compiler: circuimvent the dependency cycle v.ast <-> v.table

vlib/v/ast/ast.v

@@ -928,3 +928,19 @@ fn (stmt Stmt) position() token.Position {
 		}
 	}
 }
+
+// TODO: remove this fugly hack :-|
+// fe2ex/1 and ex2fe/1 are used to convert back and forth from 
+// table.FExpr to ast.Expr , which in turn is needed to break
+// a dependency cycle between v.ast and v.table, for the single
+// field table.Field.default_expr, which should be ast.Expr
+pub fn fe2ex(x table.FExpr) Expr {
+	res := Expr{}
+	C.memcpy(&res, &x, sizeof(Expr))
+	return res
+}
+pub fn ex2fe(x Expr) table.FExpr {
+	res := table.FExpr{}
+	C.memcpy(&res, &x, sizeof(table.FExpr))
+	return res
+}

vlib/v/gen/cgen.v

@@ -2084,7 +2084,7 @@ fn (mut g Gen) struct_init(struct_init ast.StructInit) {
 			field_name := c_name(field.name)
 			g.write('\t.$field_name = ')
 			if field.has_default_expr {
-				g.expr(field.default_expr)
+				g.expr( ast.fe2ex(field.default_expr) )
 			} else {
 				g.write(g.type_default(field.typ))
 			}
@@ -2249,12 +2249,16 @@ fn (mut g Gen) write_types(types []table.TypeSymbol) {
 				// table.Alias, table.SumType { TODO
 			}
 			table.SumType {
-				g.definitions.writeln('// Sum type')
-				g.definitions.writeln('
-				typedef struct {
-void* obj;
-int typ;
-} $name;')
+				g.definitions.writeln('')
+				g.definitions.writeln('// Sum type $name = ')
+				for sv in it.variants {
+					g.definitions.writeln('//          | ${sv:4d} = ${g.typ(sv):-20s}')
+				}
+				g.definitions.writeln('typedef struct {')
+				g.definitions.writeln('    void* obj;')
+				g.definitions.writeln('    int typ;')
+				g.definitions.writeln('} $name;')
+				g.definitions.writeln('')
 			}
 			table.ArrayFixed {
 				// .array_fixed {

vlib/v/parser/struct.v

@@ -135,7 +135,7 @@ fn (mut p Parser) struct_decl() ast.StructDecl {
 			fields << table.Field{
 				name: field_name
 				typ: typ
-				default_expr: default_expr
+				default_expr: ast.ex2fe( default_expr )
 				has_default_expr: has_default_expr
 				is_pub: is_field_pub
 				is_mut: is_field_mut

vlib/v/table/atypes.v

@@ -12,7 +12,6 @@
 module table
 
 import strings
-import v.ast
 
 pub type Type int
 
@@ -536,12 +535,17 @@ pub:
 	foo string
 }
 
+// NB: FExpr here is a actually an ast.Expr . 
+// It should always be used by casting to ast.Expr, using ast.fe2ex()/ast.ex2fe()
+// That hack is needed to break an import cycle between v.ast and v.table .
+type FExpr = voidptr | byteptr
+
 pub struct Field {
 pub:
 	name             string
 mut:
 	typ              Type
-	default_expr     ast.Expr
+	default_expr     FExpr
 	has_default_expr bool
 	default_val      string
 	attr             string