[DatePicker] Fix date input hints

lib/java/com/google/android/material/datepicker/UtcDates.java

@@ -167,17 +167,75 @@ static SimpleDateFormat getDefaultTextInputFormat() {
   }
 
   static String getDefaultTextInputHint(Resources res, SimpleDateFormat format) {
-    String formatHint = format.toPattern();
-    String yearChar = res.getString(R.string.mtrl_picker_text_input_year_abbr);
-    String monthChar = res.getString(R.string.mtrl_picker_text_input_month_abbr);
-    String dayChar = res.getString(R.string.mtrl_picker_text_input_day_abbr);
-
-    // Remove duplicate characters for Korean.
-    if (Locale.getDefault().getLanguage().equals(Locale.KOREAN.getLanguage())) {
-      formatHint = formatHint.replaceAll("d+", "d").replaceAll("M+", "M").replaceAll("y+", "y");
+    String datePattern = format.toPattern();
+
+    final String yearAbbr = res.getString(R.string.mtrl_picker_text_input_year_abbr);
+    final String monthAbbr = res.getString(R.string.mtrl_picker_text_input_month_abbr);
+    final String dayAbbr = res.getString(R.string.mtrl_picker_text_input_day_abbr);
+
+    final boolean abbrsArePlaceholders =
+        res.getBoolean(R.bool.mtrl_picker_text_input_hint_abbrs_are_placeholders);
+
+    return abbrsArePlaceholders
+        ? replaceOneLetterFormatSpecifiers(datePattern, yearAbbr, monthAbbr, dayAbbr)
+        : replaceFormatSpecifiers(datePattern, yearAbbr, monthAbbr, dayAbbr);
+  }
+
+  private static String replaceOneLetterFormatSpecifiers(
+      String datePattern, String yearAbbr, String monthAbbr, String dayAbbr) {
+    final StringBuilder stringBuilder = new StringBuilder();
+    for (int i = 0; i < datePattern.length(); i++) {
+      char ch = datePattern.charAt(i);
+      switch (ch) {
+        case 'y':
+          stringBuilder.append(yearAbbr);
+          break;
+        case 'M':
+          stringBuilder.append(monthAbbr);
+          break;
+        case 'd':
+          stringBuilder.append(dayAbbr);
+          break;
+        default:
+          stringBuilder.append(ch);
+          break;
+      }
+    }
+
+    return stringBuilder.toString();
+  }
+
+  private static String replaceFormatSpecifiers(
+      String datePattern, String yearAbbr, String monthAbbr, String dayAbbr) {
+    final StringBuilder stringBuilder = new StringBuilder();
+
+    char prevCh = 0;
+    for (int i = 0; i < datePattern.length(); i++) {
+      char ch = datePattern.charAt(i);
+      switch (ch) {
+        case 'y':
+          if (prevCh != 'y') {
+            stringBuilder.append(yearAbbr);
+          }
+          break;
+        case 'M':
+          if (prevCh != 'M') {
+            stringBuilder.append(monthAbbr);
+          }
+          break;
+        case 'd':
+          if (prevCh != 'd') {
+            stringBuilder.append(dayAbbr);
+          }
+          break;
+        default:
+          stringBuilder.append(ch);
+          break;
+      }
+      prevCh = ch;
     }
 
-    return formatHint.replace("d", dayChar).replace("M", monthChar).replace("y", yearChar);
+    return stringBuilder.toString();
   }
 
   /**

lib/java/com/google/android/material/datepicker/res/values-az/bools.xml

@@ -0,0 +1,20 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!--
+    Copyright 2024 The Android Open Source Project
+
+    Licensed under the Apache License, Version 2.0 (the "License");
+    you may not use this file except in compliance with the License.
+    You may obtain a copy of the License at
+
+        http://www.apache.org/licenses/LICENSE-2.0
+
+    Unless required by applicable law or agreed to in writing, software
+    distributed under the License is distributed on an "AS IS" BASIS,
+    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+    See the License for the specific language governing permissions and
+    limitations under the License.
+-->
+
+<resources>
+  <bool name="mtrl_picker_text_input_hint_abbrs_are_placeholders">false</bool>
+</resources>

lib/java/com/google/android/material/datepicker/res/values-ko/bools.xml

@@ -0,0 +1,20 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!--
+    Copyright 2024 The Android Open Source Project
+
+    Licensed under the Apache License, Version 2.0 (the "License");
+    you may not use this file except in compliance with the License.
+    You may obtain a copy of the License at
+
+        http://www.apache.org/licenses/LICENSE-2.0
+
+    Unless required by applicable law or agreed to in writing, software
+    distributed under the License is distributed on an "AS IS" BASIS,
+    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+    See the License for the specific language governing permissions and
+    limitations under the License.
+-->
+
+<resources>
+  <bool name="mtrl_picker_text_input_hint_abbrs_are_placeholders">false</bool>
+</resources>

lib/java/com/google/android/material/datepicker/res/values-zh-rHK/bools.xml

@@ -0,0 +1,20 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!--
+    Copyright 2024 The Android Open Source Project
+
+    Licensed under the Apache License, Version 2.0 (the "License");
+    you may not use this file except in compliance with the License.
+    You may obtain a copy of the License at
+
+        http://www.apache.org/licenses/LICENSE-2.0
+
+    Unless required by applicable law or agreed to in writing, software
+    distributed under the License is distributed on an "AS IS" BASIS,
+    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+    See the License for the specific language governing permissions and
+    limitations under the License.
+-->
+
+<resources>
+  <bool name="mtrl_picker_text_input_hint_abbrs_are_placeholders">false</bool>
+</resources>

lib/java/com/google/android/material/datepicker/res/values/bools.xml

@@ -0,0 +1,20 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!--
+    Copyright 2024 The Android Open Source Project
+
+    Licensed under the Apache License, Version 2.0 (the "License");
+    you may not use this file except in compliance with the License.
+    You may obtain a copy of the License at
+
+        http://www.apache.org/licenses/LICENSE-2.0
+
+    Unless required by applicable law or agreed to in writing, software
+    distributed under the License is distributed on an "AS IS" BASIS,
+    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+    See the License for the specific language governing permissions and
+    limitations under the License.
+-->
+
+<resources>
+  <bool name="mtrl_picker_text_input_hint_abbrs_are_placeholders">true</bool>
+</resources>

lib/javatests/com/google/android/material/datepicker/UtcDatesTest.java

@@ -78,6 +78,15 @@ public void textInputHintWith1CharYearLocalized() {
     assertEquals("m/j/a", hint);
   }
 
+  @Test
+  @Config(qualifiers = "az")
+  public void textInputHintForAzerbaijani() {
+    SimpleDateFormat sdf = new SimpleDateFormat("dd.MM.yy");
+    String hint = UtcDates.getDefaultTextInputHint(context.getResources(), sdf);
+
+    assertEquals("gün.ay.il", hint);
+  }
+
   @Test
   @Config(qualifiers = "ko")
   public void textInputHintForKorean() {
@@ -87,6 +96,15 @@ public void textInputHintForKorean() {
     assertEquals("년.월.일.", hint);
   }
 
+  @Test
+  @Config(qualifiers = "zh-rHK")
+  public void textInputHintForChineseHongKong() {
+    SimpleDateFormat sdf = new SimpleDateFormat("dd/MM/yy");
+    String hint = UtcDates.getDefaultTextInputHint(context.getResources(), sdf);
+
+    assertEquals("日/月/年", hint);
+  }
+
   @Test
   public void normalizeTextInputFormat() {
     SimpleDateFormat sdf = new SimpleDateFormat("M/d/y");