Code

cmd/validjson/main.go

@@ -0,0 +1,10 @@
+package main
+
+import (
+	"github.com/matthewloring/validjson"
+	"golang.org/x/tools/go/analysis/singlechecker"
+)
+
+func main() {
+	singlechecker.Main(validjson.Analyzer)
+}

go.mod

@@ -0,0 +1,5 @@
+module github.com/matthewloring/validjson
+
+go 1.13
+
+require golang.org/x/tools v0.0.0-20200124220429-8fe064f891f2

go.sum

@@ -0,0 +1,12 @@
+golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
+golang.org/x/crypto v0.0.0-20191011191535-87dc89f01550/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=
+golang.org/x/mod v0.1.1-0.20191105210325-c90efee705ee/go.mod h1:QqPTAvyqsEbceGzBzNggFXnrqF1CaUcvgkdR5Ot7KZg=
+golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
+golang.org/x/net v0.0.0-20190620200207-3b0461eec859/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
+golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
+golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
+golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
+golang.org/x/tools v0.0.0-20200124220429-8fe064f891f2 h1:ZNYGPNJ+tKwnFHzxlFH8bZSIj5uyr3xdUscYDsKQJ1k=
+golang.org/x/tools v0.0.0-20200124220429-8fe064f891f2/go.mod h1:TB2adYChydJhpapKDTa4BR/hXlZSLoq2Wpct/0txZ28=
+golang.org/x/xerrors v0.0.0-20191011141410-1b5146add898/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=

testdata/src/a/a.go

@@ -0,0 +1,32 @@
+// This file contains the test for valid json tags.
+
+package a
+
+type Key struct {
+	A, B string
+}
+
+type StrAlias string
+
+type ChanAlias chan<- int
+
+type ValidJsonTest struct {
+	A int                           `json:"A"`
+	B int                           `json:"B,omitempty"`
+	C int                           `json:",omitempty"`
+	D int                           `json:"-"`
+	E chan<- int                    `json:"E"` // want "struct field has json tag but non-serializable type chan<- int"
+	F chan<- int                    `json:"-"`
+	G chan<- int                    `json:"-,"` // want "struct field has json tag but non-serializable type chan<- int"
+	H ChanAlias                     `json:"H"`  // want "struct field has json tag but non-serializable type a.ChanAlias"
+	I map[int]int                   `json:"I"`
+	J map[int64]int                 `json:"J"`
+	K map[Key]int                   `json:"K"` // want "struct field has json tag but non-serializable type"
+	L map[struct{ A, B string }]int `json:"L"` // want "struct field has json tag but non-serializable type"
+	M map[string]int                `json:"M"`
+	N map[StrAlias]int              `json:"N"`
+	O func()                        `json:"O"` // want "struct field has json tag but non-serializable type func()"
+	P complex64                     `json:"P"` // want "struct field has json tag but non-serializable type complex64"
+	Q complex128                    `json:"Q"` // want "struct field has json tag but non-serializable type complex128"
+	R StrAlias                      `json:"R"`
+}

validjson.go

@@ -0,0 +1,75 @@
+// Package validjson defines an Analyzer that checks that struct fields
+// with json tags have json serializable types.
+package validjson
+
+import (
+	"go/ast"
+	"go/types"
+	"reflect"
+
+	"golang.org/x/tools/go/analysis"
+	"golang.org/x/tools/go/analysis/passes/inspect"
+	"golang.org/x/tools/go/ast/inspector"
+)
+
+var Analyzer = &analysis.Analyzer{
+	Name:             "validjson",
+	Doc:              "check that struct fields with json tags have json-compatible types.",
+	Requires:         []*analysis.Analyzer{inspect.Analyzer},
+	RunDespiteErrors: true,
+	Run:              run,
+}
+
+func run(pass *analysis.Pass) (interface{}, error) {
+	inspect := pass.ResultOf[inspect.Analyzer].(*inspector.Inspector)
+
+	nodeFilter := []ast.Node{
+		(*ast.StructType)(nil),
+	}
+	inspect.Preorder(nodeFilter, func(n ast.Node) {
+		styp, ok := pass.TypesInfo.Types[n.(*ast.StructType)].Type.(*types.Struct)
+		// Type information may be incomplete.
+		if !ok {
+			return
+		}
+		for i := 0; i < styp.NumFields(); i++ {
+			f := styp.Field(i)
+			if isNonSkipJSONTag(styp.Tag(i)) && !isJSONSerializable(f.Type()) {
+				pass.Reportf(f.Pos(), "struct field has json tag but non-serializable type %v", f.Type())
+			}
+		}
+	})
+	return nil, nil
+}
+
+// See: https://blog.golang.org/json-and-go
+func isJSONSerializable(t types.Type) bool {
+	switch fieldType := t.(type) {
+	case *types.Basic:
+		return fieldType.Kind() != types.Complex64 && fieldType.Kind() != types.Complex128
+	case *types.Chan:
+		return false
+	case *types.Map:
+		return isJSONSerializableAsMapKey(fieldType.Key())
+	case *types.Named:
+		return isJSONSerializable(fieldType.Underlying())
+	case *types.Signature:
+		return false
+	}
+	return true
+}
+
+func isJSONSerializableAsMapKey(t types.Type) bool {
+	switch keyType := t.(type) {
+	case *types.Basic:
+		return keyType.Info()&types.IsInteger != 0 || keyType.Kind() == types.String
+	case *types.Named:
+		return isJSONSerializableAsMapKey(keyType.Underlying())
+	}
+	return false
+}
+
+func isNonSkipJSONTag(tag string) bool {
+	val, found := (reflect.StructTag)(tag).Lookup("json")
+	return found && val != "-"
+}

validjson_test.go

@@ -0,0 +1,13 @@
+package validjson_test
+
+import (
+	"testing"
+
+	"github.com/matthewloring/validjson"
+	"golang.org/x/tools/go/analysis/analysistest"
+)
+
+func Test(t *testing.T) {
+	testdata := analysistest.TestData()
+	analysistest.Run(t, testdata, validjson.Analyzer, "a")
+}