[MLIR][Python] Add docstring for generated python op classes (#158198)

This PR adds support in mlir-tblgen for generating docstrings for each
Python class corresponding to an MLIR op. The docstrings are currently
derived from the op’s description in ODS, with indentation adjusted to
display nicely in Python. This makes it easier for Python users to see
the op descriptions directly in their IDE or LSP while coding.

In the future, we can extend the docstrings to include explanations for
each method, attribute, and so on.

This idea was previously discussed in the `#mlir-python` channel on
Discord with makslevental and superbobry.

---------

Co-authored-by: Maksim Levental <[email protected]>

Author: PragmaTwice

mlir/tools/mlir-tblgen/OpPythonBindingGen.cpp

@@ -13,13 +13,15 @@
 
 #include "OpGenHelpers.h"
 
+#include "mlir/Support/IndentedOstream.h"
 #include "mlir/TableGen/GenInfo.h"
 #include "mlir/TableGen/Operator.h"
 #include "llvm/ADT/StringSet.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/FormatVariadic.h"
 #include "llvm/TableGen/Error.h"
 #include "llvm/TableGen/Record.h"
+#include <regex>
 
 using namespace mlir;
 using namespace mlir::tblgen;
@@ -61,10 +63,11 @@ from ._{0}_ops_gen import _Dialect
 
 /// Template for operation class:
 ///   {0} is the Python class name;
-///   {1} is the operation name.
+///   {1} is the operation name;
+///   {2} is the docstring for this operation.
 constexpr const char *opClassTemplate = R"Py(
 @_ods_cext.register_operation(_Dialect)
-class {0}(_ods_ir.OpView):
+class {0}(_ods_ir.OpView):{2}
   OPERATION_NAME = "{1}"
 )Py";
 
@@ -1031,9 +1034,31 @@ static void emitValueBuilder(const Operator &op,
   }
 }
 
+/// Retrieve the description of the given op and generate a docstring for it.
+static std::string makeDocStringForOp(const Operator &op) {
+  if (!op.hasDescription())
+    return "";
+
+  auto desc = op.getDescription().rtrim(" \t").str();
+  // Replace all """ with \"\"\" to avoid early termination of the literal.
+  desc = std::regex_replace(desc, std::regex(R"(""")"), R"(\"\"\")");
+
+  std::string docString = "\n";
+  llvm::raw_string_ostream os(docString);
+  raw_indented_ostream identedOs(os);
+  os << R"(  r""")" << "\n";
+  identedOs.printReindented(desc, "  ");
+  if (!StringRef(desc).ends_with("\n"))
+    os << "\n";
+  os << R"(  """)" << "\n";
+
+  return docString;
+}
+
 /// Emits bindings for a specific Op to the given output stream.
 static void emitOpBindings(const Operator &op, raw_ostream &os) {
-  os << formatv(opClassTemplate, op.getCppClassName(), op.getOperationName());
+  os << formatv(opClassTemplate, op.getCppClassName(), op.getOperationName(),
+                makeDocStringForOp(op));
 
   // Sized segments.
   if (op.getTrait(attrSizedTraitForKind("operand")) != nullptr) {