scanner: drop the Target class, push to templates

The Target was specific to libei/libeis, it resolved to "ei" or
"eis_client" depending on which component we were building. But that's
specific to our C implementation here, so let's push it into our C
implementation templates.

proto/ei-proto.c.tmpl

@@ -7,9 +7,6 @@
 {#- this is a jinja template, warning above is for the generated file
 
    Non-obvious variables set by the scanner that are used in this template:
-   - target: because eis is actually eis_client in the code, the target points to
-     either "ei" or "eis_client". The various attributes on target resolve
-     accordingly.
    - request.fqdn/event.fqdn - the full name of a request/event with the
      interface name prefixed, "ei_foo_request_bar" or "ei_foo_event_bar"
    - incoming/outgoing: points to the list of requests or events, depending
@@ -17,6 +14,16 @@
      generating (ei or eis)
 #}
 
+{# target: because eis is actually eis_client in the code, the target points to
+   either "ei" or "eis_client" and we need the matching get_context or
+   get_client for those. This is specific to the libei/libeis implementation
+   so it's done here in the template only. #}
+{% set target = {} %}
+{% if component == "eis" %}
+{% set target = { "name":  "eis_client", "context": "client" }  %}
+{% else %}
+{% set target = { "name":  "ei", "context": "context" }  %}
+{% endif %}
 
 #include <assert.h>
 #include <errno.h>
@@ -39,7 +46,7 @@ struct {{target.name}};
  * message sending functions (requests for libei, events for libeis).
  */
 extern int {{target.name}}_send_message(
-  {{target.as_arg}}, const struct brei_object *obj, uint32_t opcode,
+  {{target.name|as_arg}}, const struct brei_object *obj, uint32_t opcode,
   const char *signature, size_t nargs, ...
 );
 
@@ -52,7 +59,7 @@ extern int {{target.name}}_send_message(
 const struct {{interface.name}}_interface *{{interface.name}}_get_interface({{interface.as_arg}});
 
 /* returns the message sending context from the given struct */
-{{target.ctype}} {{interface.name}}_get_{{target.context}}({{interface.as_arg}});
+{{target.name|ctype}} {{interface.name}}_get_{{target.context}}({{interface.as_arg}});
 
 /* Returns the protocol object id from the given struct */
 const struct brei_object *
@@ -77,7 +84,7 @@ int
 		return -ENOENT;
 
 	const struct brei_object *obj = {{interface.name}}_get_proto_object({{interface.name}});
-	{{target.ctype}} ctx = {{interface.name}}_get_{{target.context}}({{interface.name}});
+	{{target.name|ctype}} ctx = {{interface.name}}_get_{{target.context}}({{interface.name}});
 
 	if (obj->version < {{outgoing.fqdn.upper()}}_SINCE_VERSION)
 		return -ENOTSUP;

proto/ei-proto.h.tmpl

@@ -7,8 +7,6 @@
 {# this is a jinja template, warning above is for the generated file
 
    Non-obvious variables set by the scanner that are used in this template:
-   - target: because eis is actually eis_client in the code, the target points to
-     either "ei" or "eis_client"
    - request.fqdn/event.fqdn - the full name of a request/event with the
      interface name prefixed, "ei_foo_request_bar" or "ei_foo_event_bar"
    - incoming/outgoing: points to the list of requests or events, depending
@@ -16,6 +14,16 @@
      generating (ei or eis)
 #}
 
+{# target: because eis is actually eis_client in the code, the target points to
+   either "ei" or "eis_client" and we need the matching get_context or
+   get_client for those. This is specific to the libei/libeis implementation
+   so it's done here in the template only. #}
+{% if component == "eis" %}
+{% set target = { "name":  "eis_client", "context": "client" }  %}
+{% else %}
+{% set target = { "name":  "ei", "context": "context" }  %}
+{% endif %}
+
 #pragma once
 
 #ifdef _cplusplus

proto/scanner.py

@@ -36,35 +36,6 @@ def proto_to_type(proto: str) -> Optional[str]:
     }.get(proto)
 
 
-@attr.s
-class Target:
-    """
-    Defines the target struct for the base "ei" interface.
-
-    In libei we have a `struct ei` but in libeis the equivalent
-    level is `struct eis_client`. This target type maps those two.
-    """
-
-    name: str = attr.ib()
-    context: str = attr.ib()
-
-    @property
-    def ctype(self) -> str:
-        return f"struct {self.name} *"
-
-    @property
-    def as_param(self) -> str:
-        return f"struct {self.name}* {self.name}"
-
-    @property
-    def as_arg(self) -> str:
-        return self.as_param
-
-    @classmethod
-    def create(cls, name: str, context: str) -> "Target":
-        return cls(name=name, context=context)
-
-
 @attr.s
 class Argument:
     """
@@ -599,14 +570,9 @@ def generate_source(
     proto: Protocol, headerfile: Optional[str], template: Path, component: str
 ) -> jinja2.environment.TemplateStream:
     assert component in ["ei", "eis"]
-    target = {
-        "ei": Target.create("ei", context="context"),
-        "eis": Target.create("eis_client", context="client"),
-    }[component]
 
     data = {}
     data["component"] = component
-    data["target"] = target
     data["interfaces"] = proto.interfaces
     if headerfile:
         data["headerfile"] = headerfile
@@ -616,6 +582,17 @@ def generate_source(
         trim_blocks=True,
         lstrip_blocks=True,
     )
+
+    # jinja filter to convert foo into "struct foo *"
+    def filter_ctype(name):
+        return f"struct {name} *"
+
+    # jinja filter to convert foo into "struct foo *foo"
+    def filter_as_arg(name):
+        return f"struct {name} * {name}"
+
+    env.filters["ctype"] = filter_ctype
+    env.filters["as_arg"] = filter_as_arg
     jtemplate = env.get_template(template.name)
     return jtemplate.stream(data)