><$text bar="true" foo="true">test[]</$text></p>',
+					'<p><$text bar="true" foo="true">test</$text><softBreak></softBreak><$text foo="true">[]</$text></p>'
+				);
+			} );
 		} );
 
 		describe( 'non-collapsed selection', () => {

From 0f39ad7bb63faf49a7cbaec253751815a3ae58a9 Mon Sep 17 00:00:00 2001
From: Mateusz Samsel <m.samsel@cksource.com>
Date: Tue, 16 Jul 2019 11:19:40 +0200
Subject: [PATCH 07/10] Update description. Improve unit test.

---
 src/shiftentercommand.js | 2 +-
 src/utils.js             | 6 +++---
 tests/utils.js           | 6 +++---
 3 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/src/shiftentercommand.js b/src/shiftentercommand.js
index aea50fa..77a3b30 100644
--- a/src/shiftentercommand.js
+++ b/src/shiftentercommand.js
@@ -84,7 +84,7 @@ function softBreakAction( model, writer, selection ) {
 	if ( isSelectionEmpty ) {
 		const attributesToCopy = getCopyOnEnterAttributes( model.schema, selection.getAttributes() );
 		insertBreak( writer, range.end );
-		// transforms: [ [ key1, value1 ], ... ] => [ key1, ... ]
+
 		writer.removeSelectionAttribute( Array.from( selection.getAttributes() ).map( x => x[ 0 ] ) );
 		writer.setSelectionAttribute( attributesToCopy );
 	} else {
diff --git a/src/utils.js b/src/utils.js
index f428c7c..831c79f 100644
--- a/src/utils.js
+++ b/src/utils.js
@@ -8,13 +8,13 @@
  */
 
 /**
- * Returns iterator which has filtered attributes read from {@link module:engine/model/selection~Selection#getAttributes selection}.
+ * Returns attributes that should be preserved on the enter key.
  * Filtering is realized based on `copyOnEnter` attribute property. Read more about attribute properties
  * {@link module:engine/model/schema~Schema#setAttributeProperties here}.
  *
  * @param {module:engine/model/schema~Schema} schema
- * @param {Iterable.<*>} allAttributes iterator with attributes of current selection.
- * @returns {Iterable.<*>} filtered attributes which has `copyOnEnter` property.
+ * @param {Iterable.<*>} allAttributes attributes to filter.
+ * @returns {Iterable.<*>}
  */
 export function* getCopyOnEnterAttributes( schema, allAttributes ) {
 	for ( const attribute of allAttributes ) {
diff --git a/tests/utils.js b/tests/utils.js
index 37cb4cb..e1a5831 100644
--- a/tests/utils.js
+++ b/tests/utils.js
@@ -13,9 +13,9 @@ describe( 'utils', () => {
 				.then( editor => {
 					const schema = editor.model.schema;
 
-					schema.register( 'foo', { inheritAllFrom: '$block' } );
-					schema.register( 'bar', { inheritAllFrom: '$block' } );
-					schema.register( 'baz', { inheritAllFrom: '$block' } );
+					schema.extend( '$text', {
+						allowAttributes: [ 'foo', 'bar', 'baz' ]
+					} );
 
 					schema.setAttributeProperties( 'foo', { copyOnEnter: true } );
 					schema.setAttributeProperties( 'baz', { copyOnEnter: true } );

From 005c1558d5436e0d984de9efb167cf3ea7e71ff0 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Maciej=20Go=C5=82aszewski?= <jodator@jodator.net>
Date: Tue, 16 Jul 2019 11:52:37 +0200
Subject: [PATCH 08/10] Improve doclet for getCopyOnEnterAttributes() function.

---
 src/utils.js | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/utils.js b/src/utils.js
index 831c79f..66a68ac 100644
--- a/src/utils.js
+++ b/src/utils.js
@@ -9,6 +9,7 @@
 
 /**
  * Returns attributes that should be preserved on the enter key.
+ *
  * Filtering is realized based on `copyOnEnter` attribute property. Read more about attribute properties
  * {@link module:engine/model/schema~Schema#setAttributeProperties here}.
  *

From a58c94f90a743e742e0d50e241ef04c930f25ec3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Maciej=20Go=C5=82aszewski?= <jodator@jodator.net>
Date: Tue, 16 Jul 2019 11:56:04 +0200
Subject: [PATCH 09/10] Use selection.getAttributeKeys() for selection
 attributes names retrieval.

---
 src/shiftentercommand.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/shiftentercommand.js b/src/shiftentercommand.js
index 77a3b30..fe79752 100644
--- a/src/shiftentercommand.js
+++ b/src/shiftentercommand.js
@@ -85,7 +85,7 @@ function softBreakAction( model, writer, selection ) {
 		const attributesToCopy = getCopyOnEnterAttributes( model.schema, selection.getAttributes() );
 		insertBreak( writer, range.end );
 
-		writer.removeSelectionAttribute( Array.from( selection.getAttributes() ).map( x => x[ 0 ] ) );
+		writer.removeSelectionAttribute( Array.from( selection.getAttributeKeys() ) );
 		writer.setSelectionAttribute( attributesToCopy );
 	} else {
 		const leaveUnmerged = !( range.start.isAtStart && range.end.isAtEnd );

From 88d750dfefa0261c958d0743602667b9c874afda Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Maciej=20Go=C5=82aszewski?= <jodator@jodator.net>
Date: Tue, 16 Jul 2019 12:03:38 +0200
Subject: [PATCH 10/10] Use Itarable directly when calling
 writer.removeSelectionAttribute().

---
 src/shiftentercommand.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/shiftentercommand.js b/src/shiftentercommand.js
index fe79752..ceb6d22 100644
--- a/src/shiftentercommand.js
+++ b/src/shiftentercommand.js
@@ -85,7 +85,7 @@ function softBreakAction( model, writer, selection ) {
 		const attributesToCopy = getCopyOnEnterAttributes( model.schema, selection.getAttributes() );
 		insertBreak( writer, range.end );
 
-		writer.removeSelectionAttribute( Array.from( selection.getAttributeKeys() ) );
+		writer.removeSelectionAttribute( selection.getAttributeKeys() );
 		writer.setSelectionAttribute( attributesToCopy );
 	} else {
 		const leaveUnmerged = !( range.start.isAtStart && range.end.isAtEnd );