[core] Declare apply locals right before their first use

A local declared at the top ran option_at before a publish placed before
the statement, which changed the call order and grew ld2412 by 16 bytes.

esphome/core/entity_helpers.py

@@ -477,7 +477,7 @@ ApplyPublish = Literal["before", "after"] | None
 class ApplyEntity:
     """A domain's ``Apply*`` class, its generated function's parameters and its publish statement.
 
-    ``locals`` are (name, declaration) pairs, emitted only when the body uses the name.
+    ``locals`` are (name, declaration) pairs, declared only when the body uses the name.
     """
 
     cls: MockObjClass
@@ -567,12 +567,11 @@ class SubEntities:
             body.insert(0, apply_entity.publish)
         elif publish == "after":
             body.append(apply_entity.publish)
-        text = "\n".join(body)
-        body[:0] = [
-            decl
-            for name, decl in apply_entity.locals
-            if re.search(rf"\b{name}\b", text)
-        ]
+        for name, decl in apply_entity.locals:
+            # Declared right before its first use, so calls keep their order.
+            uses = (i for i, line in enumerate(body) if re.search(rf"\b{name}\b", line))
+            if (first := next(uses, None)) is not None:
+                body.insert(first, decl)
         functions: dict[str, SafeExpType] = CORE.data.setdefault(_APPLY_DOMAIN, {})
         key = "\n".join([*(f"{t} {n}" for t, n in apply_entity.params), *body])
         if (fn := functions.get(key)) is None:

tests/unit_tests/core/test_entity_helpers.py

@@ -1396,17 +1396,28 @@ _SELECT_APPLY = entity_helpers.ApplyEntity(
 
 @pytest.mark.asyncio
 @pytest.mark.parametrize(
-    ("apply", "body"),
+    ("apply", "publish", "body"),
     [
         (
             "set_mode(option)",
+            "after",
             (
                 "const char *option = entity->option_at(index);\n"
                 "::hub->set_mode(option);\nentity->publish_state(index);"
             ),
         ),
+        (
+            "set_mode(option)",
+            "before",
+            (
+                "entity->publish_state(index);\n"
+                "const char *option = entity->option_at(index);\n"
+                "::hub->set_mode(option);"
+            ),
+        ),
         (
             "set_mode(index, options_)",
+            "after",
             "::hub->set_mode(index, options_);\nentity->publish_state(index);",
         ),
     ],
@@ -1415,12 +1426,13 @@ async def test_sub_entities_apply_locals(
     setup_test_environment: list[str],
     apply_functions: list[tuple[str, str, str]],
     apply: str,
+    publish: str,
     body: str,
 ) -> None:
-    """A local is declared only when the body names it as a whole identifier."""
+    """A local is declared before its first use, and only when named as a whole identifier."""
     conf = _apply_conf("m_sel", _SELECT_APPLY.cls)
     sub = _apply_sub([], {"m": conf}, _SELECT_APPLY)
-    await sub("m", None, apply=apply, publish="after")
+    await sub("m", None, apply=apply, publish=publish)
     assert apply_functions == [
         ("esphome__m_sel__fn", "select::Select * entity, size_t index", body)
     ]