Make iOS attributes not reappear in empty lines (#181)

This PR fixes two pretty obscure iOS issues;
- backspacing a line until it's empty made attributes from previous line
be applied in the empty line. It looked especially dumb with
lists/blockquotes that just got put there together with their zero width
spaces (so custom drawing as well)
- just changing selection to an empty line that follows some non empty
line also used the previous line's attributes. This wasn't as bad
because custom drawing from lists/quotes wasn't there, but the indents
from them still were there.

Author: szydlovsky

ios/EnrichedTextInputView.mm

@@ -14,6 +14,7 @@
 #import "WordsUtils.h"
 #import "LayoutManagerExtension.h"
 #import "ZeroWidthSpaceUtils.h"
+#import "ParagraphAttributesUtils.h"
 
 using namespace facebook::react;
 
@@ -977,6 +978,22 @@ - (void)manageSelectionBasedChanges {
     [mentionStyleClass manageMentionTypingAttributes];
     [mentionStyleClass manageMentionEditing];
   }
+  
+  // typing attributes for empty lines selection reset
+  NSString *currentString = [[textView.textStorage.string copy] stringByReplacingOccurrencesOfString:@"\u200B" withString:@""];
+  if(textView.selectedRange.length == 0 && [_recentlyEmittedString isEqualToString: currentString] ) {
+    // no string change means only a selection changed with no character changes
+    NSRange paragraphRange = [textView.textStorage.string paragraphRangeForRange:textView.selectedRange];
+    if(
+      paragraphRange.length == 0 ||
+      (paragraphRange.length == 1 &&
+      [[NSCharacterSet newlineCharacterSet] characterIsMember:[textView.textStorage.string characterAtIndex:paragraphRange.location]])
+    ) {
+      // user changed selection to an empty line (or empty line with a newline)
+      // typing attributes need to be reset
+      textView.typingAttributes = defaultTypingAttributes;
+    }
+  }
 }
 
 - (void)handleWordModificationBasedChanges:(NSString*)word inRange:(NSRange)range {
@@ -1135,7 +1152,8 @@ - (bool)textView:(UITextView *)textView shouldChangeTextInRange:(NSRange)range r
     [h1Style handleNewlinesInRange:range replacementText:text] ||
     [h2Style handleNewlinesInRange:range replacementText:text] ||
     [h3Style handleNewlinesInRange:range replacementText:text] ||
-    [ZeroWidthSpaceUtils handleBackspaceInRange:range replacementText:text input:self]
+    [ZeroWidthSpaceUtils handleBackspaceInRange:range replacementText:text input:self] ||
+    [ParagraphAttributesUtils handleBackspaceInRange:range replacementText:text input:self]
   ) {
     [self anyTextMayHaveBeenModified];
     return NO;

ios/utils/ParagraphAttributesUtils.h

@@ -0,0 +1,6 @@
+#import <UIKit/UIKit.h>
+#pragma once
+
+@interface ParagraphAttributesUtils : NSObject
++ (BOOL)handleBackspaceInRange:(NSRange)range replacementText:(NSString *)text input:(id)input;
+@end

ios/utils/ParagraphAttributesUtils.mm

@@ -0,0 +1,43 @@
+#import "ParagraphAttributesUtils.h"
+#import "EnrichedTextInputView.h"
+#import "ParagraphsUtils.h"
+#import "TextInsertionUtils.h"
+
+@implementation ParagraphAttributesUtils
+
+// if the user backspaces the last character in a line, the iOS applies typing attributes from the previous line
+// in the case of some paragraph styles it works especially bad when a list point just appears
+// hence the solution - reset typing attributes
++ (BOOL)handleBackspaceInRange:(NSRange)range replacementText:(NSString *)text input:(id)input {
+  EnrichedTextInputView *typedInput = (EnrichedTextInputView *)input;
+  if(typedInput == nullptr) {
+    return NO;
+  }
+  
+  // we make sure it was a backspace (text with 0 length) and it deleted something (range longer than 0)
+  if(text.length > 0 || range.length == 0) {
+    return NO;
+  }
+  
+  // find a non-newline range of the paragraph
+  NSRange paragraphRange = [typedInput->textView.textStorage.string paragraphRangeForRange:range];
+  NSArray *paragraphs = [ParagraphsUtils getNonNewlineRangesIn:typedInput->textView range:paragraphRange];
+  if(paragraphs.count == 0) {
+    return NO;
+  }
+  
+  NSRange nonNewlineRange = [(NSValue *)paragraphs.firstObject rangeValue];
+  
+  // if the backspace removes the whole content of a paragraph - do the thing
+  if(NSEqualRanges(nonNewlineRange, range)) {
+    // do the replacement manually
+    [TextInsertionUtils replaceText:text at:range additionalAttributes:nullptr input:typedInput withSelection:YES];
+    // reset typing attribtues
+    typedInput->textView.typingAttributes = typedInput->defaultTypingAttributes;
+    return YES;
+  }
+
+  return NO;
+}
+
+@end