[mlir] Fix missing OpInterface docs newline

Fix incorrect markdown generated by mlir-tblgen for an InterfaceMethod
that includes a body.  Previously, this would cause the next method to
show up on the same line and produce incorrect markdown.  Newlines would
only be added if the method did _not_ provide a body.  E.g., previously
this was generating markdown like:

    some function comment#### `next method`

This change makes this generate as:

    some function comment

    #### `next method`

Signed-off-by: Schuyler Eldridge <[email protected]>

Reviewed By: rriddle

Differential Revision: https://reviews.llvm.org/D140590

Author: seldridge

mlir/test/mlir-tblgen/op-interface.td

@@ -1,5 +1,6 @@
 // RUN: mlir-tblgen -gen-op-interface-decls -I %S/../../include %s | FileCheck %s --check-prefix=DECL
 // RUN: mlir-tblgen -gen-op-decls -I %S/../../include %s | FileCheck %s --check-prefix=OP_DECL
+// RUN: mlir-tblgen -gen-op-interface-docs -I %S/../../include %s | FileCheck %s --check-prefix=DOCS
 
 include "mlir/IR/OpBase.td"
 
@@ -31,6 +32,13 @@ def TestOpInterface : OpInterface<"TestOpInterface"> {
       /*methodName=*/"foo",
       /*args=*/(ins "int":$input)
     >,
+    InterfaceMethod<
+      /*desc=*/[{some function comment}],
+      /*retTy=*/"int",
+      /*methodName=*/"body_foo",
+      /*args=*/(ins "int":$input),
+      /*body=*/[{ return 0; }]
+    >,
     InterfaceMethod<
       /*desc=*/[{some function comment}],
       /*retTy=*/"int",
@@ -93,3 +101,17 @@ def DeclareMethodsWithDefaultOp : Op<TestDialect, "declare_methods_op",
 // OP_DECL-LABEL: class DeclareMethodsWithDefaultOp : public
 // OP_DECL: int foo(int input);
 // OP_DECL: int default_foo(int input);
+
+// DOCS-LABEL: {{^}}## TestOpInterface (`TestOpInterface`)
+// DOCS: some op interface description
+
+// DOCS: {{^}}### Methods:
+
+// DOCS: {{^}}#### `foo`
+// DOCS: some function comment
+
+// DOCS: {{^}}#### `body_foo`
+// DOCS: some function comment
+
+// DOCS: {{^}}#### `default_foo`
+// DOCS: some function comment

mlir/tools/mlir-tblgen/OpInterfacesGen.cpp

@@ -557,7 +557,9 @@ static void emitInterfaceDoc(const llvm::Record &interfaceDef,
 
     // If the body is not provided, this method must be provided by the user.
     if (!method.getBody())
-      os << "\nNOTE: This method *must* be implemented by the user.\n\n";
+      os << "\nNOTE: This method *must* be implemented by the user.";
+
+    os << "\n\n";
   }
 }