config/validate: add new config validator

This validator is still experimental and is going to need new rules in the
future. This lays out the general framework.

config/validate/report.go

@@ -0,0 +1,90 @@
+/*
+   Copyright 2014 CoreOS, Inc.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package validate
+
+import (
+	"encoding/json"
+	"fmt"
+)
+
+// Report represents the list of entries resulting from validation.
+type Report struct {
+	entries []Entry
+}
+
+// Error adds an error entry to the report.
+func (r *Report) Error(line int, message string) {
+	r.entries = append(r.entries, Entry{entryError, message, line})
+}
+
+// Warning adds a warning entry to the report.
+func (r *Report) Warning(line int, message string) {
+	r.entries = append(r.entries, Entry{entryWarning, message, line})
+}
+
+// Info adds an info entry to the report.
+func (r *Report) Info(line int, message string) {
+	r.entries = append(r.entries, Entry{entryInfo, message, line})
+}
+
+// Entries returns the list of entries in the report.
+func (r *Report) Entries() []Entry {
+	return r.entries
+}
+
+// Entry represents a single generic item in the report.
+type Entry struct {
+	kind    entryKind
+	message string
+	line    int
+}
+
+// String returns a human-readable representation of the entry.
+func (e Entry) String() string {
+	return fmt.Sprintf("line %d: %s: %s", e.line, e.kind, e.message)
+}
+
+// MarshalJSON satisfies the json.Marshaler interface, returning the entry
+// encoded as a JSON object.
+func (e Entry) MarshalJSON() ([]byte, error) {
+	return json.Marshal(map[string]interface{}{
+		"kind":    e.kind.String(),
+		"message": e.message,
+		"line":    e.line,
+	})
+}
+
+type entryKind int
+
+const (
+	entryError entryKind = iota
+	entryWarning
+	entryInfo
+)
+
+func (k entryKind) String() string {
+	switch k {
+	case entryError:
+		return "error"
+	case entryWarning:
+		return "warning"
+	case entryInfo:
+		return "info"
+	default:
+		panic(fmt.Sprintf("invalid kind %d", k))
+	}
+}