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// Copyright 2010 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package structtag defines an Analyzer that checks struct field tags
// are well formed.
package structtag
import (
"errors"
"go/ast"
"go/token"
"go/types"
"path/filepath"
"reflect"
"strconv"
"strings"
"golang.org/x/tools/go/analysis"
"golang.org/x/tools/go/analysis/passes/inspect"
"golang.org/x/tools/go/ast/inspector"
)
const Doc = `check that struct field tags conform to reflect.StructTag.Get
Also report certain struct tags (json, xml) used with unexported fields.`
var Analyzer = &analysis.Analyzer{
Name: "structtag",
Doc: Doc,
URL: "https://pkg.go.dev/golang.org/x/tools/go/analysis/passes/structtag",
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
}
var seen namesSeen
for i := 0; i < styp.NumFields(); i++ {
field := styp.Field(i)
tag := styp.Tag(i)
checkCanonicalFieldTag(pass, field, tag, &seen)
}
})
return nil, nil
}
// namesSeen keeps track of encoding tags by their key, name, and nested level
// from the initial struct. The level is taken into account because equal
// encoding key names only conflict when at the same level; otherwise, the lower
// level shadows the higher level.
type namesSeen map[uniqueName]token.Pos
type uniqueName struct {
key string // "xml" or "json"
name string // the encoding name
level int // anonymous struct nesting level
}
func (s *namesSeen) Get(key, name string, level int) (token.Pos, bool) {
if *s == nil {
*s = make(map[uniqueName]token.Pos)
}
pos, ok := (*s)[uniqueName{key, name, level}]
return pos, ok
}
func (s *namesSeen) Set(key, name string, level int, pos token.Pos) {
if *s == nil {
*s = make(map[uniqueName]token.Pos)
}
(*s)[uniqueName{key, name, level}] = pos
}
var checkTagDups = []string{"json", "xml"}
var checkTagSpaces = map[string]bool{"json": true, "xml": true, "asn1": true}
// checkCanonicalFieldTag checks a single struct field tag.
func checkCanonicalFieldTag(pass *analysis.Pass, field *types.Var, tag string, seen *namesSeen) {
switch pass.Pkg.Path() {
case "encoding/json", "encoding/xml":
// These packages know how to use their own APIs.
// Sometimes they are testing what happens to incorrect programs.
return
}
for _, key := range checkTagDups {
checkTagDuplicates(pass, tag, key, field, field, seen, 1)
}
if err := validateStructTag(tag); err != nil {
pass.Reportf(field.Pos(), "struct field tag %#q not compatible with reflect.StructTag.Get: %s", tag, err)
}
// Check for use of json or xml tags with unexported fields.
// Embedded struct. Nothing to do for now, but that
// may change, depending on what happens with issue 7363.
// TODO(adonovan): investigate, now that that issue is fixed.
if field.Anonymous() {
return
}
if field.Exported() {
return
}
for _, enc := range [...]string{"json", "xml"} {
switch reflect.StructTag(tag).Get(enc) {
// Ignore warning if the field not exported and the tag is marked as
// ignored.
case "", "-":
default:
pass.Reportf(field.Pos(), "struct field %s has %s tag but is not exported", field.Name(), enc)
return
}
}
}
// checkTagDuplicates checks a single struct field tag to see if any tags are
// duplicated. nearest is the field that's closest to the field being checked,
// while still being part of the top-level struct type.
func checkTagDuplicates(pass *analysis.Pass, tag, key string, nearest, field *types.Var, seen *namesSeen, level int) {
val := reflect.StructTag(tag).Get(key)
if val == "-" {
// Ignored, even if the field is anonymous.
return
}
if val == "" || val[0] == ',' {
if !field.Anonymous() {
// Ignored if the field isn't anonymous.
return
}
typ, ok := field.Type().Underlying().(*types.Struct)
if !ok {
return
}
for i := 0; i < typ.NumFields(); i++ {
field := typ.Field(i)
if !field.Exported() {
continue
}
tag := typ.Tag(i)
checkTagDuplicates(pass, tag, key, nearest, field, seen, level+1)
}
return
}
if key == "xml" && field.Name() == "XMLName" {
// XMLName defines the XML element name of the struct being
// checked. That name cannot collide with element or attribute
// names defined on other fields of the struct. Vet does not have a
// check for untagged fields of type struct defining their own name
// by containing a field named XMLName; see issue 18256.
return
}
if i := strings.Index(val, ","); i >= 0 {
if key == "xml" {
// Use a separate namespace for XML attributes.
for _, opt := range strings.Split(val[i:], ",") {
if opt == "attr" {
key += " attribute" // Key is part of the error message.
break
}
}
}
val = val[:i]
}
if pos, ok := seen.Get(key, val, level); ok {
alsoPos := pass.Fset.Position(pos)
alsoPos.Column = 0
// Make the "also at" position relative to the current position,
// to ensure that all warnings are unambiguous and correct. For
// example, via anonymous struct fields, it's possible for the
// two fields to be in different packages and directories.
thisPos := pass.Fset.Position(field.Pos())
rel, err := filepath.Rel(filepath.Dir(thisPos.Filename), alsoPos.Filename)
if err != nil {
// Possibly because the paths are relative; leave the
// filename alone.
} else {
alsoPos.Filename = rel
}
pass.Reportf(nearest.Pos(), "struct field %s repeats %s tag %q also at %s", field.Name(), key, val, alsoPos)
} else {
seen.Set(key, val, level, field.Pos())
}
}
var (
errTagSyntax = errors.New("bad syntax for struct tag pair")
errTagKeySyntax = errors.New("bad syntax for struct tag key")
errTagValueSyntax = errors.New("bad syntax for struct tag value")
errTagValueSpace = errors.New("suspicious space in struct tag value")
errTagSpace = errors.New("key:\"value\" pairs not separated by spaces")
)
// validateStructTag parses the struct tag and returns an error if it is not
// in the canonical format, which is a space-separated list of key:"value"
// settings. The value may contain spaces.
func validateStructTag(tag string) error {
// This code is based on the StructTag.Get code in package reflect.
n := 0
for ; tag != ""; n++ {
if n > 0 && tag != "" && tag[0] != ' ' {
// More restrictive than reflect, but catches likely mistakes
// like `x:"foo",y:"bar"`, which parses as `x:"foo" ,y:"bar"` with second key ",y".
return errTagSpace
}
// Skip leading space.
i := 0
for i < len(tag) && tag[i] == ' ' {
i++
}
tag = tag[i:]
if tag == "" {
break
}
// Scan to colon. A space, a quote or a control character is a syntax error.
// Strictly speaking, control chars include the range [0x7f, 0x9f], not just
// [0x00, 0x1f], but in practice, we ignore the multi-byte control characters
// as it is simpler to inspect the tag's bytes than the tag's runes.
i = 0
for i < len(tag) && tag[i] > ' ' && tag[i] != ':' && tag[i] != '"' && tag[i] != 0x7f {
i++
}
if i == 0 {
return errTagKeySyntax
}
if i+1 >= len(tag) || tag[i] != ':' {
return errTagSyntax
}
if tag[i+1] != '"' {
return errTagValueSyntax
}
key := tag[:i]
tag = tag[i+1:]
// Scan quoted string to find value.
i = 1
for i < len(tag) && tag[i] != '"' {
if tag[i] == '\\' {
i++
}
i++
}
if i >= len(tag) {
return errTagValueSyntax
}
qvalue := tag[:i+1]
tag = tag[i+1:]
value, err := strconv.Unquote(qvalue)
if err != nil {
return errTagValueSyntax
}
if !checkTagSpaces[key] {
continue
}
switch key {
case "xml":
// If the first or last character in the XML tag is a space, it is
// suspicious.
if strings.Trim(value, " ") != value {
return errTagValueSpace
}
// If there are multiple spaces, they are suspicious.
if strings.Count(value, " ") > 1 {
return errTagValueSpace
}
// If there is no comma, skip the rest of the checks.
comma := strings.IndexRune(value, ',')
if comma < 0 {
continue
}
// If the character before a comma is a space, this is suspicious.
if comma > 0 && value[comma-1] == ' ' {
return errTagValueSpace
}
value = value[comma+1:]
case "json":
// JSON allows using spaces in the name, so skip it.
comma := strings.IndexRune(value, ',')
if comma < 0 {
continue
}
value = value[comma+1:]
}
if strings.IndexByte(value, ' ') >= 0 {
return errTagValueSpace
}
}
return nil
}