Stop trying to autosave when title and classic block content both are…

… empty. (#10404)

* Do not auto-update if title and classic block content is empty.

* Update isEditedPostEmpty: use hasKnownBlocks and check if freeform or unregistered or empty content block is available in post.

* Update isEditablePost logic to check length of availalbe block first.

* Editor: Improve selector consideration of empty content edit

packages/editor/src/store/selectors.js

@@ -372,14 +372,32 @@ export function isEditedPostSaveable( state ) {
  * @return {boolean} Whether post has content.
  */
 export function isEditedPostEmpty( state ) {
-	// While the condition of truthy content string would be sufficient for
-	// determining emptiness, testing saveable blocks length is a trivial
-	// operation by comparison. Since this function can be called frequently,
-	// optimize for the fast case where saveable blocks are non-empty.
-	return (
-		! getBlocksForSerialization( state ).length &&
-		! getEditedPostAttribute( state, 'content' )
-	);
+	const blocks = getBlocksForSerialization( state );
+
+	// While the condition of truthy content string is sufficient to determine
+	// emptiness, testing saveable blocks length is a trivial operation. Since
+	// this function can be called frequently, optimize for the fast case as a
+	// condition of the mere existence of blocks. Note that the value of edited
+	// content is used in place of blocks, thus allowed to fall through.
+	if ( blocks.length && ! ( 'content' in getPostEdits( state ) ) ) {
+		// Pierce the abstraction of the serializer in knowing that blocks are
+		// joined with with newlines such that even if every individual block
+		// produces an empty save result, the serialized content is non-empty.
+		if ( blocks.length > 1 ) {
+			return false;
+		}
+
+		// Freeform and unregistered blocks omit comment delimiters in their
+		// output. The freeform block specifically may produce an empty string
+		// to save. In the case of a single freeform block, fall through to the
+		// full serialize. Otherwise, the single block is assumed non-empty by
+		// virtue of its comment delimiters.
+		if ( blocks[ 0 ].name !== getFreeformContentHandlerName() ) {
+			return false;
+		}
+	}
+
+	return ! getEditedPostContent( state );
 }
 
 /**