json: remove cycle detection from constructStructType (ignore-whitespace)

This responsibility was moved to constructCodec.

Author: extemporalgenome

json/codec.go

@@ -516,42 +516,35 @@ func constructStructCodec(t reflect.Type, seen codecCache, canAddr bool) codec {
 }
 
 func constructStructType(t reflect.Type, seen codecCache, canAddr bool) *structType {
-	// Used for preventing infinite recursion on types that have pointers to
-	// themselves.
-	st := seen[t]
-
-	if st == nil {
-		st = &structType{
-			fields:      make([]structField, 0, t.NumField()),
-			fieldsIndex: make(map[string]*structField),
-			ficaseIndex: make(map[string]*structField),
-			typ:         t,
-		}
-
-		seen[t] = st
-		st.fields = appendStructFields(st.fields, t, 0, seen, canAddr)
-
-		for i := range st.fields {
-			f := &st.fields[i]
-			s := strings.ToLower(f.name)
-			st.fieldsIndex[f.name] = f
-			// When there is ambiguity because multiple fields have the same
-			// case-insensitive representation, the first field must win.
-			if _, exists := st.ficaseIndex[s]; !exists {
-				st.ficaseIndex[s] = f
-			}
+	st := &structType{
+		fields:      make([]structField, 0, t.NumField()),
+		fieldsIndex: make(map[string]*structField),
+		ficaseIndex: make(map[string]*structField),
+		typ:         t,
+	}
+
+	st.fields = appendStructFields(st.fields, t, 0, seen, canAddr)
+
+	for i := range st.fields {
+		f := &st.fields[i]
+		s := strings.ToLower(f.name)
+		st.fieldsIndex[f.name] = f
+		// When there is ambiguity because multiple fields have the same
+		// case-insensitive representation, the first field must win.
+		if _, exists := st.ficaseIndex[s]; !exists {
+			st.ficaseIndex[s] = f
 		}
+	}
 
-		// At a certain point the linear scan provided by keyset is less
-		// efficient than a map. The 32 was chosen based on benchmarks in the
-		// segmentio/asm repo run with an Intel Kaby Lake processor and go1.17.
-		if len(st.fields) <= 32 {
-			keys := make([][]byte, len(st.fields))
-			for i, f := range st.fields {
-				keys[i] = []byte(f.name)
-			}
-			st.keyset = keyset.New(keys)
+	// At a certain point the linear scan provided by keyset is less
+	// efficient than a map. The 32 was chosen based on benchmarks in the
+	// segmentio/asm repo run with an Intel Kaby Lake processor and go1.17.
+	if len(st.fields) <= 32 {
+		keys := make([][]byte, len(st.fields))
+		for i, f := range st.fields {
+			keys[i] = []byte(f.name)
 		}
+		st.keyset = keyset.New(keys)
 	}
 
 	return st