[api] Key the generated decode switch on the wire tag on every target

The host no longer gets its own switch shape through USE_HOST; every build compiles the
same switch on the field's wire tag.

esphome/components/api/proto.h

@@ -170,20 +170,9 @@ class ProtoVarInt {
 class ProtoMessage;
 class ProtoSize;
 
-// Switch key for generated decode_field() bodies. Embedded builds use compare chains
-// (-fno-jump-tables), so the full tag is one compare per field with no guard. The host gets a
-// jump table from the dense field number switch plus a tag compare that rejects the wrong wire type.
-#ifdef USE_HOST
-#define PROTO_DECODE_KEY(tag) ((tag) >> 3)
-#define PROTO_DECODE_CASE(field_id, wire_type) (field_id)
-#define PROTO_DECODE_GUARD(tag, field_id, wire_type) \
-  if ((tag) != (((field_id) << 3) | (wire_type))) \
-  return false
-#else
-#define PROTO_DECODE_KEY(tag) (tag)
-#define PROTO_DECODE_CASE(field_id, wire_type) (((field_id) << 3) | (wire_type))
-#define PROTO_DECODE_GUARD(tag, field_id, wire_type) (void) 0
-#endif
+/// Case label for decode_field(): the wire tag of a field, so a field that arrives with another wire
+/// type matches no case.
+constexpr uint32_t proto_tag(uint32_t field_id, uint32_t wire_type) { return (field_id << 3) | wire_type; }
 
 /// One decoded field: the payload pointer and a scalar holding the varint or fixed32 value, or the
 /// length of a length-delimited field. The wire type in the tag says which applies; accessors do not check.

script/api_protobuf/api_protobuf.py

@@ -28,6 +28,11 @@ class WireType(IntEnum):
     END_GROUP = 4  # groups (deprecated)
     FIXED32 = 5  # fixed32, sfixed32, float
 
+    @property
+    def cpp_name(self) -> str:
+        """The matching constant in proto.h."""
+        return f"WIRE_TYPE_{self.name}"
+
 
 # Generate with
 # protoc --python_out=script/api_protobuf -I esphome/components/api/ api_options.proto
@@ -230,10 +235,9 @@ class TypeInfo(ABC):
         return f"{self.cpp_type} {self.field_name}{{{self.default_value}}};"
 
     def decode_case(self, body: str) -> str:
-        """Emit one decode_field() case, keyed through the PROTO_DECODE_* macros in proto.h."""
-        wire_type = int(self.wire_type)
-        return f"case PROTO_DECODE_CASE({self.number}, {wire_type}):\n" + indent(
-            f"PROTO_DECODE_GUARD(tag, {self.number}, {wire_type});\n{body}\nbreak;"
+        """Emit one decode_field() case, keyed on the field's wire tag."""
+        return f"case proto_tag({self.number}, {self.wire_type.cpp_name}):\n" + indent(
+            f"{body}\nbreak;"
         )
 
     # Decode expression per wire type; a decodable type sets exactly one.
@@ -2685,7 +2689,7 @@ def build_message_type(
     if decode:
         o = f"bool {desc.name}::decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) {{\n"
         o += "  const ProtoFieldValue value(data, scalar);\n"
-        o += "  switch (PROTO_DECODE_KEY(tag)) {\n"
+        o += "  switch (tag) {\n"
         o += indent("\n".join(decode), "    ") + "\n"
         o += "    default: return false;\n"
         o += "  }\n"

tests/unit_tests/components/api/test_api_protobuf_generator.py

@@ -197,22 +197,22 @@ def _decode_case(field_type: int, number: int) -> str:
 @pytest.mark.parametrize(
     ("field_type", "number", "wire_type", "accessor"),
     [
-        (UINT32, 2, 0, "value.as_varint()"),
-        (BOOL, 3, 0, "value.as_varint() != 0"),
-        (STRING, 1, 2, "value.data()"),
-        (FLOAT, 4, 5, "value.as_float()"),
-        (FIXED32, 5, 5, "value.as_fixed32()"),
+        (UINT32, 2, "WIRE_TYPE_VARINT", "value.as_varint()"),
+        (BOOL, 3, "WIRE_TYPE_VARINT", "value.as_varint() != 0"),
+        (STRING, 1, "WIRE_TYPE_LENGTH_DELIMITED", "value.data()"),
+        (FLOAT, 4, "WIRE_TYPE_FIXED32", "value.as_float()"),
+        (FIXED32, 5, "WIRE_TYPE_FIXED32", "value.as_fixed32()"),
     ],
 )
 def test_decode_cases_carry_field_number_and_wire_type(
-    field_type: int, number: int, wire_type: int, accessor: str
+    field_type: int, number: int, wire_type: str, accessor: str
 ) -> None:
     """Each decoded field yields one case keyed on its number and declared wire type."""
     case = _decode_case(field_type, number)
     lines = case.splitlines()
-    assert lines[0] == f"case PROTO_DECODE_CASE({number}, {wire_type}):", case
-    assert lines[1].strip() == f"PROTO_DECODE_GUARD(tag, {number}, {wire_type});", case
-    assert accessor in case, case
+    assert lines[0] == f"case proto_tag({number}, {wire_type}):", case
+    assert accessor in lines[1], case
+    assert lines[-1].strip() == "break;", case
 
 
 def test_message_gets_a_single_decode_field_override() -> None:
@@ -231,7 +231,11 @@ def test_message_gets_a_single_decode_field_override() -> None:
         )
         == 1
     )
-    assert "switch (PROTO_DECODE_KEY(tag)) {" in cpp
+    assert "switch (tag) {" in cpp
     assert "const ProtoFieldValue value(data, scalar);" in cpp
-    for number, wire_type in ((1, 2), (2, 0), (3, 5)):
-        assert f"case PROTO_DECODE_CASE({number}, {wire_type}):" in cpp, cpp
+    for number, wire_type in (
+        (1, "WIRE_TYPE_LENGTH_DELIMITED"),
+        (2, "WIRE_TYPE_VARINT"),
+        (3, "WIRE_TYPE_FIXED32"),
+    ):
+        assert f"case proto_tag({number}, {wire_type}):" in cpp, cpp