Index: lib/Format/ContinuationIndenter.cpp
===================================================================
--- lib/Format/ContinuationIndenter.cpp
+++ lib/Format/ContinuationIndenter.cpp
@@ -745,7 +745,11 @@
       !Current.isOneOf(tok::colon, tok::comment))
     return ContinuationIndent;
   if (State.Stack.back().Indent == State.FirstIndent && PreviousNonComment &&
-      PreviousNonComment->isNot(tok::r_brace))
+      PreviousNonComment->isNot(tok::r_brace) &&
+      // Don't indent the second and next in a sequence of string literals.
+      // Such sequence might have been introduced by string literal breaking,
+      // so this is important to preserve idempotency.
+      !(PreviousNonComment->isStringLiteral() && Current.isStringLiteral()))
     // Ensure that we fall back to the continuation indent width instead of
     // just flushing continuations left.
     return State.Stack.back().Indent + Style.ContinuationIndentWidth;
Index: unittests/Format/FormatTest.cpp
===================================================================
--- unittests/Format/FormatTest.cpp
+++ unittests/Format/FormatTest.cpp
@@ -6748,6 +6748,22 @@
             format("\"test\\000000000001\"", getLLVMStyleWithColumns(10)));
 }
 
+TEST_F(FormatTest, KeepsIndentInASequenceOfStringLiteralsTheSame) {
+  verifyFormat("\"line 1\"\n"
+               "\"line 2\"");
+  verifyFormat("f(\"line 1\"\n"
+               "  \"line 2\");");
+  verifyFormat("{\n"
+               "  std::string a = \"line 1\"\n"
+               "                  \"line 2\"\n"
+               "                  \"line 3\";\n"
+               "}");
+  verifyFormat("auto a = \"line 1\"\n"
+               "         u\"line 2\";");
+  verifyFormat("@\"line 1\"\n"
+               "@\"line 2\";");
+}
+
 TEST_F(FormatTest, DoNotCreateUnreasonableUnwrappedLines) {
   verifyFormat("void f() {\n"
                "  return g() {}\n"
@@ -10098,7 +10114,6 @@
   EXPECT_TRUE(static_cast<bool>(Result));
   EXPECT_EQ(Expected, *Result);
 }
-
 } // end namespace
 } // end namespace format
 } // end namespace clang