[Support] Add helper struct indent for adding indentation (#108966)

Add helper struct indent() for adding indentation to raw_ostream.

llvm/include/llvm/Support/raw_ostream.h

@@ -769,6 +769,25 @@ public:
   ~buffer_unique_ostream() override { *OS << str(); }
 };
 
+// Helper struct to add indentation to raw_ostream. Instead of
+// OS.indent(6) << "more stuff";
+// you can use
+// OS << indent(6) << "more stuff";
+// which has better ergonomics (and clang-formats better as well).
+struct indent {
+  unsigned NumSpaces;
+
+  explicit indent(unsigned NumSpaces) : NumSpaces(NumSpaces) {}
+  void operator+=(unsigned N) { NumSpaces += N; }
+  void operator-=(unsigned N) { NumSpaces -= N; }
+  indent operator+(unsigned N) const { return indent(NumSpaces + N); }
+  indent operator-(unsigned N) const { return indent(NumSpaces - N); }
+};
+
+inline raw_ostream &operator<<(raw_ostream &OS, const indent &Indent) {
+  return OS.indent(Indent.NumSpaces);
+}
+
 class Error;
 
 /// This helper creates an output stream and then passes it to \p Write.

llvm/unittests/Support/raw_ostream_test.cpp

@@ -177,6 +177,19 @@ TEST(raw_ostreamTest, Justify) {
   EXPECT_EQ("none",    printToString(center_justify("none", 1), 1));
 }
 
+TEST(raw_ostreamTest, Indent) {
+  indent Indent(4);
+  auto Spaces = [](int N) { return std::string(N, ' '); };
+  EXPECT_EQ(Spaces(4), printToString(Indent));
+  EXPECT_EQ("", printToString(indent(0)));
+  EXPECT_EQ(Spaces(5), printToString(Indent + 1));
+  EXPECT_EQ(Spaces(3), printToString(Indent - 1));
+  Indent += 1;
+  EXPECT_EQ(Spaces(5), printToString(Indent));
+  Indent -= 1;
+  EXPECT_EQ(Spaces(4), printToString(Indent));
+}
+
 TEST(raw_ostreamTest, FormatHex) {  
   EXPECT_EQ("0x1234",     printToString(format_hex(0x1234, 6), 6));
   EXPECT_EQ("0x001234",   printToString(format_hex(0x1234, 8), 8));

llvm/utils/yaml-bench/YAMLBench.cpp

@@ -56,17 +56,6 @@ cl::opt<cl::boolOrDefault>
     UseColor("use-color", cl::desc("Emit colored output (default=autodetect)"),
              cl::init(cl::BOU_UNSET));
 
-struct indent {
-  unsigned distance;
-  indent(unsigned d) : distance(d) {}
-};
-
-static raw_ostream &operator <<(raw_ostream &os, const indent &in) {
-  for (unsigned i = 0; i < in.distance; ++i)
-    os << "  ";
-  return os;
-}
-
 /// Pretty print a tag by replacing tag:yaml.org,2002: with !!.
 static std::string prettyTag(yaml::Node *N) {
   std::string Tag = N->getVerbatimTag();