avoid converting CharSequence to String to save memory

platform/util/src/com/intellij/openapi/util/text/StringUtil.java

@@ -2024,13 +2024,25 @@ public class StringUtil extends StringUtilRt {
   @NotNull
   @Contract(pure = true)
   public static CharSequence first(@NotNull CharSequence text, final int length, final boolean appendEllipsis) {
-    return text.length() > length ? text.subSequence(0, length) + (appendEllipsis ? "..." : "") : text;
+    if (text.length() <= length) {
+      return text;
+    }
+    if (appendEllipsis) {
+      return text.subSequence(0, length) + "...";
+    }
+    return text.subSequence(0, length);
   }
 
   @NotNull
   @Contract(pure = true)
   public static CharSequence last(@NotNull CharSequence text, final int length, boolean prependEllipsis) {
-    return text.length() > length ? (prependEllipsis ? "..." : "") + text.subSequence(text.length() - length, text.length()) : text;
+    if (text.length() <= length) {
+      return text;
+    }
+    if (prependEllipsis) {
+      return "..." + text.subSequence(text.length() - length, text.length());
+    }
+    return text.subSequence(text.length() - length, text.length());
   }
 
   @NotNull

platform/util/testSrc/com/intellij/util/text/StringUtilTest.java

@@ -743,4 +743,16 @@ public class StringUtilTest {
     assertEquals(LineColumn.of(2, 1), StringUtil.offsetToLineColumn("abc\n\nabc", 6));
     assertEquals(LineColumn.of(1, 1), StringUtil.offsetToLineColumn("abc\r\nabc", 6));
   }
+
+  @Test
+  public void testFirstLastDontConvertCharSequenceToString() {
+    CharSequence s = ByteArrayCharSequence.convertToBytesIfAsciiString("test");
+    assertTrue(s instanceof ByteArrayCharSequence);
+    CharSequence first = StringUtil.first(s, 1, false);
+    assertTrue(String.valueOf(first.getClass()), first instanceof CharSequenceSubSequence);
+    assertEquals("t", first.toString());
+    CharSequence last = StringUtil.last(s, 1, false);
+    assertTrue(String.valueOf(last.getClass()), last instanceof CharSequenceSubSequence);
+    assertEquals("t", last.toString());
+  }
 }