pkg/compiler: support if[expr] attributes

The expression may either include integers/consts or reference other
fields in the structure via value[field1:field2:field3].

The fields on this path must all belong to structures and must not have
any if conditions themselves.

For unions, mandate that the last field has no conditions (it will be
the default one).

For structs, convert conditional fields into fields of a union type of
the following form:

anonymous_union [
 value T (if[expression])
 void void
]

1 files changed, 57 insertions, 0 deletions

diff --git a/prog/types.go b/prog/types.go
index ce02d2d21..73fa3a972 100644
--- a/prog/types.go
+++ b/prog/types.go
@@ -72,6 +72,7 @@ type Field struct {
 	Type
 	HasDirection bool
 	Direction    Dir
+	Condition    Expression
 }
 
 func (f *Field) Dir(def Dir) Dir {
@@ -81,6 +82,62 @@ func (f *Field) Dir(def Dir) Dir {
 	return def
 }
 
+type Expression interface {
+	fmt.GoStringer
+	ForEachValue(func(*Value))
+	Clone() Expression
+}
+
+type BinaryOperator int
+
+const (
+	OperatorCompareEq BinaryOperator = iota
+	OperatorCompareNeq
+	OperatorBinaryAnd
+)
+
+type BinaryExpression struct {
+	Operator BinaryOperator
+	Left     Expression
+	Right    Expression
+}
+
+func (bo BinaryExpression) GoString() string {
+	return fmt.Sprintf("&prog.BinaryExpression{%#v,%#v,%#v}", bo.Operator, bo.Left, bo.Right)
+}
+
+func (bo BinaryExpression) ForEachValue(cb func(*Value)) {
+	bo.Left.ForEachValue(cb)
+	bo.Right.ForEachValue(cb)
+}
+
+func (bo *BinaryExpression) Clone() Expression {
+	return &BinaryExpression{
+		Operator: bo.Operator,
+		Left:     bo.Left.Clone(),
+		Right:    bo.Right.Clone(),
+	}
+}
+
+type Value struct {
+	// If Path is empty, Value is to be used.
+	Value uint64
+	// Path to the field.
+	Path []string
+}
+
+func (v Value) GoString() string {
+	return fmt.Sprintf("&prog.Value{%#v,%#v}", v.Value, v.Path)
+}
+
+func (v *Value) ForEachValue(cb func(*Value)) {
+	cb(v)
+}
+
+func (v *Value) Clone() Expression {
+	return &Value{v.Value, append([]string{}, v.Path...)}
+}
+
 type BinaryFormat int
 
 const (