From 13a959ce67c2aa4234002af34dae83a911829ecc Mon Sep 17 00:00:00 2001
From: Alexey Andreev <konsoletyper@gmail.com>
Date: Thu, 18 Jul 2024 18:51:42 +0200
Subject: [PATCH] classlib: fix String.replace, add optimizations for some
 corner cases

Fix #932
---
 .../org/teavm/classlib/java/lang/TString.java | 41 +++++++++++++------
 .../teavm/classlib/java/lang/StringTest.java  |  3 ++
 2 files changed, 31 insertions(+), 13 deletions(-)

diff --git a/classlib/src/main/java/org/teavm/classlib/java/lang/TString.java b/classlib/src/main/java/org/teavm/classlib/java/lang/TString.java
index 6488165fb..fa0ca07ff 100644
--- a/classlib/src/main/java/org/teavm/classlib/java/lang/TString.java
+++ b/classlib/src/main/java/org/teavm/classlib/java/lang/TString.java
@@ -501,22 +501,37 @@ public class TString extends TObject implements TSerializable, TComparable<TStri
     }
 
     public String replace(TCharSequence target, TCharSequence replacement) {
-        var sb = new StringBuilder();
-        int sz = length() - target.length();
-        int i = 0;
-        outer:
-        for (; i <= sz; ++i) {
-            for (int j = 0; j < target.length(); ++j) {
-                if (charAt(i + j) != target.charAt(j)) {
-                    sb.append(charAt(i));
-                    continue outer;
-                }
+        if (target == replacement) {
+            return (String) (Object) this;
+        } else if (target.isEmpty()) {
+            var sb = new StringBuilder();
+            for (var i = 0; i < length(); ++i) {
+                sb.append(replacement);
+                sb.append(charAt(i));
             }
             sb.append(replacement);
-            i += target.length() - 1;
+            return sb.toString();
+        } else if (target.length() == 1 && replacement.length() == 1) {
+            return (String) (Object) replace(target.charAt(0), replacement.charAt(0));
+        } else {
+            var sb = new StringBuilder();
+            int sz = length() - target.length();
+            int i = 0;
+            outer:
+            for (; i <= sz; ++i) {
+                for (int j = 0; j < target.length(); ++j) {
+                    if (charAt(i + j) != target.charAt(j)) {
+                        sb.append(charAt(i));
+                        continue outer;
+                    }
+                }
+                sb.append(replacement);
+                i += target.length() - 1;
+            }
+            sb.append(substring(i));
+
+            return sb.toString();
         }
-        sb.append(substring(i));
-        return sb.toString();
     }
 
     public TString trim() {
diff --git a/tests/src/test/java/org/teavm/classlib/java/lang/StringTest.java b/tests/src/test/java/org/teavm/classlib/java/lang/StringTest.java
index e62ae11ef..045821b7d 100644
--- a/tests/src/test/java/org/teavm/classlib/java/lang/StringTest.java
+++ b/tests/src/test/java/org/teavm/classlib/java/lang/StringTest.java
@@ -197,6 +197,9 @@ public class StringTest {
     @Test
     public void sequenceReplaced() {
         assertEquals("ba", "aaa".replace("aa", "b"));
+        assertEquals("xaxaxax", "aaa".replace("", "x"));
+        assertEquals("axc", "abc".replace("b", "x"));
+        assertEquals("abc", "abc".replace("bc", "bc"));
     }
 
     @Test