Further optimization to TextFormatEscaper

In the case of quotes and backslashes (which are the most common things that need escaping) we can avoid going into Utf8 bytes for most cases this way, while also only doing 1 pass over the string when it doesn't need escaping at all.

PiperOrigin-RevId: 862311595

Author: protobuf-github-bot

java/core/src/main/java/com/google/protobuf/TextFormatEscaper.java

@@ -88,19 +88,51 @@ static String escapeBytes(final ByteString input) {
     return escapeBytes(input.toByteArray());
   }
 
-  static boolean needsEscape(char c) {
-    return c < 0x20 || c > 0x7e || c == '\'' || c == '"' || c == '\\';
-  }
-
   /** Like {@link #escapeBytes(ByteString)}, but escapes a text string. */
   static String escapeText(String input) {
-    // Loop on the string to see if any character even needs escaping. If yes, then convert into
-    // UTF-8 and then escape on those bytes. If not, we can just return the original input.
+    boolean hasSingleQuote = false;
+    boolean hasDoubleQuote = false;
+    boolean hasBackslash = false;
+
     for (int i = 0; i < input.length(); ++i) {
-      if (needsEscape(input.charAt(i))) {
+      char c = input.charAt(i);
+
+      // If there are any characters outside of ASCII range we eagerly convert to UTF and escape on
+      // those bytes. Note that escaping to UTF8 bytes instead of \\u sequences is itself somewhat
+      // nonsensical, but JavaProto has behaved this way for a long time, and changing the behavior
+      // would be disruptive.
+      if (c < 0x20 || c > 0x7e) {
         return escapeBytes(input.getBytes(Internal.UTF_8));
       }
+
+      // While in this loop, keep track if there are any single quotes, double quotes, or
+      // backslashes. This can help avoid multiple passes over the string looking for each of the
+      // bad characters.
+      switch (c) {
+        case '\'':
+          hasSingleQuote = true;
+          break;
+        case '"':
+          hasDoubleQuote = true;
+          break;
+        case '\\':
+          hasBackslash = true;
+          break;
+        default:
+          break;
+      }
     }
+
+    if (hasSingleQuote) {
+      input = input.replace("\'", "\\\'");
+    }
+    if (hasDoubleQuote) {
+      input = input.replace("\"", "\\\"");
+    }
+    if (hasBackslash) {
+      input = input.replace("\\", "\\\\");
+    }
+
     return input;
   }