Implement customization of date and time format with new FF91+ preferences

"intl.date_time.pattern_override.{date,time}_{short.medium,long,full}", plus

"intl.date_time.pattern_override.connector_short".

See user guide at https://support.mozilla.org/en-US/kb/customize-date-time-formats-thunderbird

As usual, a lot of additional things were changed during the implementation of this feature.

Originally, it is bug 1426907 (5 commits) plus 1674212 plus 1706318. As prerequisite, bug 1669573

(6 commits) plus 1671532 plus 1671695 plus 1681251 are needed (and then two commits of 1672548

to return back a feature which was broken by 1669573-3).

Fortunately, the actually needed changes can be safely applied in a minimal form:

 - get 1426907 commit 5 (https://bugzilla.mozilla.org/show_bug.cgi?id=1426907#c179)

 - drop observer/callback stuff for simplicity (the cost is user have to restart SM

to take changes effect), drop tests

 - add 1674212, drop tests

 - add 1706318 (it just renames pref from 1674212)

 - in the changes added, revert back from "CString" to "String" (since we do not apply 1426907 part 4).

This patch is against SeaMonkey 2.53.8.1 tree. 

--- mozilla/intl/locale/OSPreferences.cpp.orig	2020-10-20 22:17:58.000000000 +0300

+++ mozilla/intl/locale/OSPreferences.cpp	2021-08-23 21:32:05.586135214 +0300

@@ -226,16 +226,136 @@ OSPreferences::GetDateTimeSkeletonForSty

     return false;

   }

   aRetVal.Assign((const char16_t*)skeleton, skelsize);

   return true;

 }

 /**

+ * This method checks for preferences that override the defaults

+ */

+bool OSPreferences::OverrideDateTimePattern(DateTimeFormatStyle aDateStyle,

+                                            DateTimeFormatStyle aTimeStyle,

+                                            const nsACString& aLocale,

+                                            nsAString& aRetVal) {

+  const auto PrefToMaybeString = [](const char* pref) -> Maybe<nsAutoString> {

+    nsAutoString value;

+    nsresult nr = Preferences::GetString(pref, value);

+    if (NS_FAILED(nr) || value.IsEmpty()) {

+      return Nothing();

+    }

+    return Some(std::move(value));

+  };

+

+  Maybe<nsAutoString> timeSkeleton;

+  switch (aTimeStyle) {

+    case DateTimeFormatStyle::Short:

+      timeSkeleton =

+          PrefToMaybeString("intl.date_time.pattern_override.time_short");

+      break;

+    case DateTimeFormatStyle::Medium:

+      timeSkeleton =

+          PrefToMaybeString("intl.date_time.pattern_override.time_medium");

+      break;

+    case DateTimeFormatStyle::Long:

+      timeSkeleton =

+          PrefToMaybeString("intl.date_time.pattern_override.time_long");

+      break;

+    case DateTimeFormatStyle::Full:

+      timeSkeleton =

+          PrefToMaybeString("intl.date_time.pattern_override.time_full");

+      break;

+    default:

+      break;

+  }

+

+  Maybe<nsAutoString> dateSkeleton;

+  switch (aDateStyle) {

+    case DateTimeFormatStyle::Short:

+      dateSkeleton =

+          PrefToMaybeString("intl.date_time.pattern_override.date_short");

+      break;

+    case DateTimeFormatStyle::Medium:

+      dateSkeleton =

+          PrefToMaybeString("intl.date_time.pattern_override.date_medium");

+      break;

+    case DateTimeFormatStyle::Long:

+      dateSkeleton =

+          PrefToMaybeString("intl.date_time.pattern_override.date_long");

+      break;

+    case DateTimeFormatStyle::Full:

+      dateSkeleton =

+          PrefToMaybeString("intl.date_time.pattern_override.date_full");

+      break;

+    default:

+      break;

+  }

+

+  nsAutoCString locale;

+  if (aLocale.IsEmpty()) {

+    AutoTArray<nsCString, 10> regionalPrefsLocales;

+    LocaleService::GetInstance()->GetRegionalPrefsLocales(regionalPrefsLocales);

+    locale.Assign(regionalPrefsLocales[0]);

+  } else {

+    locale.Assign(aLocale);

+  }

+

+  const auto FillConnectorPattern = [&locale](

+                                        const nsAutoString& datePattern,

+                                        const nsAutoString& timePattern) {

+    nsAutoString pattern;

+    GetDateTimeConnectorPattern(nsDependentCString(locale.get()), pattern);

+    int32_t index = pattern.Find("{1}");

+    if (index != kNotFound) {

+      pattern.Replace(index, 3, datePattern);

+    }

+    index = pattern.Find("{0}");

+    if (index != kNotFound) {

+      pattern.Replace(index, 3, timePattern);

+    }

+    return pattern;

+  };

+

+  if (timeSkeleton && dateSkeleton) {

+    aRetVal.Assign(FillConnectorPattern(*dateSkeleton, *timeSkeleton));

+  } else if (timeSkeleton) {

+    if (aDateStyle != DateTimeFormatStyle::None) {

+      nsAutoString pattern;

+      if (!ReadDateTimePattern(aDateStyle, DateTimeFormatStyle::None, aLocale,

+                               pattern) &&

+          !GetDateTimePatternForStyle(aDateStyle, DateTimeFormatStyle::None,

+                                      aLocale, pattern)) {

+        return false;

+      }

+      aRetVal.Assign(FillConnectorPattern(pattern, *timeSkeleton));

+    } else {

+      aRetVal.Assign(*timeSkeleton);

+    }

+  } else if (dateSkeleton) {

+    if (aTimeStyle != DateTimeFormatStyle::None) {

+      nsAutoString pattern;

+      if (!ReadDateTimePattern(DateTimeFormatStyle::None, aTimeStyle, aLocale,

+                               pattern) &&

+          !GetDateTimePatternForStyle(DateTimeFormatStyle::None, aTimeStyle,

+                                      aLocale, pattern)) {

+        return false;

+      }

+      aRetVal.Assign(FillConnectorPattern(*dateSkeleton, pattern));

+    } else {

+      aRetVal.Assign(*dateSkeleton);

+    }

+  } else {

+    return false;

+  }

+

+  return true;

+}

+

+/**

  * This function is a counterpart to GetDateTimeSkeletonForStyle.

  *

  * It takes a skeleton and returns the best available pattern for a given locale

  * that represents the provided skeleton.

  *

  * For example:

  * "Hm" skeleton for "en-US" will return "H:m"

  */

@@ -275,16 +395,27 @@ OSPreferences::GetPatternForSkeleton(con

  *

  * An example output is "{1}, {0}".

  */

 bool

 OSPreferences::GetDateTimeConnectorPattern(const nsACString& aLocale,

                                            nsAString& aRetVal)

 {

   bool result = false;

+

+  // Check for a valid override pref and use that if present.

+  nsAutoString value;

+  nsresult nr = Preferences::GetString(

+      "intl.date_time.pattern_override.connector_short", value);

+  if (NS_SUCCEEDED(nr) && value.Find("{0}") != kNotFound &&

+      value.Find("{1}") != kNotFound) {

+    aRetVal = std::move(value);

+    return true;

+  }

+

   UErrorCode status = U_ZERO_ERROR;

   UDateTimePatternGenerator* pg = udatpg_open(PromiseFlatCString(aLocale).get(), &status);

   if (U_SUCCESS(status)) {

     int32_t resultSize;

     const UChar* value = udatpg_getDateTimeFormat(pg, &resultSize);

     MOZ_ASSERT(resultSize >= 0);

     aRetVal.Assign((char16_t*)value, resultSize);

@@ -409,19 +540,21 @@ OSPreferences::GetDateTimePattern(int32_

   key.AppendInt(aTimeFormatStyle);

   nsString pattern;

   if (mPatternCache.Get(key, &pattern)) {

     aRetVal = pattern;

     return NS_OK;

   }

-  if (!ReadDateTimePattern(dateStyle, timeStyle, aLocale, pattern)) {

-    if (!GetDateTimePatternForStyle(dateStyle, timeStyle, aLocale, pattern)) {

-      return NS_ERROR_FAILURE;

+  if (!OverrideDateTimePattern(dateStyle, timeStyle, aLocale, pattern)) {

+    if (!ReadDateTimePattern(dateStyle, timeStyle, aLocale, pattern)) {

+      if (!GetDateTimePatternForStyle(dateStyle, timeStyle, aLocale, pattern)) {

+        return NS_ERROR_FAILURE;

+      }

     }

   }

   if (mPatternCache.Count() == kMaxCachedPatterns) {

     // Don't allow unlimited cache growth; just throw it away in the case of

     // pathological behavior where a page keeps requesting different formats

     // and locales.

     NS_WARNING("flushing DateTimePattern cache");

--- mozilla/intl/locale/OSPreferences.h.orig	2020-10-20 22:17:58.000000000 +0300

+++ mozilla/intl/locale/OSPreferences.h	2021-08-23 22:07:02.638953273 +0300

@@ -163,16 +163,21 @@ private:

                                   const nsACString& aLocale,

                                   nsAString& aRetVal);

   bool GetDateTimeSkeletonForStyle(DateTimeFormatStyle aDateStyle,

                                    DateTimeFormatStyle aTimeStyle,

                                    const nsACString& aLocale,

                                    nsAString& aRetVal);

+  bool OverrideDateTimePattern(DateTimeFormatStyle aDateStyle,

+                               DateTimeFormatStyle aTimeStyle,

+                               const nsACString& aLocale,

+                               nsAString& aRetVal);

+

   bool GetPatternForSkeleton(const nsAString& aSkeleton,

                              const nsACString& aLocale,

                              nsAString& aRetVal);

   /**

    * This is a host environment specific method that will be implemented

    * separately for each platform.

    *