sys: support type aliases (aka typedefs)

Complex types that are often repeated can be given short type aliases using the
following syntax:

```
type identifier underlying_type
```

For example:

```
type signalno int32[0:65]
type net_port proc[20000, 4, int16be]
```

Then, type alias can be used instead of the underlying type in any contexts.
Underlying type needs to be described as if it's a struct field, that is,
with the base type if it's required. However, type alias can be used as syscall
arguments as well. Underlying types are currently restricted to integer types,
`ptr`, `ptr64`, `const`, `flags` and `proc` types.

1 files changed, 14 insertions, 0 deletions

diff --git a/pkg/ast/ast.go b/pkg/ast/ast.go
index 4c9101f79..9e87a1b81 100644
--- a/pkg/ast/ast.go
+++ b/pkg/ast/ast.go
@@ -20,6 +20,10 @@ type Description struct {
 // Node is AST node interface.
 type Node interface {
 	Info() (pos Pos, typ string, name string)
+	// Clone makes a deep copy of the node.
+	// If newPos is not zero, sets Pos of all nodes to newPos.
+	// If newPos is zero, Pos of nodes is left intact.
+	Clone(newPos Pos) Node
 }
 
 // Top-level AST nodes:
@@ -130,6 +134,16 @@ func (n *StrFlags) Info() (Pos, string, string) {
 	return n.Pos, "string flags", n.Name.Name
 }
 
+type TypeDef struct {
+	Pos  Pos
+	Name *Ident
+	Type *Type
+}
+
+func (n *TypeDef) Info() (Pos, string, string) {
+	return n.Pos, "type", n.Name.Name
+}
+
 // Not top-level AST nodes:
 
 type Ident struct {