Added support for hierarchical culture fallback:

- Enabled by default and configured by RequestLocalizationOptions.FallbackToAncestorCulture/FallbackToAncestorUICulture
- Tries all candidate cultures first before trimming the list to parents and trying again, until a match is found, depth limit is reached, or none is found
- Updated functional tests to cover fallback case
- #112

src/Microsoft.AspNet.Localization/RequestLocalizationMiddleware.cs

@@ -18,6 +18,8 @@ namespace Microsoft.AspNet.Localization
     /// </summary>
     public class RequestLocalizationMiddleware
     {
+        private static readonly int MaxCultureFallbackDepth = 5;
+
         private readonly RequestDelegate _next;
         private readonly RequestLocalizationOptions _options;
 
@@ -27,9 +29,7 @@ namespace Microsoft.AspNet.Localization
         /// <param name="next">The <see cref="RequestDelegate"/> representing the next middleware in the pipeline.</param>
         /// <param name="options">The <see cref="RequestLocalizationOptions"/> representing the options for the
         /// <see cref="RequestLocalizationMiddleware"/>.</param>
-        public RequestLocalizationMiddleware(
+        public RequestLocalizationMiddleware(RequestDelegate next, RequestLocalizationOptions options)
-            RequestDelegate next,
-            RequestLocalizationOptions options)
         {
             if (next == null)
             {
@@ -75,22 +75,32 @@ namespace Microsoft.AspNet.Localization
                         CultureInfo uiCultureInfo = null;
                         if (_options.SupportedCultures != null)
                         {
-                            cultureInfo = GetCultureInfo(cultures, _options.SupportedCultures);
+                            cultureInfo = GetCultureInfo(
+                                cultures,
+                                _options.SupportedCultures,
+                                _options.FallbackToAncestorCulture,
+                                currentDepth: 0);
                         }
 
                         if (_options.SupportedUICultures != null)
                         {
-                            uiCultureInfo = GetCultureInfo(uiCultures, _options.SupportedUICultures);
+                            uiCultureInfo = GetCultureInfo(
+                                uiCultures,
+                                _options.SupportedUICultures,
+                                _options.FallbackToAncestorUICulture,
+                                currentDepth: 0);
                         }
 
                         if (cultureInfo == null && uiCultureInfo == null)
                         {
                             continue;
                         }
+
                         if (cultureInfo == null && uiCultureInfo != null)
                         {
                             cultureInfo = _options.DefaultRequestCulture.Culture;
                         }
+
                         if (cultureInfo != null && uiCultureInfo == null)
                         {
                             uiCultureInfo = _options.DefaultRequestCulture.UICulture;
@@ -126,15 +136,19 @@ namespace Microsoft.AspNet.Localization
 #endif
         }
 
-        private CultureInfo GetCultureInfo(IList<string> cultures, IList<CultureInfo> supportedCultures)
+        private static CultureInfo GetCultureInfo(
+            IList<string> cultureNames,
+            IList<CultureInfo> supportedCultures,
+            bool fallbackToAncestorCulture,
+            int currentDepth)
         {
-            foreach (var culture in cultures)
+            foreach (var cultureName in cultureNames)
             {
                 // Allow empty string values as they map to InvariantCulture, whereas null culture values will throw in
                 // the CultureInfo ctor
-                if (culture != null)
+                if (cultureName != null)
                 {
-                    var cultureInfo = CultureInfoCache.GetCultureInfo(culture, supportedCultures);
+                    var cultureInfo = CultureInfoCache.GetCultureInfo(cultureName, supportedCultures);
                     if (cultureInfo != null)
                     {
                         return cultureInfo;
@@ -142,6 +156,39 @@ namespace Microsoft.AspNet.Localization
                 }
             }
 
+            if (fallbackToAncestorCulture & currentDepth < MaxCultureFallbackDepth)
+            {
+                // Walk backwards through the culture list and remove any root cultures (those with no parent)
+                for (var i = cultureNames.Count - 1; i >= 0; i--)
+                {
+                    var cultureName = cultureNames[i];
+                    if (cultureName != null)
+                    {
+                        var lastIndexOfHyphen = cultureName.LastIndexOf('-');
+                        if (lastIndexOfHyphen > 0)
+                        {
+                            // Trim the trailing section from the culture name, e.g. "fr-FR" becomes "fr"
+                            cultureNames[i] = cultureName.Substring(0, lastIndexOfHyphen);
+                        }
+                        else
+                        {
+                            // The culture had no sections left to trim so remove it from the list of candidates
+                            cultureNames.RemoveAt(i);
+                        }
+                    }
+                    else
+                    {
+                        // Culture name was null so just remove it
+                        cultureNames.RemoveAt(i);
+                    }
+                }
+
+                if (cultureNames.Count > 0)
+                {
+                    return GetCultureInfo(cultureNames, supportedCultures, fallbackToAncestorCulture, currentDepth + 1);
+                }
+            }
+
             return null;
         }
     }

src/Microsoft.AspNet.Localization/RequestLocalizationOptions.cs

@@ -50,6 +50,33 @@ namespace Microsoft.AspNet.Localization
             }
         }
 
+        /// <summary>
+        /// Gets or sets a value indicating whether to set a request culture to an ancestor culture in the case the
+        /// culture determined by the configured <see cref="IRequestCultureProvider"/>s is not in the
+        /// <see cref="SupportedCultures"/> list but an ancestor culture is.
+        /// Defaults to <c>true</c>;
+        /// </summary>
+        /// <example>
+        /// If this property is <c>true</c> and the application is configured to support the culture "fr", but not the
+        /// culture "fr-FR", and a configured <see cref="IRequestCultureProvider"/> determines a request's culture is
+        /// "fr-FR", then the request's culture will be set to the culture "fr", as it is an ancestor of "fr-FR".
+        /// </example>
+        public bool FallbackToAncestorCulture { get; set; } = true;
+
+        /// <summary>
+        /// Gets or sets a value indicating whether to set a request UI culture to an ancestor culture in the case the
+        /// UI culture determined by the configured <see cref="IRequestCultureProvider"/>s is not in the
+        /// <see cref="SupportedUICultures"/> list but an ancestor culture is.
+        /// Defaults to <c>true</c>;
+        /// </summary>
+        /// <example>
+        /// If this property is <c>true</c> and the application is configured to support the UI culture "fr", but not
+        /// the UI culture "fr-FR", and a configured <see cref="IRequestCultureProvider"/> determines a request's UI
+        /// culture is "fr-FR", then the request's UI culture will be set to the culture "fr", as it is an ancestor of
+        /// "fr-FR".
+        /// </example>
+        public bool FallbackToAncestorUICulture { get; set; } = true;
+
         /// <summary>
         /// The cultures supported by the application. The <see cref="RequestLocalizationMiddleware"/> will only set
         /// the current request culture to an entry in this list.

test/Microsoft.AspNet.Localization.FunctionalTests/LocalizationTest.cs

@@ -30,6 +30,46 @@ namespace Microsoft.AspNet.Localization.FunctionalTests
                 "Bonjour from StartupResourcesInFolder Bonjour from Test in resources folder Bonjour from Customer in resources folder");
         }
 
+        [ConditionalTheory]
+        [OSSkipCondition(OperatingSystems.Linux)]
+        [OSSkipCondition(OperatingSystems.MacOSX)]
+        [InlineData(RuntimeFlavor.Clr, "http://localhost:5070/", RuntimeArchitecture.x86)]
+        [InlineData(RuntimeFlavor.CoreClr, "http://localhost:5071/", RuntimeArchitecture.x86)]
+        public Task Localization_ResourcesInFolder_ReturnLocalizedValue_WithCultureFallback_Windows(
+            RuntimeFlavor runtimeFlavor,
+            string applicationBaseUrl,
+            RuntimeArchitecture runtimeArchitechture)
+        {
+            var testRunner = new TestRunner();
+            return testRunner.RunTestAndVerifyResponse(
+                runtimeFlavor,
+                runtimeArchitechture,
+                applicationBaseUrl,
+                "ResourcesInFolder",
+                "fr-FR-test",
+                "Bonjour from StartupResourcesInFolder Bonjour from Test in resources folder Bonjour from Customer in resources folder");
+        }
+
+        [ConditionalTheory]
+        [OSSkipCondition(OperatingSystems.Linux)]
+        [OSSkipCondition(OperatingSystems.MacOSX)]
+        [InlineData(RuntimeFlavor.Clr, "http://localhost:5070/", RuntimeArchitecture.x86)]
+        [InlineData(RuntimeFlavor.CoreClr, "http://localhost:5071/", RuntimeArchitecture.x86)]
+        public Task Localization_ResourcesInFolder_ReturnNonLocalizedValue_CultureHierarchyTooDeep_Windows(
+            RuntimeFlavor runtimeFlavor,
+            string applicationBaseUrl,
+            RuntimeArchitecture runtimeArchitechture)
+        {
+            var testRunner = new TestRunner();
+            return testRunner.RunTestAndVerifyResponse(
+                runtimeFlavor,
+                runtimeArchitechture,
+                applicationBaseUrl,
+                "ResourcesInFolder",
+                "fr-FR-test-again-too-deep-to-work",
+                "Hello Hello Hello");
+        }
+
         [ConditionalFact]
         [OSSkipCondition(OperatingSystems.Windows)]
         [FrameworkSkipCondition(RuntimeFrameworks.CoreCLR)]
@@ -45,6 +85,21 @@ namespace Microsoft.AspNet.Localization.FunctionalTests
                 "Bonjour from StartupResourcesInFolder Bonjour from Test in resources folder Bonjour from Customer in resources folder");
         }
 
+        [ConditionalFact]
+        [OSSkipCondition(OperatingSystems.Windows)]
+        [FrameworkSkipCondition(RuntimeFrameworks.CoreCLR)]
+        public Task Localization_ResourcesInFolder_ReturnLocalizedValue_WithCultureFallback_Mono()
+        {
+            var testRunner = new TestRunner();
+            return testRunner.RunTestAndVerifyResponse(
+                RuntimeFlavor.Mono,
+                RuntimeArchitecture.x86,
+                "http://localhost:5072",
+                "ResourcesInFolder",
+                "fr-FR-test",
+                "Bonjour from StartupResourcesInFolder Bonjour from Test in resources folder Bonjour from Customer in resources folder");
+        }
+
         [ConditionalFact]
         [OSSkipCondition(OperatingSystems.Windows)]
         [FrameworkSkipCondition(RuntimeFrameworks.Mono)]
@@ -60,6 +115,21 @@ namespace Microsoft.AspNet.Localization.FunctionalTests
                 "Bonjour from StartupResourcesInFolder Bonjour from Test in resources folder Bonjour from Customer in resources folder");
         }
 
+        [ConditionalFact]
+        [OSSkipCondition(OperatingSystems.Windows)]
+        [FrameworkSkipCondition(RuntimeFrameworks.Mono)]
+        public Task Localization_ResourcesInFolder_ReturnLocalizedValue_WithCultureFallback_CoreCLR_NonWindows()
+        {
+            var testRunner = new TestRunner();
+            return testRunner.RunTestAndVerifyResponse(
+                RuntimeFlavor.CoreClr,
+                RuntimeArchitecture.x64,
+                "http://localhost:5073/",
+                "ResourcesInFolder",
+                "fr-FR-test",
+                "Bonjour from StartupResourcesInFolder Bonjour from Test in resources folder Bonjour from Customer in resources folder");
+        }
+
         [ConditionalTheory]
         [OSSkipCondition(OperatingSystems.Linux)]
         [OSSkipCondition(OperatingSystems.MacOSX)]