[clang] [llvm] [Support] Add scaling support in `indent` (PR #109478)

[Matt Arsenault via cfe-commits]

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@@ -774,18 +774,27 @@ class buffer_unique_ostream : public raw_svector_ostream {
 // you can use
 // OS << indent(6) << "more stuff";
 // which has better ergonomics (and clang-formats better as well).
+//
+// If indentation is always in increments of a fixed value, you can use Scale
+// to set that value once. So indent(1, 2) will add 2 spaces and
+// indent(1,2) + 1 will add 4 spaces.
 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); }
+  // Indentation is represented as `NumIndents` steps of size `Scale` each.
+  unsigned NumIndents;
+  unsigned Scale;
+
+  explicit indent(unsigned NumIndents, unsigned Scale = 1)
+      : NumIndents(NumIndents), Scale(Scale) {}
+
+  // These arithmeric operators preserve scale.
+  void operator+=(unsigned N) { NumIndents += N; }
+  void operator-=(unsigned N) { NumIndents -= N; }
+  indent operator+(unsigned N) const { return indent(NumIndents + N, Scale); }
+  indent operator-(unsigned N) const { return indent(NumIndents - N, Scale); }
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arsenm wrote:

I'm surprised there's no guard against underflow here 

https://github.com/llvm/llvm-project/pull/109478