struct-tag (new rule) (#47)

rule/struct-tag.go

@@ -0,0 +1,167 @@
+package rule
+
+import (
+	"fmt"
+	"github.com/fatih/structtag"
+	"github.com/mgechev/revive/lint"
+	"go/ast"
+	"strconv"
+	"strings"
+)
+
+// StructTagRule lints struct tags.
+type StructTagRule struct{}
+
+// Apply applies the rule to given file.
+func (r *StructTagRule) Apply(file *lint.File, _ lint.Arguments) []lint.Failure {
+	var failures []lint.Failure
+
+	onFailure := func(failure lint.Failure) {
+		failures = append(failures, failure)
+	}
+
+	w := lintStructTagRule{onFailure: onFailure}
+
+	ast.Walk(w, file.AST)
+
+	return failures
+}
+
+// Name returns the rule name.
+func (r *StructTagRule) Name() string {
+	return "struct-tag"
+}
+
+type lintStructTagRule struct {
+	onFailure func(lint.Failure)
+}
+
+func (w lintStructTagRule) Visit(node ast.Node) ast.Visitor {
+	switch n := node.(type) {
+	case *ast.StructType:
+		if n.Fields == nil || n.Fields.NumFields() < 1 {
+			return nil // skip empty structs
+		}
+
+		for _, f := range n.Fields.List {
+			if f.Tag != nil {
+				w.checkTaggedField(f)
+			}
+		}
+	}
+
+	return w
+
+}
+
+// checkTaggedField checks the tag of the given field.
+// precondition: the field has a tag
+func (w lintStructTagRule) checkTaggedField(f *ast.Field) {
+	tags, err := structtag.Parse(strings.Trim(f.Tag.Value, "`"))
+	if err != nil || tags == nil {
+		return
+	}
+
+	for _, tag := range tags.Tags() {
+		switch key := tag.Key; key {
+		case "asn1":
+			// Not implemented yet
+		case "default":
+			if !w.typeValueMatch(f.Type, tag.Name) {
+				w.addFailure(f.Tag, "field's type and default value's type mismatch")
+			}
+		case "json":
+			msg, ok := w.checkJSONTag(tag.Options)
+			if !ok {
+				w.addFailure(f.Tag, msg)
+			}
+		case "protobuf":
+			// Not implemented yet
+		case "required":
+			if tag.Name != "true" && tag.Name != "false" {
+				w.addFailure(f.Tag, "required should be 'true' or 'false'")
+			}
+		case "xml":
+			msg, ok := w.checkXMLTag(tag.Options)
+			if !ok {
+				w.addFailure(f.Tag, msg)
+			}
+		case "yaml":
+			msg, ok := w.checkYAMLTag(tag.Options)
+			if !ok {
+				w.addFailure(f.Tag, msg)
+			}
+		default:
+			// unknown key
+		}
+	}
+}
+
+func (w lintStructTagRule) checkJSONTag(options []string) (string, bool) {
+	for _, opt := range options {
+		switch opt {
+		case "omitempty", "string":
+		default:
+			return fmt.Sprintf("unknown option '%s' in JSON tag", opt), false
+		}
+	}
+
+	return "", true
+}
+
+func (w lintStructTagRule) checkXMLTag(options []string) (string, bool) {
+	for _, opt := range options {
+		switch opt {
+		case "attr", "cdata", "chardata", "innerxml", "comment", "any", "omitempty":
+		default:
+			return fmt.Sprintf("unknown option '%s' in XML tag", opt), false
+		}
+	}
+
+	return "", true
+}
+
+func (w lintStructTagRule) checkYAMLTag(options []string) (string, bool) {
+	for _, opt := range options {
+		switch opt {
+		case "flow", "inline", "omitempty":
+		default:
+			return fmt.Sprintf("unknown option '%s' in YAML tag", opt), false
+		}
+	}
+
+	return "", true
+}
+
+func (w lintStructTagRule) typeValueMatch(t ast.Expr, val string) bool {
+	tID, ok := t.(*ast.Ident)
+	if !ok {
+		return true
+	}
+
+	typeMatches := true
+	switch tID.Name {
+	case "bool":
+		typeMatches = val == "true" || val == "false"
+	case "float64":
+		_, err := strconv.ParseFloat(val, 64)
+		typeMatches = err == nil
+	case "int":
+		_, err := strconv.ParseInt(val, 10, 64)
+		typeMatches = err == nil
+	case "string":
+	case "nil":
+	default:
+		// unchecked type
+	}
+
+	return typeMatches
+}
+
+func (w lintStructTagRule) addFailure(n ast.Node, msg string) {
+	w.onFailure(lint.Failure{
+		Node:       n,
+		Failure:    msg,
+		Confidence: 1,
+	})
+}