Compact layout / widow reduction.

Signal/src/ViewControllers/ConversationView/Cells/OWSMessageBubbleView.m

@@ -855,6 +855,38 @@ NS_ASSUME_NONNULL_BEGIN
 
     OWSMessageTextView *bodyTextView = [self configureBodyTextView];
     CGSize textSize = CGSizeCeil([bodyTextView sizeThatFits:CGSizeMake(maxTextWidth, CGFLOAT_MAX)]);
+
+    // "Compact" layout to reduce "widows",
+    // e.g. last lines with only a single word.
+    //
+    // After measuring the size of the text, we try to find smaller widths
+    // in which the text will fit without adding any height, by wrapping
+    // more text onto the last line. We use a binary search.
+    if (textSize.width > 0 && textSize.height > 0) {
+        NSUInteger upperBound = (NSUInteger)textSize.width;
+        NSUInteger lowerBound = 1;
+        // The more iterations we perform in our binary search,
+        // the more accurate the result, but the more expensive
+        // layout becomes.
+        const int kMaxIterations = 5;
+        for (int i = 0; i < kMaxIterations; i++) {
+            NSUInteger resizeWidth = (upperBound + lowerBound) / 2;
+            if (resizeWidth >= upperBound || resizeWidth <= lowerBound) {
+                break;
+            }
+            CGSize resizeSize = CGSizeCeil([bodyTextView sizeThatFits:CGSizeMake(resizeWidth, CGFLOAT_MAX)]);
+            BOOL success
+                = (resizeSize.width > 0 && resizeSize.width <= resizeWidth && resizeSize.height <= textSize.height);
+            if (success) {
+                // Success.
+                textSize = resizeSize;
+                upperBound = (NSUInteger)textSize.width;
+            } else {
+                // Failure.
+                lowerBound = resizeWidth;
+            }
+        }
+    }
     textSize.width = MIN(textSize.width, maxTextWidth);
     CGSize result = textSize;