Index: clang/lib/Format/UnwrappedLineParser.cpp
===================================================================
--- clang/lib/Format/UnwrappedLineParser.cpp
+++ clang/lib/Format/UnwrappedLineParser.cpp
@@ -491,7 +491,11 @@
   // Keep a stack of positions of lbrace tokens. We will
   // update information about whether an lbrace starts a
   // braced init list or a different block during the loop.
-  SmallVector<FormatToken *, 8> LBraceStack;
+  struct StackEntry {
+    FormatToken *Tok;
+    const FormatToken *PrevTok;
+  };
+  SmallVector<StackEntry, 8> LBraceStack;
   assert(Tok->is(tok::l_brace));
   do {
     // Get next non-comment token.
@@ -521,12 +525,12 @@
       } else {
         Tok->setBlockKind(BK_Unknown);
       }
-      LBraceStack.push_back(Tok);
+      LBraceStack.push_back({Tok, PrevTok});
       break;
     case tok::r_brace:
       if (LBraceStack.empty())
         break;
-      if (LBraceStack.back()->is(BK_Unknown)) {
+      if (LBraceStack.back().Tok->is(BK_Unknown)) {
         bool ProbablyBracedList = false;
         if (Style.Language == FormatStyle::LK_Proto) {
           ProbablyBracedList = NextTok->isOneOf(tok::comma, tok::r_square);
@@ -554,7 +558,7 @@
 
           // If we already marked the opening brace as braced list, the closing
           // must also be part of it.
-          ProbablyBracedList = LBraceStack.back()->is(TT_BracedListLBrace);
+          ProbablyBracedList = LBraceStack.back().Tok->is(TT_BracedListLBrace);
 
           ProbablyBracedList = ProbablyBracedList ||
                                (Style.isJavaScript() &&
@@ -570,8 +574,14 @@
           ProbablyBracedList =
               ProbablyBracedList ||
               NextTok->isOneOf(tok::comma, tok::period, tok::colon,
-                               tok::r_paren, tok::r_square, tok::l_brace,
-                               tok::ellipsis);
+                               tok::r_paren, tok::r_square, tok::ellipsis);
+
+          // Distinguish between braced list in a constructor initializer list
+          // followed by constructor body, or just adjacent blocks.
+          ProbablyBracedList =
+              ProbablyBracedList ||
+              NextTok->is(tok::l_brace) && LBraceStack.back().PrevTok &&
+                  LBraceStack.back().PrevTok->is(tok::identifier);
 
           ProbablyBracedList =
               ProbablyBracedList ||
@@ -595,10 +605,10 @@
         }
         if (ProbablyBracedList) {
           Tok->setBlockKind(BK_BracedInit);
-          LBraceStack.back()->setBlockKind(BK_BracedInit);
+          LBraceStack.back().Tok->setBlockKind(BK_BracedInit);
         } else {
           Tok->setBlockKind(BK_Block);
-          LBraceStack.back()->setBlockKind(BK_Block);
+          LBraceStack.back().Tok->setBlockKind(BK_Block);
         }
       }
       LBraceStack.pop_back();
@@ -615,8 +625,8 @@
     case tok::kw_switch:
     case tok::kw_try:
     case tok::kw___try:
-      if (!LBraceStack.empty() && LBraceStack.back()->is(BK_Unknown))
-        LBraceStack.back()->setBlockKind(BK_Block);
+      if (!LBraceStack.empty() && LBraceStack.back().Tok->is(BK_Unknown))
+        LBraceStack.back().Tok->setBlockKind(BK_Block);
       break;
     default:
       break;
@@ -626,9 +636,9 @@
   } while (Tok->isNot(tok::eof) && !LBraceStack.empty());
 
   // Assume other blocks for all unclosed opening braces.
-  for (FormatToken *LBrace : LBraceStack)
-    if (LBrace->is(BK_Unknown))
-      LBrace->setBlockKind(BK_Block);
+  for (const auto &Entry : LBraceStack)
+    if (Entry.Tok->is(BK_Unknown))
+      Entry.Tok->setBlockKind(BK_Block);
 
   FormatTok = Tokens->setPosition(StoredPosition);
 }
Index: clang/unittests/Format/FormatTest.cpp
===================================================================
--- clang/unittests/Format/FormatTest.cpp
+++ clang/unittests/Format/FormatTest.cpp
@@ -13731,6 +13731,26 @@
                "  struct Dummy {};\n"
                "  f(v);\n"
                "}");
+  verifyFormat("void foo() {\n"
+               "  { // asdf\n"
+               "    { int a; }\n"
+               "  }\n"
+               "  {\n"
+               "    { int b; }\n"
+               "  }\n"
+               "}");
+  verifyFormat("namespace n {\n"
+               "void foo() {\n"
+               "  {\n"
+               "    {\n"
+               "      statement();\n"
+               "      if (false) {\n"
+               "      }\n"
+               "    }\n"
+               "  }\n"
+               "  {}\n"
+               "}\n"
+               "} // namespace n");
 
   // Long lists should be formatted in columns even if they are nested.
   verifyFormat(
Index: clang/unittests/Format/TokenAnnotatorTest.cpp
===================================================================
--- clang/unittests/Format/TokenAnnotatorTest.cpp
+++ clang/unittests/Format/TokenAnnotatorTest.cpp
@@ -40,6 +40,8 @@
   EXPECT_EQ((FormatTok)->getType(), Type) << *(FormatTok)
 #define EXPECT_TOKEN_PRECEDENCE(FormatTok, Prec)                               \
   EXPECT_EQ((FormatTok)->getPrecedence(), Prec) << *(FormatTok)
+#define EXPECT_BRACE_KIND(FormatTok, Kind)                                     \
+  EXPECT_EQ(FormatTok->getBlockKind(), Kind) << *(FormatTok)
 #define EXPECT_TOKEN(FormatTok, Kind, Type)                                    \
   do {                                                                         \
     EXPECT_TOKEN_KIND(FormatTok, Kind);                                        \
@@ -1783,6 +1785,22 @@
   EXPECT_TOKEN(Tokens[3], tok::colon, TT_CaseLabelColon);
 }
 
+TEST_F(TokenAnnotatorTest, UnderstandsNestedBlocks) {
+  // The closing braces are not annotated.  It doesn't seem to cause a
+  // problem.  So we only test for the opening braces.
+  auto Tokens = annotate("{\n"
+                         "  {\n"
+                         "    { int a = 0; }\n"
+                         "  }\n"
+                         "  {}\n"
+                         "}");
+  ASSERT_EQ(Tokens.size(), 14u) << Tokens;
+  EXPECT_BRACE_KIND(Tokens[0], BK_Block);
+  EXPECT_BRACE_KIND(Tokens[1], BK_Block);
+  EXPECT_BRACE_KIND(Tokens[2], BK_Block);
+  EXPECT_BRACE_KIND(Tokens[10], BK_Block);
+}
+
 } // namespace
 } // namespace format
 } // namespace clang