[PATCH 1/6] qapi: Add interfaces for alias support to Visitor

[Kevin Wolf <kwolf@redhat.com>]

This adds functions to the Visitor interface that can be used to define
aliases and alias scopes.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 include/qapi/visitor-impl.h | 12 ++++++++++++
 include/qapi/visitor.h      | 37 +++++++++++++++++++++++++++++++++++++
 qapi/qapi-visit-core.c      | 21 +++++++++++++++++++++
 3 files changed, 70 insertions(+)

diff --git a/include/qapi/visitor-impl.h b/include/qapi/visitor-impl.h
index 7362c043be..e30da2599c 100644
--- a/include/qapi/visitor-impl.h
+++ b/include/qapi/visitor-impl.h
@@ -113,6 +113,18 @@ struct Visitor
        The core takes care of the return type in the public interface. */
     void (*optional)(Visitor *v, const char *name, bool *present);
 
+    /*
+     * Optional; intended for input visitors. If not given, aliases are
+     * ignored.
+     */
+    void (*define_alias)(Visitor *v, const char *alias, const char **source);
+
+    /* Must be set if define_alias is set */
+    void (*start_alias_scope)(Visitor *v);
+
+    /* Must be set if define_alias is set */
+    void (*end_alias_scope)(Visitor *v);
+
     /* Must be set */
     VisitorType type;
 
diff --git a/include/qapi/visitor.h b/include/qapi/visitor.h
index ebc19ede7f..9bdc0ee03d 100644
--- a/include/qapi/visitor.h
+++ b/include/qapi/visitor.h
@@ -459,6 +459,43 @@ void visit_end_alternate(Visitor *v, void **obj);
  */
 bool visit_optional(Visitor *v, const char *name, bool *present);
 
+/*
+ * Defines a new alias rule.
+ *
+ * If @alias is non-NULL, the member named @alias in the external
+ * representation of the current struct is defined as an alias for the
+ * member described by @source.
+ *
+ * If @alias is NULL, all members of the struct described by @source are
+ * considered to have alias members with the same key in the current
+ * struct.
+ *
+ * @source is a NULL-terminated array of names that describe the path to
+ * a member, starting from the currently visited struct.
+ *
+ * The alias stays valid until the current alias scope ends.
+ * visit_start/end_struct() implicitly start/end an alias scope.
+ * Additionally, visit_start/end_alias_scope() can be used to explicitly
+ * create a nested alias scope.
+ */
+void visit_define_alias(Visitor *v, const char *alias, const char **source);
+
+/*
+ * Begins an explicit alias scope.
+ *
+ * Alias definitions after here will only stay valid until the
+ * corresponding visit_end_alias_scope() is called.
+ */
+void visit_start_alias_scope(Visitor *v);
+
+/*
+ * Ends an explicit alias scope.
+ *
+ * Alias definitions between the correspoding visit_start_alias_scope()
+ * call and here go out of scope and won't apply in later code any more.
+ */
+void visit_end_alias_scope(Visitor *v);
+
 /*
  * Visit an enum value.
  *
diff --git a/qapi/qapi-visit-core.c b/qapi/qapi-visit-core.c
index 7e5f40e7f0..719a9f5da2 100644
--- a/qapi/qapi-visit-core.c
+++ b/qapi/qapi-visit-core.c
@@ -135,6 +135,27 @@ bool visit_optional(Visitor *v, const char *name, bool *present)
     return *present;
 }
 
+void visit_define_alias(Visitor *v, const char *alias, const char **source)
+{
+    if (v->define_alias) {
+        v->define_alias(v, alias, source);
+    }
+}
+
+void visit_start_alias_scope(Visitor *v)
+{
+    if (v->start_alias_scope) {
+        v->start_alias_scope(v);
+    }
+}
+
+void visit_end_alias_scope(Visitor *v)
+{
+    if (v->end_alias_scope) {
+        v->end_alias_scope(v);
+    }
+}
+
 bool visit_is_input(Visitor *v)
 {
     return v->type == VISITOR_INPUT;
-- 
2.28.0