Ignore complexity of children in maps/slices (#382)

When considering inlining maps/slices/arrays, apply a fixed cost and ignore the cost of the children.

If children are too expensive, they will not be inlined, but it shouldn't affect whether the map itself is inlined.

This only really applies when a map or slice type is aliased, otherwise it will not be considered for inlining.

Fixes #381

Author: klauspost

Diff for: _generated/def.go

@@ -308,3 +308,19 @@ type NumberJSONSample struct {
 	Map    map[string]json.Number
 	OE     json.Number `msg:",omitempty"`
 }
+
+type Flobbity struct {
+	A Flobs `msg:"a,omitempty"`
+	B Flobs `msg:"b,omitempty"`
+}
+
+type Flobs []Flob
+
+type Flob struct {
+	X Numberwang `msg:"x"`
+	Y int8       `msg:"y"`
+	Z int8       `msg:"z"`
+	W int32      `msg:"w"`
+}
+
+type Numberwang int8

Diff for: gen/elem.go

@@ -268,7 +268,10 @@ func (a *Array) Copy() Elem {
 	return &b
 }
 
-func (a *Array) Complexity() int { return 1 + a.Els.Complexity() }
+func (a *Array) Complexity() int {
+	// We consider the complexity constant and leave the children to decide on their own.
+	return 2
+}
 
 // ZeroExpr returns the zero/empty expression or empty string if not supported.  Unsupported for this case.
 func (a *Array) ZeroExpr() string { return "" }
@@ -313,7 +316,10 @@ func (m *Map) Copy() Elem {
 	return &g
 }
 
-func (m *Map) Complexity() int { return 2 + m.Value.Complexity() }
+func (m *Map) Complexity() int {
+	// Complexity of maps are considered constant. Children should decide on their own.
+	return 3
+}
 
 // ZeroExpr returns the zero/empty expression or empty string if not supported.  Always "nil" for this case.
 func (m *Map) ZeroExpr() string { return "nil" }
@@ -360,7 +366,8 @@ func (s *Slice) Copy() Elem {
 }
 
 func (s *Slice) Complexity() int {
-	return 1 + s.Els.Complexity()
+	// We leave the inlining decision to the slice children.
+	return 2
 }
 
 // ZeroExpr returns the zero/empty expression or empty string if not supported.  Always "nil" for this case.