Check for index bounds in RTL handling for trailing whitespace runs. (#12336)

* Check for special case index out of bounds condition for leading space

* Add TODO

* Rework to pass tests

* More robust check for leading

* Minor adjustment

* Fix order bug

* Do not modify for leading space

* Fix test value

* Condition

Author: GaryQian

third_party/txt/src/txt/paragraph_txt.cc

@@ -415,6 +415,9 @@ bool ParagraphTxt::ComputeBidiRuns(std::vector<BidiRun>* result) {
   //
   // This only applies to the final whitespace at the end as other whitespace is
   // no longer ambiguous when surrounded by additional text.
+
+  // TODO(garyq): Handle this in the text editor caret code instead at layout
+  // level.
   bool has_trailing_whitespace = false;
   int32_t bidi_run_start, bidi_run_length;
   if (bidi_run_count > 1) {
@@ -427,8 +430,17 @@ bool ParagraphTxt::ComputeBidiRuns(std::vector<BidiRun>* result) {
       U16_GET(text_.data(), 0, bidi_run_start + bidi_run_length - 1,
               static_cast<int>(text_.size()), last_char);
       if (u_hasBinaryProperty(last_char, UCHAR_WHITE_SPACE)) {
-        has_trailing_whitespace = true;
-        bidi_run_count--;
+        // Check if the trailing whitespace occurs before the previous run or
+        // not. If so, this trailing whitespace was a leading whitespace.
+        int32_t second_last_bidi_run_start, second_last_bidi_run_length;
+        ubidi_getVisualRun(bidi.get(), bidi_run_count - 2,
+                           &second_last_bidi_run_start,
+                           &second_last_bidi_run_length);
+        if (bidi_run_start ==
+            second_last_bidi_run_start + second_last_bidi_run_length) {
+          has_trailing_whitespace = true;
+          bidi_run_count--;
+        }
       }
     }
   }

third_party/txt/tests/paragraph_unittests.cc

@@ -2327,6 +2327,57 @@ TEST_F(ParagraphTest, DISABLE_ON_WINDOWS(JustifyRTLNewLine)) {
   }
 }
 
+TEST_F(ParagraphTest, DISABLE_ON_WINDOWS(LeadingSpaceRTL)) {
+  const char* text = " leading space";
+
+  auto icu_text = icu::UnicodeString::fromUTF8(text);
+  std::u16string u16_text(icu_text.getBuffer(),
+                          icu_text.getBuffer() + icu_text.length());
+
+  txt::ParagraphStyle paragraph_style;
+  paragraph_style.max_lines = 14;
+  paragraph_style.text_align = TextAlign::justify;
+  paragraph_style.text_direction = TextDirection::rtl;
+  txt::ParagraphBuilderTxt builder(paragraph_style, GetTestFontCollection());
+
+  txt::TextStyle text_style;
+  text_style.font_families = std::vector<std::string>(1, "Ahem");
+  text_style.font_size = 26;
+  text_style.color = SK_ColorBLACK;
+  text_style.height = 1;
+  builder.PushStyle(text_style);
+
+  builder.AddText(u16_text);
+
+  builder.Pop();
+
+  auto paragraph = BuildParagraph(builder);
+  size_t paragraph_width = GetTestCanvasWidth() - 100;
+  paragraph->Layout(paragraph_width);
+
+  paragraph->Paint(GetCanvas(), 0, 0);
+
+  SkPaint paint;
+  paint.setStyle(SkPaint::kStroke_Style);
+  paint.setAntiAlias(true);
+  paint.setStrokeWidth(1);
+
+  // Tests for GetRectsForRange()
+  Paragraph::RectHeightStyle rect_height_style =
+      Paragraph::RectHeightStyle::kMax;
+  Paragraph::RectWidthStyle rect_width_style =
+      Paragraph::RectWidthStyle::kTight;
+  paint.setColor(SK_ColorRED);
+  std::vector<txt::Paragraph::TextBox> boxes =
+      paragraph->GetRectsForRange(0, 100, rect_height_style, rect_width_style);
+  for (size_t i = 0; i < boxes.size(); ++i) {
+    GetCanvas()->drawRect(boxes[i].rect, paint);
+  }
+  ASSERT_EQ(boxes.size(), 2ull);
+
+  // This test should crash if behavior regresses.
+}
+
 TEST_F(ParagraphTest, DecorationsParagraph) {
   txt::ParagraphStyle paragraph_style;
   paragraph_style.max_lines = 14;