xdrgen: Implement pass-through lines in specifications

XDR specification files can contain lines prefixed with '%' that
pass through unchanged to generated output. Traditional rpcgen
removes the '%' and emits the remainder verbatim, allowing direct
insertion of C includes, pragma directives, or other language-
specific content into the generated code.

Until now, xdrgen silently discarded these lines during parsing.
This prevented specifications from including necessary headers or
preprocessor directives that might be required for the generated
code to compile correctly.

The grammar now captures pass-through lines instead of ignoring
them. A new AST node type represents pass-through content, and
the AST transformer strips the leading '%' character. Definition
and source generators emit pass-through content in document order,
preserving the original placement within the specification.

This brings xdrgen closer to feature parity with traditional
rpcgen while maintaining the existing document-order processing
model.

Existing generated xdrgen source code has been regenerated.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

9 files changed, 95 insertions, 17 deletions

diff --git a/tools/net/sunrpc/xdrgen/README b/tools/net/sunrpc/xdrgen/README
index 27218a78ab40..2cf05d1e4cd9 100644
--- a/tools/net/sunrpc/xdrgen/README
+++ b/tools/net/sunrpc/xdrgen/README
@@ -250,8 +250,6 @@ Add more pragma directives:
 Enable something like a #include to dynamically insert the content
 of other specification files
 
-Properly support line-by-line pass-through via the "%" decorator
-
 Build a unit test suite for verifying translation of XDR language
 into compilable code
 
diff --git a/tools/net/sunrpc/xdrgen/generators/passthru.py b/tools/net/sunrpc/xdrgen/generators/passthru.py
new file mode 100644
index 000000000000..cb17bd977f1e
--- /dev/null
+++ b/tools/net/sunrpc/xdrgen/generators/passthru.py
@@ -0,0 +1,26 @@
+#!/usr/bin/env python3
+# ex: set filetype=python:
+
+"""Generate code for XDR pass-through lines"""
+
+from generators import SourceGenerator, create_jinja2_environment
+from xdr_ast import _XdrPassthru
+
+
+class XdrPassthruGenerator(SourceGenerator):
+    """Generate source code for XDR pass-through content"""
+
+    def __init__(self, language: str, peer: str):
+        """Initialize an instance of this class"""
+        self.environment = create_jinja2_environment(language, "passthru")
+        self.peer = peer
+
+    def emit_definition(self, node: _XdrPassthru) -> None:
+        """Emit one pass-through line"""
+        template = self.environment.get_template("definition.j2")
+        print(template.render(content=node.content))
+
+    def emit_decoder(self, node: _XdrPassthru) -> None:
+        """Emit one pass-through line"""
+        template = self.environment.get_template("source.j2")
+        print(template.render(content=node.content))
diff --git a/tools/net/sunrpc/xdrgen/grammars/xdr.lark b/tools/net/sunrpc/xdrgen/grammars/xdr.lark
index b7c664f2acb7..1d2afff98ac5 100644
--- a/tools/net/sunrpc/xdrgen/grammars/xdr.lark
+++ b/tools/net/sunrpc/xdrgen/grammars/xdr.lark
@@ -78,6 +78,9 @@ definition              : constant_def
                         | type_def
                         | program_def
                         | pragma_def
+                        | passthru_def
+
+passthru_def            : PASSTHRU
 
 //
 // RPC program definitions not specified in RFC 4506
@@ -115,8 +118,7 @@ decimal_constant        : /[\+-]?(0|[1-9][0-9]*)/
 hexadecimal_constant    : /0x([a-f]|[A-F]|[0-9])+/
 octal_constant          : /0[0-7]+/
 
-PASSTHRU                : "%" | "%" /.+/
-%ignore PASSTHRU
+PASSTHRU                : /%.*/
 
 %import common.C_COMMENT
 %ignore C_COMMENT
diff --git a/tools/net/sunrpc/xdrgen/subcmds/declarations.py b/tools/net/sunrpc/xdrgen/subcmds/declarations.py
index 97ffb76a02f1..ed83d48d1f68 100644
--- a/tools/net/sunrpc/xdrgen/subcmds/declarations.py
+++ b/tools/net/sunrpc/xdrgen/subcmds/declarations.py
@@ -10,7 +10,6 @@ from argparse import Namespace
 from lark import logger
 from lark.exceptions import VisitError
 
-from generators.constant import XdrConstantGenerator
 from generators.enum import XdrEnumGenerator
 from generators.header_bottom import XdrHeaderBottomGenerator
 from generators.header_top import XdrHeaderTopGenerator
@@ -21,8 +20,7 @@ from generators.struct import XdrStructGenerator
 from generators.union import XdrUnionGenerator
 
 from xdr_ast import transform_parse_tree, _RpcProgram, Specification
-from xdr_ast import _XdrConstant, _XdrEnum, _XdrPointer
-from xdr_ast import _XdrTypedef, _XdrStruct, _XdrUnion
+from xdr_ast import _XdrEnum, _XdrPointer, _XdrTypedef, _XdrStruct, _XdrUnion
 from xdr_parse import xdr_parser, set_xdr_annotate
 from xdr_parse import make_error_handler, XdrParseError
 from xdr_parse import handle_transform_error
diff --git a/tools/net/sunrpc/xdrgen/subcmds/definitions.py b/tools/net/sunrpc/xdrgen/subcmds/definitions.py
index b17526a03dda..a48ca0549382 100644
--- a/tools/net/sunrpc/xdrgen/subcmds/definitions.py
+++ b/tools/net/sunrpc/xdrgen/subcmds/definitions.py
@@ -14,6 +14,7 @@ from generators.constant import XdrConstantGenerator
 from generators.enum import XdrEnumGenerator
 from generators.header_bottom import XdrHeaderBottomGenerator
 from generators.header_top import XdrHeaderTopGenerator
+from generators.passthru import XdrPassthruGenerator
 from generators.pointer import XdrPointerGenerator
 from generators.program import XdrProgramGenerator
 from generators.typedef import XdrTypedefGenerator
@@ -21,7 +22,7 @@ from generators.struct import XdrStructGenerator
 from generators.union import XdrUnionGenerator
 
 from xdr_ast import transform_parse_tree, Specification
-from xdr_ast import _RpcProgram, _XdrConstant, _XdrEnum, _XdrPointer
+from xdr_ast import _RpcProgram, _XdrConstant, _XdrEnum, _XdrPassthru, _XdrPointer
 from xdr_ast import _XdrTypedef, _XdrStruct, _XdrUnion
 from xdr_parse import xdr_parser, set_xdr_annotate
 from xdr_parse import make_error_handler, XdrParseError
@@ -47,6 +48,8 @@ def emit_header_definitions(root: Specification, language: str, peer: str) -> No
             gen = XdrStructGenerator(language, peer)
         elif isinstance(definition.value, _XdrUnion):
             gen = XdrUnionGenerator(language, peer)
+        elif isinstance(definition.value, _XdrPassthru):
+            gen = XdrPassthruGenerator(language, peer)
         else:
             continue
         gen.emit_definition(definition.value)
diff --git a/tools/net/sunrpc/xdrgen/subcmds/source.py b/tools/net/sunrpc/xdrgen/subcmds/source.py
index 6508563494fe..27e8767b1b58 100644
--- a/tools/net/sunrpc/xdrgen/subcmds/source.py
+++ b/tools/net/sunrpc/xdrgen/subcmds/source.py
@@ -12,6 +12,7 @@ from lark.exceptions import VisitError
 
 from generators.source_top import XdrSourceTopGenerator
 from generators.enum import XdrEnumGenerator
+from generators.passthru import XdrPassthruGenerator
 from generators.pointer import XdrPointerGenerator
 from generators.program import XdrProgramGenerator
 from generators.typedef import XdrTypedefGenerator
@@ -19,7 +20,7 @@ from generators.struct import XdrStructGenerator
 from generators.union import XdrUnionGenerator
 
 from xdr_ast import transform_parse_tree, _RpcProgram, Specification
-from xdr_ast import _XdrAst, _XdrEnum, _XdrPointer
+from xdr_ast import _XdrAst, _XdrEnum, _XdrPassthru, _XdrPointer
 from xdr_ast import _XdrStruct, _XdrTypedef, _XdrUnion
 
 from xdr_parse import xdr_parser, set_xdr_annotate, set_xdr_enum_validation
@@ -74,22 +75,31 @@ def generate_server_source(filename: str, root: Specification, language: str) ->
     gen.emit_source(filename, root)
 
     for definition in root.definitions:
-        emit_source_decoder(definition.value, language, "server")
+        if isinstance(definition.value, _XdrPassthru):
+            passthru_gen = XdrPassthruGenerator(language, "server")
+            passthru_gen.emit_decoder(definition.value)
+        else:
+            emit_source_decoder(definition.value, language, "server")
     for definition in root.definitions:
-        emit_source_encoder(definition.value, language, "server")
+        if not isinstance(definition.value, _XdrPassthru):
+            emit_source_encoder(definition.value, language, "server")
 
 
 def generate_client_source(filename: str, root: Specification, language: str) -> None:
-    """Generate server-side source code"""
+    """Generate client-side source code"""
 
     gen = XdrSourceTopGenerator(language, "client")
     gen.emit_source(filename, root)
 
-    print("")
     for definition in root.definitions:
-        emit_source_encoder(definition.value, language, "client")
+        if isinstance(definition.value, _XdrPassthru):
+            passthru_gen = XdrPassthruGenerator(language, "client")
+            passthru_gen.emit_decoder(definition.value)
+        else:
+            emit_source_encoder(definition.value, language, "client")
     for definition in root.definitions:
-        emit_source_decoder(definition.value, language, "client")
+        if not isinstance(definition.value, _XdrPassthru):
+            emit_source_decoder(definition.value, language, "client")
 
     # cel: todo: client needs PROC macros
 
diff --git a/tools/net/sunrpc/xdrgen/templates/C/passthru/definition.j2 b/tools/net/sunrpc/xdrgen/templates/C/passthru/definition.j2
new file mode 100644
index 000000000000..900c7516a29c
--- /dev/null
+++ b/tools/net/sunrpc/xdrgen/templates/C/passthru/definition.j2
@@ -0,0 +1,3 @@
+{# SPDX-License-Identifier: GPL-2.0 #}
+
+{{ content }}
diff --git a/tools/net/sunrpc/xdrgen/templates/C/passthru/source.j2 b/tools/net/sunrpc/xdrgen/templates/C/passthru/source.j2
new file mode 100644
index 000000000000..900c7516a29c
--- /dev/null
+++ b/tools/net/sunrpc/xdrgen/templates/C/passthru/source.j2
@@ -0,0 +1,3 @@
+{# SPDX-License-Identifier: GPL-2.0 #}
+
+{{ content }}
diff --git a/tools/net/sunrpc/xdrgen/xdr_ast.py b/tools/net/sunrpc/xdrgen/xdr_ast.py
index dc2fa9fd8ec2..14bff9477473 100644
--- a/tools/net/sunrpc/xdrgen/xdr_ast.py
+++ b/tools/net/sunrpc/xdrgen/xdr_ast.py
@@ -517,6 +517,13 @@ class _Pragma(_XdrAst):
 
 
 @dataclass
+class _XdrPassthru(_XdrAst):
+    """Passthrough line to emit verbatim in output"""
+
+    content: str
+
+
+@dataclass
 class Definition(_XdrAst, ast_utils.WithMeta):
     """Corresponds to 'definition' in the grammar"""
 
@@ -738,14 +745,42 @@ class ParseToAst(Transformer):
                 raise NotImplementedError("Directive not supported")
         return _Pragma()
 
+    def passthru_def(self, children):
+        """Instantiate one _XdrPassthru object"""
+        token = children[0]
+        content = token.value[1:]
+        return _XdrPassthru(content)
+
 
 transformer = ast_utils.create_transformer(this_module, ParseToAst())
 
 
+def _merge_consecutive_passthru(definitions: List[Definition]) -> List[Definition]:
+    """Merge consecutive passthru definitions into single nodes"""
+    result = []
+    i = 0
+    while i < len(definitions):
+        if isinstance(definitions[i].value, _XdrPassthru):
+            lines = [definitions[i].value.content]
+            meta = definitions[i].meta
+            j = i + 1
+            while j < len(definitions) and isinstance(definitions[j].value, _XdrPassthru):
+                lines.append(definitions[j].value.content)
+                j += 1
+            merged = _XdrPassthru("\n".join(lines))
+            result.append(Definition(meta, merged))
+            i = j
+        else:
+            result.append(definitions[i])
+            i += 1
+    return result
+
+
 def transform_parse_tree(parse_tree):
     """Transform productions into an abstract syntax tree"""
-
-    return transformer.transform(parse_tree)
+    ast = transformer.transform(parse_tree)
+    ast.definitions = _merge_consecutive_passthru(ast.definitions)
+    return ast
 
 
 def get_header_name() -> str: