Automatic resConfig.

- Test to ensure language_entries list matches exactly the available resources.

build.gradle

@@ -149,6 +149,7 @@ dependencies {
     testImplementation 'org.powermock:powermock-module-junit4-rule:1.6.1'
     testImplementation 'org.powermock:powermock-classloading-xstream:1.6.1'
 
+    testImplementation 'androidx.test:core:1.1.1-alpha02'
     androidTestImplementation 'com.android.support:multidex:1.0.3'
     androidTestImplementation 'com.android.support:multidex-instrumentation:1.0.3'
     androidTestImplementation 'com.google.dexmaker:dexmaker:1.2'
@@ -324,10 +325,13 @@ android {
         buildConfigField "boolean", "DEV_BUILD", "false"
         buildConfigField "String", "MRENCLAVE", "\"cd6cfc342937b23b1bdd3bbf9721aa5615ac9ff50a75c5527d441cd3276826c9\""
         buildConfigField "String", "UNIDENTIFIED_SENDER_TRUST_ROOT", "\"BXu6QIKVz5MA8gstzfOgRQGqyLqOwNKHL6INkv3IHWMF\""
+        buildConfigField "String[]", "LANGUAGES", "new String[]{\"" + autoResConfig().collect { s -> s.replace('-r', '_') }.join('", "') + '"}'
 
         ndk {
             abiFilters "armeabi", "armeabi-v7a", "x86"
         }
+
+        resConfigs autoResConfig()
     }
 
     compileOptions {
@@ -510,3 +514,16 @@ def getLastCommitTimestamp() {
         return os.toString() + "000"
     }
 }
+
+/**
+ * Discovers supported languages listed as under the res/values- directory.
+ */
+static def autoResConfig() {
+    def files = new ArrayList<String>()
+    def root = new File('res')
+    root.eachFile { f -> files.add(f.name) }
+    ['en'] + files.collect { f -> f =~ /^values-([a-z]{2}(-r[A-Z]{2})?)$/ }
+         .findAll { matcher -> matcher.find() }
+         .collect { matcher -> matcher.group(1) }
+         .sort()
+}

test/unitTest/java/org/thoughtcrime/securesms/l10n/LanguageResourcesTest.java

@@ -0,0 +1,84 @@
+package org.thoughtcrime.securesms.l10n;
+
+import android.app.Application;
+import android.content.res.Resources;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.robolectric.RobolectricTestRunner;
+import org.robolectric.annotation.Config;
+import org.thoughtcrime.securesms.BuildConfig;
+import org.thoughtcrime.securesms.R;
+
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+
+import androidx.test.core.app.ApplicationProvider;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.fail;
+
+@RunWith(RobolectricTestRunner.class)
+@Config(manifest = Config.NONE, application = Application.class)
+public final class LanguageResourcesTest {
+
+  @Test
+  public void language_entries_match_language_values_in_length() {
+    Resources resources = ApplicationProvider.getApplicationContext().getResources();
+    String[]  values    = resources.getStringArray(R.array.language_values);
+    String[]  entries   = resources.getStringArray(R.array.language_entries);
+    assertEquals(values.length, entries.length);
+  }
+
+  @Test
+  public void language_options_matches_available_resources() {
+    Set<String> languageEntries = languageEntries();
+    Set<String> foundResources  = buildConfigResources();
+    if (!languageEntries.equals(foundResources)) {
+      assertSubset(foundResources, languageEntries, "Missing language_entries for resources");
+      assertSubset(languageEntries, foundResources, "Missing resources for language_entries");
+      fail("Unexpected");
+    }
+  }
+
+  private static Set<String> languageEntries() {
+    Resources resources = ApplicationProvider.getApplicationContext().getResources();
+    String[]  values    = resources.getStringArray(R.array.language_values);
+
+    List<String> tail = Arrays.asList(values).subList(1, values.length);
+    Set<String>  set  = new HashSet<>(tail);
+
+    assertEquals("First is not the default", "zz", values[0]);
+    assertEquals("List contains duplicates", tail.size(), set.size());
+    return set;
+  }
+
+  private static Set<String> buildConfigResources() {
+    Set<String> set = new HashSet<>();
+    Collections.addAll(set, BuildConfig.LANGUAGES);
+    assertEquals("List contains duplicates", BuildConfig.LANGUAGES.length, set.size());
+    return set;
+  }
+
+  /**
+   * Fails if "a" is not a subset of "b", lists the additional values found in "a"
+   */
+  private static void assertSubset(Set<String> a, Set<String> b, String message) {
+    Set<String> delta = subtract(a, b);
+    if (!delta.isEmpty()) {
+      fail(message + ": " + String.join(", ", delta));
+    }
+  }
+
+  /**
+   * Set a - Set b
+   */
+  private static Set<String> subtract(Set<String> a, Set<String> b) {
+    Set<String> set = new HashSet<>(a);
+    set.removeAll(b);
+    return set;
+  }
+}