Index: include/clang/Format/Format.h
===================================================================
--- include/clang/Format/Format.h
+++ include/clang/Format/Format.h
@@ -1685,6 +1685,43 @@
            Standard == R.Standard && TabWidth == R.TabWidth &&
            UseTab == R.UseTab;
   }
+
+  llvm::Optional<FormatStyle> GetLanguageStyle(LanguageKind Language) const;
+
+  // Stores per-language styles. A FormatStyle instance inside has an empty
+  // StyleSet. A FormatStyle instance returned by the Get method has its
+  // StyleSet set to a copy of the originating StyleSet, effectively keeping the
+  // internal representation of that StyleSet alive.
+  //
+  // The memory management and ownership reminds of a birds nest: chicks
+  // leaving the nest take photos of the nest with them.
+  struct FormatStyleSet {
+    typedef std::map<FormatStyle::LanguageKind, FormatStyle> MapType;
+
+    llvm::Optional<FormatStyle> Get(FormatStyle::LanguageKind Language) const;
+
+    // Adds \p Style to this FormatStyleSet. Style must not have an associated
+    // FormatStyleSet.
+    // Style.Language should be different than LK_None. If this FormatStyleSet
+    // already contains an entry for Style.Language, that gets replaced with the
+    // passed Style.
+    void Add(FormatStyle Style);
+
+    // Clears this FormatStyleSet.
+    void Clear();
+
+  private:
+    std::shared_ptr<MapType> Styles;
+  };
+
+  static FormatStyleSet BuildStyleSetFromConfiguration(
+      const FormatStyle &MainStyle,
+      const std::vector<FormatStyle> &ConfigurationStyles);
+
+private:
+  FormatStyleSet StyleSet;
+
+  friend std::error_code parseConfiguration(StringRef Text, FormatStyle *Style);
 };
 
 /// \brief Returns a format style complying with the LLVM coding standards:
@@ -1730,6 +1767,8 @@
 /// Style->Language is used to get the base style, if the ``BasedOnStyle``
 /// option is present.
 ///
+/// The FormatStyleSet of Style is reset.
+///
 /// When ``BasedOnStyle`` is not present, options not present in the YAML
 /// document, are retained in \p Style.
 std::error_code parseConfiguration(StringRef Text, FormatStyle *Style);
Index: lib/Format/Format.cpp
===================================================================
--- lib/Format/Format.cpp
+++ lib/Format/Format.cpp
@@ -859,7 +859,7 @@
   assert(Language != FormatStyle::LK_None);
   if (Text.trim().empty())
     return make_error_code(ParseError::Error);
-
+  Style->StyleSet.Clear();
   std::vector<FormatStyle> Styles;
   llvm::yaml::Input Input(Text);
   // DocumentListTraits<vector<FormatStyle>> uses the context to get default
@@ -888,15 +888,23 @@
   // Look for a suitable configuration starting from the end, so we can
   // find the configuration for the specific language first, and the default
   // configuration (which can only be at slot 0) after it.
+  FormatStyle::FormatStyleSet StyleSet;
+  bool LanguageFound = false;
   for (int i = Styles.size() - 1; i >= 0; --i) {
-    if (Styles[i].Language == Language ||
-        Styles[i].Language == FormatStyle::LK_None) {
-      *Style = Styles[i];
-      Style->Language = Language;
-      return make_error_code(ParseError::Success);
-    }
+    if (Styles[i].Language != FormatStyle::LK_None)
+      StyleSet.Add(Styles[i]);
+    if (Styles[i].Language == Language)
+      LanguageFound = true;
+  }
+  if (!LanguageFound) {
+    if (Styles.empty() || Styles[0].Language != FormatStyle::LK_None)
+      return make_error_code(ParseError::Unsuitable);
+    FormatStyle DefaultStyle = Styles[0];
+    DefaultStyle.Language = Language;
+    StyleSet.Add(std::move(DefaultStyle));
   }
-  return make_error_code(ParseError::Unsuitable);
+  *Style = *StyleSet.Get(Language);
+  return make_error_code(ParseError::Success);
 }
 
 std::string configurationAsText(const FormatStyle &Style) {
@@ -910,6 +918,38 @@
   return Stream.str();
 }
 
+llvm::Optional<FormatStyle>
+FormatStyle::FormatStyleSet::Get(FormatStyle::LanguageKind Language) const {
+  if (!Styles)
+    return None;
+  auto It = Styles->find(Language);
+  if (It == Styles->end())
+    return None;
+  FormatStyle Style = It->second;
+  Style.StyleSet = *this;
+  return Style;
+}
+
+void FormatStyle::FormatStyleSet::Add(FormatStyle Style) {
+  assert(Style.Language != LK_None &&
+         "Cannot add a style for LK_None to a StyleSet");
+  assert(
+      !Style.StyleSet.Styles &&
+      "Cannot add a style associated with an existing StyleSet to a StyleSet");
+  if (!Styles)
+    Styles = std::make_shared<MapType>();
+  (*Styles)[Style.Language] = std::move(Style);
+}
+
+void FormatStyle::FormatStyleSet::Clear() {
+  Styles.reset();
+}
+
+llvm::Optional<FormatStyle>
+FormatStyle::GetLanguageStyle(FormatStyle::LanguageKind Language) const {
+  return StyleSet.Get(Language);
+}
+
 namespace {
 
 class JavaScriptRequoter : public TokenAnalyzer {