Resolve WebCore::findWordBoundary crash

rdar://128246589
https://bugs.webkit.org/show_bug.cgi?id=273907

Reviewed by Wenson Hsieh.

Fix empty string case to resolve findWordBoundary crash

Combined changes:
* Source/WebCore/platform/text/mac/TextBoundaries.mm:
(WebCore::findWordBoundary):

Canonical link: https://commits.webkit.org/279076@main

Source/WebCore/platform/text/mac/TextBoundaries.mm

@@ -186,9 +186,15 @@ void findWordBoundary(StringView text, int position, int* start, int* end)
     *start = range.location;
     *end = range.location + range.length;
 #else
+    if (text.isEmpty()) {
+        *start = 0;
+        *end = 0;
+        return;
+    }
+
     unsigned pos = position;
-    if (pos == text.length() && pos)
-        --pos;
+    if (pos >= text.length() && pos)
+        pos = text.length() - 1;
 
     // For complex text (Thai, Japanese, Chinese), visible_units will pass the text in as a 
     // single contiguous run of characters, providing as much context as is possible.

Tools/TestWebKitAPI/TestWebKitAPI.xcodeproj/project.pbxproj

@@ -97,6 +97,7 @@
 		11C2598D21FA6324004C9E23 /* async-script-load.html in Copy Resources */ = {isa = PBXBuildFile; fileRef = 11C2598C21FA618D004C9E23 /* async-script-load.html */; };
 		143DDE9820C9018B007F76FA /* Security.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = 574F55D0204D471C002948C6 /* Security.framework */; };
 		14CC42E624B8D8FA00E64F48 /* JSRunLoopTimer.mm in Sources */ = {isa = PBXBuildFile; fileRef = 14CC42E524B8D8FA00E64F48 /* JSRunLoopTimer.mm */; };
+		155B87332BF55D7800D93968 /* TextBoundaries.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 155B872B2BF55D7800D93968 /* TextBoundaries.cpp */; };
 		1A02C870125D4CFD00E3F4BD /* find.html in Copy Resources */ = {isa = PBXBuildFile; fileRef = 1A02C84B125D4A5E00E3F4BD /* find.html */; };
 		1A3524AE1D63A4FB0031729B /* Scope.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 1A3524AC1D63A4FB0031729B /* Scope.cpp */; };
 		1A4F81CF1BDFFD53004E672E /* RemoteObjectRegistryPlugIn.mm in Sources */ = {isa = PBXBuildFile; fileRef = 1A4F81CD1BDFFD53004E672E /* RemoteObjectRegistryPlugIn.mm */; };
@@ -2110,6 +2111,7 @@
 		144D40EC221B46A7004B474F /* UUID.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = UUID.cpp; sourceTree = "<group>"; };
 		14CC42E524B8D8FA00E64F48 /* JSRunLoopTimer.mm */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.objcpp; path = JSRunLoopTimer.mm; sourceTree = "<group>"; };
 		14F3B11215E45EAB00210069 /* SaturatedArithmeticOperations.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = SaturatedArithmeticOperations.cpp; sourceTree = "<group>"; };
+		155B872B2BF55D7800D93968 /* TextBoundaries.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = TextBoundaries.cpp; sourceTree = "<group>"; };
 		1A02C84B125D4A5E00E3F4BD /* find.html */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = text.html; path = find.html; sourceTree = "<group>"; };
 		1A02C84E125D4A8400E3F4BD /* Find.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = Find.cpp; sourceTree = "<group>"; };
 		1A3524A91D627BD40031729B /* DeletedAddressOfOperator.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = DeletedAddressOfOperator.h; sourceTree = "<group>"; };
@@ -4524,6 +4526,7 @@
 				CE4D5DE51F6743BA0072CFC6 /* StringWithDirection.cpp */,
 				41E67A8425D16E83007B0A4C /* STUNMessageParsingTest.cpp */,
 				1C9DD9222697655B00274DB2 /* SVGImageCasts.cpp */,
+				155B872B2BF55D7800D93968 /* TextBoundaries.cpp */,
 				93A258981F92FF15003E510C /* TextCodec.cpp */,
 				CDC2C7141797089D00E627FB /* TimeRanges.cpp */,
 				7AD3FE8D1D75FB8D00B169A4 /* TransformationMatrix.cpp */,
@@ -6857,6 +6860,7 @@
 				F4517B672054C49500C26721 /* TestWKWebViewController.mm in Sources */,
 				F472E00327D966F200F3A172 /* TextAlternatives.mm in Sources */,
 				F45033F5206BEC95009351CE /* TextAutosizingBoost.mm in Sources */,
+				155B87332BF55D7800D93968 /* TextBoundaries.cpp in Sources */,
 				93E6193B1F931B3A00AF245E /* TextCodec.cpp in Sources */,
 				CE3524F91B1441C40028A7C5 /* TextFieldDidBeginAndEndEditing.cpp in Sources */,
 				F494B36A263120780060A310 /* TextServicesTests.mm in Sources */,

Tools/TestWebKitAPI/Tests/WebCore/TextBoundaries.cpp

@@ -0,0 +1,43 @@
+/*
+ * Copyright (C) 2024 Apple Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
+ * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
+ * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
+ * THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "config.h"
+#include <WebCore/TextBoundaries.h>
+
+namespace TestWebKitAPI {
+
+TEST(TextBoundariesTest, FindWordBoundaryEmpty)
+{
+    WTF::String emptyString(""_s);
+    WTF::StringView stringView(emptyString);
+    int start = -1;
+    int end = -1;
+
+    WebCore::findWordBoundary(stringView, 0, &start, &end);
+
+    ASSERT(!start);
+    ASSERT(!end);
+}
+}