From b38593d714c4b65c3e0c767ecaeea3496d6d24b9 Mon Sep 17 00:00:00 2001
From: Colin Alworth <colin@vertispan.com>
Date: Sun, 8 Dec 2024 20:03:40 -0600
Subject: [PATCH] Fix a bug, and fix unit tests for constant folding

---
 .../com/google/gwt/emul/java/lang/String.java |  2 +-
 .../java/lang/CompilerConstantStringTest.java | 27 ++++++++++++++-----
 .../gwt/emultest/java/lang/StringTest.java    | 14 ++++++++--
 3 files changed, 34 insertions(+), 9 deletions(-)

diff --git a/user/super/com/google/gwt/emul/java/lang/String.java b/user/super/com/google/gwt/emul/java/lang/String.java
index ed2179f08c8..42af2f1fe5e 100644
--- a/user/super/com/google/gwt/emul/java/lang/String.java
+++ b/user/super/com/google/gwt/emul/java/lang/String.java
@@ -654,7 +654,7 @@ public String[] split(String regex, int maxMatch) {
       } else {
         int matchIndex = matchObj.getIndex();
 
-        if (lastTrail == null && matchIndex == 0) {
+        if (lastTrail == null && matchIndex == 0 && matchObj.asArray()[0].length() == 0) {
           // As of Java 8, we should discard the first zero-length match if it is the beginning of
           // the string. Do not increment the count, and do not add to the output array.
           trail = trail.substring(matchIndex + matchObj.asArray()[0].length(), trail.length());
diff --git a/user/test/com/google/gwt/emultest/java/lang/CompilerConstantStringTest.java b/user/test/com/google/gwt/emultest/java/lang/CompilerConstantStringTest.java
index fc58bdcbded..82aa4a8f02b 100644
--- a/user/test/com/google/gwt/emultest/java/lang/CompilerConstantStringTest.java
+++ b/user/test/com/google/gwt/emultest/java/lang/CompilerConstantStringTest.java
@@ -245,15 +245,30 @@ public void testSplit() {
         "b", "", ":and:f"});
     compareList("0:", "boo:and:foo".split(":", 0), new String[] {
         "boo", "and", "foo"});
-  }
+    // issue 2742
+    compareList("issue2742", new String[] {}, "/".split("/", 0));
+
+    // Splitting an empty string should result in an array containing a single
+    // empty string.
+    String[] s = "".split(",");
+    assertTrue(s != null);
+    assertTrue(s.length == 1);
+    assertTrue(s[0] != null);
+    assertTrue(s[0].length() == 0);
+
+    s = "abcada".split("a");
+    assertTrue(s != null);
+    assertEquals(3, s.length);
+    assertEquals("", s[0]);
+    assertEquals("bc", s[1]);
+    assertEquals("d", s[2]);  }
 
   public void testSplit_emptyExpr() {
-    // TODO(rluble):  implement JDK8 string.split semantics and fix test.
-    // See issue 8913.
-    String[] expected = (TestUtils.getJdkVersion() > 7) ?
-        new String[] {"a", "b", "c", "x", "x", "d", "e", "x", "f", "x"} :
-        new String[] {"", "a", "b", "c", "x", "x", "d", "e", "x", "f", "x"};
+    String[] expected = new String[] {"a", "b", "c", "x", "x", "d", "e", "x", "f", "x"};
     compareList("emptyRegexSplit", expected, "abcxxdexfx".split(""));
+
+    String[] arr = ",".split(",");
+    assertEquals(0, arr.length);
   }
 
   public void testStartsWith() {
diff --git a/user/test/com/google/gwt/emultest/java/lang/StringTest.java b/user/test/com/google/gwt/emultest/java/lang/StringTest.java
index 75c4053fe6f..c1c436e4b3a 100644
--- a/user/test/com/google/gwt/emultest/java/lang/StringTest.java
+++ b/user/test/com/google/gwt/emultest/java/lang/StringTest.java
@@ -781,20 +781,30 @@ public void testSplit() {
 
     // Splitting an empty string should result in an array containing a single
     // empty string.
-    String[] s = "".split(",");
+    String[] s = hideFromCompiler("").split(",");
     assertTrue(s != null);
     assertTrue(s.length == 1);
     assertTrue(s[0] != null);
     assertTrue(s[0].length() == 0);
+
+    s = hideFromCompiler("abcada").split("a");
+    assertTrue(s != null);
+    assertEquals(3, s.length);
+    assertEquals("", s[0]);
+    assertEquals("bc", s[1]);
+    assertEquals("d", s[2]);
   }
 
   public void testSplit_emptyExpr() {
     String[] expected = new String[] {"a", "b", "c", "x", "x", "d", "e", "x", "f", "x"};
     compareList("emptyRegexSplit", expected, hideFromCompiler("abcxxdexfx").split(""));
+
+    String[] arr = hideFromCompiler(",").split(",");
+    assertEquals(0, arr.length);
   }
 
   public void testStartsWith() {
-    String haystack = "abcdefghi";
+    String haystack = hideFromCompiler("abcdefghi");
     assertTrue(haystack.startsWith("abc"));
     assertTrue(haystack.startsWith("bc", 1));
     assertTrue(haystack.startsWith(haystack));