introduce pluralizer: partially restore the original "forced" semantics

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

@@ -63,7 +63,7 @@ class Pluralizer {
    * Pass in a word token to produce a function that can replicate the case on
    * another word.
    */
-  private static String restoreCase(String word, String result) {
+  static String restoreCase(String word, String result) {
     if (word == null || result == null || word == result) return result;
     char[] chars = result.toCharArray();
     boolean prevUp = false;
@@ -173,20 +173,20 @@ class Pluralizer {
      */
     JBIterable.of(new String[][]{
       // Pronouns.
-      {"I", "we"},
-      {"me", "us"},
-      {"he", "they"},
-      {"she", "they"},
-      {"them", "them"},
-      {"myself", "ourselves"},
-      {"yourself", "yourselves"},
-      {"itself", "themselves"},
-      {"herself", "themselves"},
-      {"himself", "themselves"},
-      {"themself", "themselves"},
-      {"is", "are"},
-      {"was", "were"},
-      {"has", "have"},
+      //{"I", "we"},
+      //{"me", "us"},
+      //{"he", "they"},
+      //{"she", "they"},
+      //{"them", "them"},
+      //{"myself", "ourselves"},
+      //{"yourself", "yourselves"},
+      //{"itself", "themselves"},
+      //{"herself", "themselves"},
+      //{"himself", "themselves"},
+      //{"themself", "themselves"},
+      //{"is", "are"},
+      //{"was", "were"},
+      //{"has", "have"},
       {"this", "these"},
       {"that", "those"},
       // Words ending in with a consonant and `o`.

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

@@ -832,7 +832,9 @@ public class StringUtil extends StringUtilRt {
   @NotNull
   @Contract(pure = true)
   public static String pluralize(@NotNull String word) {
-    return Pluralizer.PLURALIZER.plural(word);
+    String plural = Pluralizer.PLURALIZER.plural(word);
+    return equalsIgnoreCase(plural, word) && !endsWithIgnoreCase(plural, "es") ?
+           Pluralizer.restoreCase(word, word + "s") : plural;
   }
 
   @NotNull
@@ -1645,13 +1647,17 @@ public class StringUtil extends StringUtilRt {
    * Returns unpluralized variant using English based heuristics like properties -> property, names -> name, children -> child.
    * Returns <code>null</code> if failed to match appropriate heuristic.
    *
-   * @param name english word in plural form
+   * @param word english word in plural form
    * @return name in singular form or <code>null</code> if failed to find one.
    */
   @Nullable
   @Contract(pure = true)
   public static String unpluralize(@NotNull String word) {
-    return Pluralizer.PLURALIZER.singular(word);
+    String singular = Pluralizer.PLURALIZER.singular(word);
+    if (equalsIgnoreCase(singular, word)) {
+      singular = nullize(trimEnd(singular, "s", true));
+    }
+    return equalsIgnoreCase(singular, word) ? null : singular;
   }
 
   @Contract(pure = true)

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

@@ -98,7 +98,9 @@ public class StringUtilTest {
 
   @Test
   public void testUnPluralize() {
-    assertEquals("s", StringUtil.unpluralize("s"));
+    assertEquals("plurals", StringUtil.unpluralize("pluralss"));
+    assertEquals("I", StringUtil.unpluralize("Is"));
+    assertEquals(null, StringUtil.unpluralize("s"));
     assertEquals("z", StringUtil.unpluralize("zs"));
     assertEquals("Index", StringUtil.unpluralize("Indices"));
     assertEquals("fix", StringUtil.unpluralize("fixes"));