Improve error handling when no format is resolved

lib/cldr/backend/date_time.ex

@@ -247,7 +247,7 @@ defmodule Cldr.DateAndTime.Backend do
             # CLDR defined format.
             iex> #{inspect(__MODULE__)}.to_string(%{year: 2024, day: 3}, locale: "fr")
             {:error,
-             {Cldr.DateTime.UnresolvedFormat, "No available format resolved for \\"dy\\""}}
+             {Cldr.DateTime.UnresolvedFormat, "No available format resolved for :dy"}}
 
         """
         @spec to_string(Cldr.Calendar.any_date_time(), Keyword.t()) ::
@@ -408,7 +408,7 @@ defmodule Cldr.DateAndTime.Backend do
             # CLDR defined format.
             iex> #{inspect(__MODULE__)}.to_string(%{minute: 11})
             {:error,
-             {Cldr.DateTime.UnresolvedFormat, "No available format resolved for \\"m\\""}}
+             {Cldr.DateTime.UnresolvedFormat, "No available format resolved for :m"}}
 
         """
         @spec to_string(Cldr.Calendar.any_date_time(), Keyword.t()) ::

lib/cldr/date.ex

@@ -118,7 +118,7 @@ defmodule Cldr.Date do
       # CLDR-defined format.
       iex> Cldr.Date.to_string(%{year: 2024, day: 3}, MyApp.Cldr, locale: "fr")
       {:error,
-       {Cldr.DateTime.UnresolvedFormat, "No available format resolved for \\"dy\\""}}
+       {Cldr.DateTime.UnresolvedFormat, "No available format resolved for :dy"}}
 
   """
   @spec to_string(Cldr.Calendar.any_date_time(), Cldr.backend() | Keyword.t(), Keyword.t()) ::
@@ -464,9 +464,7 @@ defmodule Cldr.Date do
     if Map.has_key?(available_formats, format) do
       Map.fetch(available_formats, format)
     else
-      with {:ok, match} <- Cldr.DateTime.Format.best_match(format, locale, calendar, backend) do
-        {:ok, Map.fetch!(available_formats, match)}
-      end
+      resolve_format(format, available_formats, locale, calendar, backend)
     end
   end
 
@@ -478,6 +476,20 @@ defmodule Cldr.Date do
     {:ok, format_string}
   end
 
+  @doc false
+  def resolve_format(format, available_formats, locale, calendar, backend) do
+    with {:ok, match} <- Cldr.DateTime.Format.best_match(format, locale, calendar, backend),
+         {:ok, format} <- Map.fetch(available_formats, match) do
+      {:ok, format}
+    else
+      :error ->
+        {:error, Cldr.DateTime.Format.no_format_resolved_error(format)}
+
+      other ->
+        other
+    end
+  end
+
   defp error_return(map, requirements) do
     requirements =
       requirements

lib/cldr/format/date_time_format.ex

@@ -632,13 +632,13 @@ defmodule Cldr.DateTime.Format do
         ) :: {:ok, format_id()} | {:error, {module(), String.t()}}
 
   def best_match(
-        skeleton,
+        original_skeleton,
         locale \\ Cldr.get_locale(),
         calendar \\ Cldr.Calendar.default_cldr_calendar(),
         backend \\ Cldr.Date.default_backend()
       ) do
     with {:ok, locale} <- Cldr.validate_locale(locale, backend),
-         skeleton = to_string(skeleton),
+         skeleton = to_string(original_skeleton),
          {:ok, skeleton} <- put_preferred_time_symbols(skeleton, locale),
          {:ok, skeleton_tokens} <- Compiler.tokenize_skeleton(skeleton) do
       # match_with_day_periods? =
@@ -663,18 +663,22 @@ defmodule Cldr.DateTime.Format do
 
       case candidates do
         [] ->
-          {:error,
-           {
-             Cldr.DateTime.UnresolvedFormat,
-             "No available format resolved for #{inspect(skeleton)}"
-           }}
+          {:error, no_format_resolved_error(original_skeleton)}
 
         [{format_id, _} | _rest] ->
           {:ok, format_id}
       end
     end
   end
 
+  @doc false
+  def no_format_resolved_error(skeleton) do
+    {
+      Cldr.DateTime.UnresolvedFormat,
+      "No available format resolved for #{inspect(skeleton)}"
+    }
+  end
+
   # https://www.unicode.org/reports/tr35/tr35-dates.html#Matching_Skeletons
   # For skeleton and id fields with symbols representing the same type (year, month, day, etc):
   # Most symbols have a small distance from each other.
@@ -785,6 +789,9 @@ defmodule Cldr.DateTime.Format do
         when different_but_compatible({symbol_a, count_a}, {symbol_b, count_b}) and
                different_types({symbol_a, count_a}, {symbol_b, count_b}) ->
           acc + abs(count_a - count_b) + 10
+
+        _other_a, _other_b, acc ->
+          acc + 10
       end)
 
     {token_id, distance}

lib/cldr/time.ex

@@ -125,7 +125,7 @@ defmodule Cldr.Time do
       # CLDR-defined format.
       iex> Cldr.Time.to_string(%{minute: 11})
       {:error,
-       {Cldr.DateTime.UnresolvedFormat, "No available format resolved for \\"m\\""}}
+       {Cldr.DateTime.UnresolvedFormat, "No available format resolved for :m"}}
 
   """
   @spec to_string(map, Cldr.backend() | Keyword.t(), Keyword.t()) ::
@@ -347,9 +347,7 @@ defmodule Cldr.Time do
     if Map.has_key?(available_formats, format) do
       Map.fetch(available_formats, format)
     else
-      with {:ok, match} <- Cldr.DateTime.Format.best_match(format, locale, calendar, backend) do
-        {:ok, Map.fetch!(available_formats, match)}
-      end
+      resolve_format(format, available_formats, locale, calendar, backend)
     end
   end
 
@@ -361,6 +359,9 @@ defmodule Cldr.Time do
     {:ok, format_string}
   end
 
+  @doc false
+  defdelegate resolve_format(format, available_formats, locale, calendar, backend), to: Cldr.Date
+
   @doc """
   Returns a map of the standard time formats for a given
   locale and calendar.

test/partial_date_times_test.exs

@@ -15,7 +15,7 @@ defmodule Cldr.DateTime.PartialTest do
 
     assert Cldr.Date.to_string(%{year: 3, day: 5}) ==
       {:error,
-       {Cldr.DateTime.UnresolvedFormat, "No available format resolved for \"dy\""}}
+       {Cldr.DateTime.UnresolvedFormat, "No available format resolved for :dy"}}
   end
 
   test "Partial Times" do
@@ -43,7 +43,7 @@ defmodule Cldr.DateTime.PartialTest do
 
     assert Cldr.Time.to_string(%{hour: 23, second: 45}) ==
       {:error,
-        {Cldr.DateTime.UnresolvedFormat, "No available format resolved for \"sh\""}}
+        {Cldr.DateTime.UnresolvedFormat, "No available format resolved for :sh"}}
 
     assert Cldr.Time.to_string(%{hour: 23, second: 45}, format: "h:m:s") ==
       {:error,
@@ -58,7 +58,7 @@ defmodule Cldr.DateTime.PartialTest do
 
     assert Cldr.DateTime.to_string(%{year: 2024, minute: 10}) ==
       {:error,
-        {Cldr.DateTime.UnresolvedFormat, "No available format resolved for \"m\""}}
+        {Cldr.DateTime.UnresolvedFormat, "No available format resolved for :m"}}
 
   end