[mlir][ods] Skip adding TOC in doc gen when present

Enables adding a TOC in the description to be able to interleave
documentation before and after the TOC.

mlir/test/mlir-tblgen/gen-dialect-doc.td

@@ -0,0 +1,37 @@
+// RUN: mlir-tblgen -gen-dialect-doc -I %S/../../include %s | FileCheck %s
+
+include "mlir/IR/OpBase.td"
+
+def Test_Dialect : Dialect {
+  let name = "test";
+  let summary = "Dialect of ops to test";
+  let description = [{
+    Dialect without a [TOC] here.
+    TOC added by tool.
+  }];
+  let cppNamespace = "NS";
+}
+def AOp : Op<Test_Dialect, "a", []>;
+
+// CHECK: Dialect without a [TOC] here.
+// CHECK: TOC added by tool.
+// CHECK: [TOC]
+// CHECK-NOT: [TOC]
+
+def Toc_Dialect : Dialect {
+  let name = "test_toc";
+  let summary = "Dialect of ops to test";
+  let description = [{
+    Dialect with
+
+    [TOC]
+
+    here.
+  }];
+  let cppNamespace = "NS";
+}
+def BOp : Op<Toc_Dialect, "b", []>;
+
+// CHECK: Dialect with
+// CHECK: [TOC]
+// CHECK: here.

mlir/tools/mlir-tblgen/OpDocGen.cpp

@@ -21,6 +21,7 @@
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/FormatVariadic.h"
+#include "llvm/Support/Regex.h"
 #include "llvm/Support/Signals.h"
 #include "llvm/TableGen/Error.h"
 #include "llvm/TableGen/Record.h"
@@ -247,7 +248,10 @@ static void emitDialectDoc(const Dialect &dialect, ArrayRef<AttrDef> attrDefs,
   emitIfNotEmpty(dialect.getSummary(), os);
   emitIfNotEmpty(dialect.getDescription(), os);
 
-  os << "[TOC]\n\n";
+  // Generate a TOC marker except if description already contains one.
+  llvm::Regex r("^[[:space:]]*\\[TOC\\]$", llvm::Regex::RegexFlags::Newline);
+  if (!r.match(dialect.getDescription()))
+    os << "[TOC]\n\n";
 
   if (!attrDefs.empty()) {
     os << "## Attribute definition\n\n";