Index: lib/Format/TokenAnnotator.cpp
===================================================================
--- lib/Format/TokenAnnotator.cpp
+++ lib/Format/TokenAnnotator.cpp
@@ -592,7 +592,8 @@
           return false;
       }
     }
-    return true;
+    // There are no top-level unbalanced braces in text protos.
+    return Style.Language != FormatStyle::LK_TextProto;
   }
 
   void updateParameterCount(FormatToken *Left, FormatToken *Current) {
@@ -712,6 +713,11 @@
       } else if (Contexts.back().ContextKind == tok::l_paren) {
         Tok->Type = TT_InlineASMColon;
       }
+      // Detects trailing pieces like key:
+      if ((Style.Language == FormatStyle::LK_Proto ||
+           Style.Language == FormatStyle::LK_TextProto) &&
+          !CurrentToken)
+        return false;
       break;
     case tok::pipe:
     case tok::amp:
@@ -798,6 +804,10 @@
           if (Previous && Previous->Type != TT_DictLiteral)
             Previous->Type = TT_SelectorName;
         }
+      } else if (Style.Language == FormatStyle::LK_TextProto ||
+                 Style.Language == FormatStyle::LK_Proto) {
+        // In TT_Proto and TT_TextProto, tok::less cannot be a binary operator.
+        return false;
       } else {
         Tok->Type = TT_BinaryOperator;
         NonTemplateLess.insert(Tok);
@@ -809,13 +819,16 @@
     case tok::r_square:
       return false;
     case tok::r_brace:
-      // Lines can start with '}'.
-      if (Tok->Previous)
+      // Lines can start with '}' except in text protos.
+      if (Tok->Previous || Style.Language == FormatStyle::LK_TextProto)
         return false;
       break;
     case tok::greater:
-      if (Style.Language != FormatStyle::LK_TextProto)
-        Tok->Type = TT_BinaryOperator;
+      // In protos and text protos tok::greater cannot be a binary operator.
+      if (Style.Language == FormatStyle::LK_Proto ||
+          Style.Language == FormatStyle::LK_TextProto)
+        return false;
+      Tok->Type = TT_BinaryOperator;
       break;
     case tok::kw_operator:
       if (Style.Language == FormatStyle::LK_TextProto ||
Index: unittests/Format/FormatTestProto.cpp
===================================================================
--- unittests/Format/FormatTestProto.cpp
+++ unittests/Format/FormatTestProto.cpp
@@ -18,13 +18,21 @@
 namespace format {
 
 class FormatTestProto : public ::testing::Test {
+  enum StatusCheck { SC_ExpectComplete, SC_ExpectIncomplete };
+
 protected:
   static std::string format(llvm::StringRef Code, unsigned Offset,
-                            unsigned Length, const FormatStyle &Style) {
+                            unsigned Length, const FormatStyle &Style,
+                            StatusCheck CheckComplete = SC_ExpectComplete) {
     DEBUG(llvm::errs() << "---\n");
     DEBUG(llvm::errs() << Code << "\n\n");
     std::vector<tooling::Range> Ranges(1, tooling::Range(Offset, Length));
-    tooling::Replacements Replaces = reformat(Style, Code, Ranges);
+    FormattingAttemptStatus Status;
+    tooling::Replacements Replaces =
+        reformat(Style, Code, Ranges, "<stdin>", &Status);
+    bool ExpectedCompleteFormat = CheckComplete == SC_ExpectComplete;
+    EXPECT_EQ(ExpectedCompleteFormat, Status.FormatComplete)
+        << Code << "\n\n";
     auto Result = applyAllReplacements(Code, Replaces);
     EXPECT_TRUE(static_cast<bool>(Result));
     DEBUG(llvm::errs() << "\n" << *Result << "\n\n");
@@ -41,6 +49,12 @@
     EXPECT_EQ(Code.str(), format(Code)) << "Expected code is not stable";
     EXPECT_EQ(Code.str(), format(test::messUp(Code)));
   }
+
+  static void verifyIncompleteFormat(llvm::StringRef Code) {
+    FormatStyle Style = getGoogleStyle(FormatStyle::LK_Proto);
+    EXPECT_EQ(Code.str(),
+              format(Code, 0, Code.size(), Style, SC_ExpectIncomplete));
+  }
 };
 
 TEST_F(FormatTestProto, FormatsMessages) {
@@ -492,5 +506,12 @@
                "};");
 }
 
+TEST_F(FormatTestProto, IncompleteFormat) {
+  verifyIncompleteFormat("option (");
+  verifyIncompleteFormat("option (MyProto.options) = { bbbbbbbbb:");
+  verifyIncompleteFormat("option (MyProto.options) = { bbbbbbbbb: <\n");
+  verifyIncompleteFormat("option (MyProto.options) = { bbbbbbbbb: [\n");
+}
+
 } // end namespace tooling
 } // end namespace clang
Index: unittests/Format/FormatTestTextProto.cpp
===================================================================
--- unittests/Format/FormatTestTextProto.cpp
+++ unittests/Format/FormatTestTextProto.cpp
@@ -19,12 +19,20 @@
 
 class FormatTestTextProto : public ::testing::Test {
 protected:
+  enum StatusCheck { SC_ExpectComplete, SC_ExpectIncomplete };
+
   static std::string format(llvm::StringRef Code, unsigned Offset,
-                            unsigned Length, const FormatStyle &Style) {
+                            unsigned Length, const FormatStyle &Style,
+                            StatusCheck CheckComplete = SC_ExpectComplete) {
     DEBUG(llvm::errs() << "---\n");
     DEBUG(llvm::errs() << Code << "\n\n");
     std::vector<tooling::Range> Ranges(1, tooling::Range(Offset, Length));
-    tooling::Replacements Replaces = reformat(Style, Code, Ranges);
+    FormattingAttemptStatus Status;
+    tooling::Replacements Replaces =
+        reformat(Style, Code, Ranges, "<stdin>", &Status);
+    bool ExpectedCompleteFormat = CheckComplete == SC_ExpectComplete;
+    EXPECT_EQ(ExpectedCompleteFormat, Status.FormatComplete)
+        << Code << "\n\n";
     auto Result = applyAllReplacements(Code, Replaces);
     EXPECT_TRUE(static_cast<bool>(Result));
     DEBUG(llvm::errs() << "\n" << *Result << "\n\n");
@@ -45,6 +53,12 @@
     Style.ColumnLimit = 60; // To make writing tests easier.
     verifyFormat(Code, Style);
   }
+
+  static void verifyIncompleteFormat(llvm::StringRef Code) {
+    FormatStyle Style = getGoogleStyle(FormatStyle::LK_TextProto);
+    EXPECT_EQ(Code.str(),
+              format(Code, 0, Code.size(), Style, SC_ExpectIncomplete));
+  }
 };
 
 TEST_F(FormatTestTextProto, KeepsTopLevelEntriesFittingALine) {
@@ -495,5 +509,38 @@
                "}", Style);
 }
 
+TEST_F(FormatTestTextProto, IncompleteFormat) {
+  verifyIncompleteFormat("data {");
+  verifyIncompleteFormat("data <");
+  verifyIncompleteFormat("data [");
+  verifyIncompleteFormat("data: {");
+  verifyIncompleteFormat("data: <");
+  verifyIncompleteFormat("data: [");
+  verifyIncompleteFormat("key:");
+  verifyIncompleteFormat("key:}");
+  verifyIncompleteFormat("key: ]");
+  verifyIncompleteFormat("key: >");
+  verifyIncompleteFormat(": value");
+  verifyIncompleteFormat(": {}");
+  verifyIncompleteFormat(": <>");
+  verifyIncompleteFormat(": []");
+  verifyIncompleteFormat("}\n"
+                         "key: value");
+  verifyIncompleteFormat("]\n"
+                         "key: value");
+  verifyIncompleteFormat("> key: value");
+  verifyIncompleteFormat("data { key: {");
+  verifyIncompleteFormat("data < key: [");
+  verifyIncompleteFormat("data [ key: {");
+  verifyIncompleteFormat("> key: value {");
+  verifyIncompleteFormat("> key: [");
+  verifyIncompleteFormat("}\n"
+                         "key: {");
+  verifyIncompleteFormat("data { key: 1 id:");
+  verifyIncompleteFormat("}\n"
+                         "key {");
+  verifyIncompleteFormat("> <");
+}
+
 } // end namespace tooling
 } // end namespace clang