xdrgen: Generate "if" instead of "switch" for boolean union enumerators

Eliminate this warning in code generated by xdrgen:

fs/nfsd/nfs3xdr_gen.c:220:2: warning: switch condition has boolean value [-Wswitch-bool]
  220 |         switch (ptr->attributes_follow) {
      |         ^       ~~~~~~~~~~~~~~~~~~~~~~

No more -Wswitch-bool warnings when compiling with W=1.

The generated code is functionally equivalent but somewhat more
idiomatic.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202511172336.Y75zj4v6-lkp@intel.com/
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

3 files changed, 109 insertions, 20 deletions

diff --git a/tools/net/sunrpc/xdrgen/generators/union.py b/tools/net/sunrpc/xdrgen/generators/union.py
index ad1f214ef22a..d15837dae651 100644
--- a/tools/net/sunrpc/xdrgen/generators/union.py
+++ b/tools/net/sunrpc/xdrgen/generators/union.py
@@ -84,6 +84,31 @@ def emit_union_switch_spec_decoder(
     print(template.render(name=node.name, type=node.spec.type_name))
 
 
+def emit_union_arm_decoder(
+    environment: Environment, node: _XdrCaseSpec
+) -> None:
+    """Emit decoder for an XDR union's arm (data only, no case/break)"""
+
+    if isinstance(node.arm, _XdrVoid):
+        return
+    if isinstance(node.arm, _XdrString):
+        type_name = "char *"
+        classifier = ""
+    else:
+        type_name = node.arm.spec.type_name
+        classifier = node.arm.spec.c_classifier
+
+    assert isinstance(node.arm, (_XdrBasic, _XdrString))
+    template = get_jinja2_template(environment, "decoder", node.arm.template)
+    print(
+        template.render(
+            name=node.arm.name,
+            type=type_name,
+            classifier=classifier,
+        )
+    )
+
+
 def emit_union_case_spec_decoder(
     environment: Environment, node: _XdrCaseSpec, big_endian_discriminant: bool
 ) -> None:
@@ -151,19 +176,33 @@ def emit_union_decoder(environment: Environment, node: _XdrUnion) -> None:
     template = get_jinja2_template(environment, "decoder", "open")
     print(template.render(name=node.name))
 
-    emit_union_switch_spec_decoder(environment, node.discriminant)
+    # For boolean discriminants, use if statement instead of switch
+    if node.discriminant.spec.type_name == "bool":
+        template = get_jinja2_template(environment, "decoder", "bool_spec")
+        print(template.render(name=node.discriminant.name, type=node.discriminant.spec.type_name))
 
-    for case in node.cases:
-        emit_union_case_spec_decoder(
-            environment,
-            case,
-            node.discriminant.spec.type_name in big_endian,
-        )
+        # Find and emit the TRUE case
+        for case in node.cases:
+            if case.values and case.values[0] == "TRUE":
+                emit_union_arm_decoder(environment, case)
+                break
 
-    emit_union_default_spec_decoder(environment, node)
+        template = get_jinja2_template(environment, "decoder", "close")
+        print(template.render())
+    else:
+        emit_union_switch_spec_decoder(environment, node.discriminant)
 
-    template = get_jinja2_template(environment, "decoder", "close")
-    print(template.render())
+        for case in node.cases:
+            emit_union_case_spec_decoder(
+                environment,
+                case,
+                node.discriminant.spec.type_name in big_endian,
+            )
+
+        emit_union_default_spec_decoder(environment, node)
+
+        template = get_jinja2_template(environment, "decoder", "close")
+        print(template.render())
 
 
 def emit_union_switch_spec_encoder(
@@ -175,6 +214,28 @@ def emit_union_switch_spec_encoder(
     print(template.render(name=node.name, type=node.spec.type_name))
 
 
+def emit_union_arm_encoder(
+    environment: Environment, node: _XdrCaseSpec
+) -> None:
+    """Emit encoder for an XDR union's arm (data only, no case/break)"""
+
+    if isinstance(node.arm, _XdrVoid):
+        return
+    if isinstance(node.arm, _XdrString):
+        type_name = "char *"
+    else:
+        type_name = node.arm.spec.type_name
+
+    assert isinstance(node.arm, (_XdrBasic, _XdrString))
+    template = get_jinja2_template(environment, "encoder", node.arm.template)
+    print(
+        template.render(
+            name=node.arm.name,
+            type=type_name,
+        )
+    )
+
+
 def emit_union_case_spec_encoder(
     environment: Environment, node: _XdrCaseSpec, big_endian_discriminant: bool
 ) -> None:
@@ -235,19 +296,33 @@ def emit_union_encoder(environment, node: _XdrUnion) -> None:
     template = get_jinja2_template(environment, "encoder", "open")
     print(template.render(name=node.name))
 
-    emit_union_switch_spec_encoder(environment, node.discriminant)
+    # For boolean discriminants, use if statement instead of switch
+    if node.discriminant.spec.type_name == "bool":
+        template = get_jinja2_template(environment, "encoder", "bool_spec")
+        print(template.render(name=node.discriminant.name, type=node.discriminant.spec.type_name))
 
-    for case in node.cases:
-        emit_union_case_spec_encoder(
-            environment,
-            case,
-            node.discriminant.spec.type_name in big_endian,
-        )
+        # Find and emit the TRUE case
+        for case in node.cases:
+            if case.values and case.values[0] == "TRUE":
+                emit_union_arm_encoder(environment, case)
+                break
 
-    emit_union_default_spec_encoder(environment, node)
+        template = get_jinja2_template(environment, "encoder", "close")
+        print(template.render())
+    else:
+        emit_union_switch_spec_encoder(environment, node.discriminant)
 
-    template = get_jinja2_template(environment, "encoder", "close")
-    print(template.render())
+        for case in node.cases:
+            emit_union_case_spec_encoder(
+                environment,
+                case,
+                node.discriminant.spec.type_name in big_endian,
+            )
+
+        emit_union_default_spec_encoder(environment, node)
+
+        template = get_jinja2_template(environment, "encoder", "close")
+        print(template.render())
 
 
 def emit_union_maxsize(environment: Environment, node: _XdrUnion) -> None:
diff --git a/tools/net/sunrpc/xdrgen/templates/C/union/decoder/bool_spec.j2 b/tools/net/sunrpc/xdrgen/templates/C/union/decoder/bool_spec.j2
new file mode 100644
index 000000000000..05ad491f74af
--- /dev/null
+++ b/tools/net/sunrpc/xdrgen/templates/C/union/decoder/bool_spec.j2
@@ -0,0 +1,7 @@
+{# SPDX-License-Identifier: GPL-2.0 #}
+{% if annotate %}
+	/* discriminant {{ name }} */
+{% endif %}
+	if (!xdrgen_decode_{{ type }}(xdr, &ptr->{{ name }}))
+		return false;
+	if (ptr->{{ name }}) {
diff --git a/tools/net/sunrpc/xdrgen/templates/C/union/encoder/bool_spec.j2 b/tools/net/sunrpc/xdrgen/templates/C/union/encoder/bool_spec.j2
new file mode 100644
index 000000000000..e5135ed6471c
--- /dev/null
+++ b/tools/net/sunrpc/xdrgen/templates/C/union/encoder/bool_spec.j2
@@ -0,0 +1,7 @@
+{# SPDX-License-Identifier: GPL-2.0 #}
+{% if annotate %}
+	/* discriminant {{ name }} */
+{% endif %}
+	if (!xdrgen_encode_{{ type }}(xdr, ptr->{{ name }}))
+		return false;
+	if (ptr->{{ name }}) {