Improvements to kyaml fn framework

This commit creates a new version of the alpha configuration functions framework. Goals include:
- Make it easy to build multi-version APIs with the framework (not previously facilitated at all).
- Simplify the framework's APIs where redundant configuration options exist (leaving the most powerful, replacing others with helpers to maintain usability they provided).
- Make the Framework's APIs more consistent (e.g. between the various template types, usage of kio.Filter, field names)
- Decouple responsibilities (e.g. command creation, resource list processing, generation of templating functions).
- Make the framework even more powerfully pluggable (e.g. any kio.Filter can be a selector, and the selector the framework provides is itself a filter built from reusable abstractions).
- Improve documentation.
- Make container patches merge fields (notably list fields like `env`) correctly.

kyaml/fn/framework/result.go

@@ -0,0 +1,98 @@
+// Copyright 2019 The Kubernetes Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+package framework
+
+import (
+	"fmt"
+	"strings"
+
+	"sigs.k8s.io/kustomize/kyaml/yaml"
+)
+
+// Severity indicates the severity of the Result
+type Severity string
+
+const (
+	// Error indicates the result is an error.  Will cause the function to exit non-0.
+	Error Severity = "error"
+	// Warning indicates the result is a warning
+	Warning Severity = "warning"
+	// Info indicates the result is an informative message
+	Info Severity = "info"
+)
+
+// ResultItem defines a validation result
+type ResultItem struct {
+	// Message is a human readable message
+	Message string `yaml:"message,omitempty"`
+
+	// Severity is the severity of this result
+	Severity Severity `yaml:"severity,omitempty"`
+
+	// ResourceRef is a reference to a resource
+	ResourceRef yaml.ResourceMeta `yaml:"resourceRef,omitempty"`
+
+	// Field is a reference to the field in a resource this result refers to
+	Field Field `yaml:"field,omitempty"`
+
+	// File references a file containing the resource this result refers to
+	File File `yaml:"file,omitempty"`
+}
+
+// String provides a human-readable message for the result item
+func (i ResultItem) String() string {
+	identifier := i.ResourceRef.GetIdentifier()
+	idString := strings.Join([]string{identifier.GetAPIVersion(), identifier.GetKind(), identifier.GetNamespace(), identifier.GetName()}, "/")
+	return fmt.Sprintf("[%s] %s %s: %s", i.Severity, idString, i.Field.Path, i.Message)
+}
+
+// File references a file containing a resource
+type File struct {
+	// Path is relative path to the file containing the resource
+	Path string `yaml:"path,omitempty"`
+
+	// Index is the index into the file containing the resource
+	// (i.e. if there are multiple resources in a single file)
+	Index int `yaml:"index,omitempty"`
+}
+
+// Field references a field in a resource
+type Field struct {
+	// Path is the field path
+	Path string `yaml:"path,omitempty"`
+
+	// CurrentValue is the current field value
+	CurrentValue string `yaml:"currentValue,omitempty"`
+
+	// SuggestedValue is the suggested field value
+	SuggestedValue string `yaml:"suggestedValue,omitempty"`
+}
+
+// Result defines a function result which will be set on the emitted ResourceList
+type Result struct {
+	// Name is the name of the function creating the result
+	Name string `yaml:"name,omitempty"`
+
+	// Items are the individual results
+	Items []ResultItem `yaml:"items,omitempty"`
+}
+
+// Error enables a Result to be returned as an error
+func (e Result) Error() string {
+	var msgs []string
+	for _, i := range e.Items {
+		msgs = append(msgs, i.String())
+	}
+	return strings.Join(msgs, "\n\n")
+}
+
+// ExitCode provides the exit code based on the result's severity
+func (e Result) ExitCode() int {
+	for _, i := range e.Items {
+		if i.Severity == Error {
+			return 1
+		}
+	}
+	return 0
+}