[TableGen] [DetailedRecords] Print record name that is null string as ""

Differential Revision: https://reviews.llvm.org/D95312

Add a test for the backend.

lib/TableGen/DetailedRecordsBackend.cpp

@@ -104,7 +104,8 @@ void DetailedRecordsEmitter::printRecords(raw_ostream &OS) {
 
   for (const auto &RecPair : RecordList) {
     auto *const Rec = RecPair.second.get();
-    OS << formatv("\n{0}  |{1}|\n", Rec->getNameInitAsString(),
+    std::string Name = Rec->getNameInitAsString();
+    OS << formatv("\n{0}  |{1}|\n", Name.empty() ? "\"\"" : Name,
                   SrcMgr.getFormattedLocationNoOffset(Rec->getLoc().front()));
     printDefms(Rec, OS);
     printSuperclasses(Rec, OS);

test/TableGen/detailed-records.td

@@ -0,0 +1,36 @@
+// RUN: llvm-tblgen -print-detailed-records %s | FileCheck %s
+
+// This test file ensures that the DetailedRecords backend prints all
+// the global variables, classes, and records.
+
+// CHECK: ----- Global Variables
+// CHECK: Answer
+// CHECK: Greeting
+
+// CHECK: ----- Classes
+// CHECK: Class1
+// CHECK: Class2
+
+// CHECK: ----- Records
+// CHECK: ""
+// CHECK: Info
+// CHECK: Rec1
+// CHECK: anonymous_0
+
+defvar Greeting = "Hello there.";
+defvar Answer = 42;
+
+class Class1 {
+}
+
+class Class2 {
+}
+
+def : Class1;
+
+def "" : Class2;
+
+def Rec1;
+
+def Info : Class1;
+