simplify YAML field changes detection

internals/plan/extensions_test.go

@@ -35,8 +35,8 @@ type inputLayer struct {
 }
 
 // PlanResult represents the final content of a combined plan. Since this
-// package exclusively focuses extensions, all built-in sections are empty
-// and ignored in the test results.
+// test file exclusively focuses on extensions, all built-in sections are
+// empty and ignored in the test results.
 type planResult struct {
 	x *xSection
 	y *ySection

internals/plan/plan.go

@@ -1251,11 +1251,6 @@ func ParseLayer(order int, label string, data []byte) (*Layer, error) {
 		"checks":      &layer.Checks,
 		"log-targets": &layer.LogTargets,
 	}
-	// Make sure builtins contains the exact same fields as expected
-	// in the Layer type.
-	if !mapMatchKeys(builtins, builtinSections) {
-		panic("internal error: parsed fields and layer fields differ")
-	}
 
 	sections := make(map[string]yaml.Node)
 	// Deliberately pre-allocate at least an empty yaml.Node for every
@@ -1340,20 +1335,6 @@ func ParseLayer(order int, label string, data []byte) (*Layer, error) {
 	return layer, err
 }
 
-// mapMatchKeys returns true if the key list supplied is an exact match of the
-// keys in the map (ordering is ignored).
-func mapMatchKeys[M ~map[K]V, K comparable, V any](inMap M, keyList []K) bool {
-	if len(inMap) != len(keyList) {
-		return false
-	}
-	for key, _ := range inMap {
-		if !slices.Contains(keyList, key) {
-			return false
-		}
-	}
-	return true
-}
-
 func validServiceAction(action ServiceAction, additionalValid ...ServiceAction) bool {
 	for _, v := range additionalValid {
 		if action == v {

internals/plan/plan_test.go

@@ -20,7 +20,6 @@ import (
 	"os"
 	"path/filepath"
 	"reflect"
-	"slices"
 	"strings"
 	"time"
 	"unicode"
@@ -29,6 +28,7 @@ import (
 	"gopkg.in/yaml.v3"
 
 	"github.com/canonical/pebble/internals/plan"
+	"github.com/canonical/pebble/internals/testutil"
 )
 
 const (
@@ -2072,14 +2072,15 @@ func (s *S) TestStartStopOrderMultipleLanes(c *C) {
 	c.Assert(lanes[2], DeepEquals, []string{"srv3"})
 }
 
-// TestLayerBuiltinCompatible ensures layerBuiltins used in the plan package
-// reflects the same YAML fields as exposed in the Layer type.
-func (s *S) TestLayerBuiltinCompatible(c *C) {
-	fields := structYamlFields(plan.Layer{})
-	c.Assert(len(fields), Equals, len(plan.BuiltinSections))
-	for _, field := range fields {
-		c.Assert(slices.Contains(plan.BuiltinSections, field), Equals, true)
-	}
+// TestSectionFieldStability detects changes in plan.Layer and plan.Plan
+// YAML fields, and fails on any change that could break hardcoded section
+// fields in the code. On failure, please carefully inspect and update
+// the plan library where required.
+func (s *S) TestSectionFieldStability(c *C) {
+	layerFields := structYamlFields(plan.Layer{})
+	c.Assert(layerFields, testutil.DeepUnsortedMatches, []string{"summary", "description", "services", "checks", "log-targets", "sections"})
+	planFields := structYamlFields(plan.Plan{})
+	c.Assert(planFields, testutil.DeepUnsortedMatches, []string{"services", "checks", "log-targets", "sections"})
 }
 
 // structYamlFields extracts the YAML fields from a struct. If the YAML tag
@@ -2090,7 +2091,7 @@ func structYamlFields(inStruct any) []string {
 	for i := range inStructType.NumField() {
 		fieldType := inStructType.Field(i)
 		yamlTag := fieldType.Tag.Get("yaml")
-		if fieldType.IsExported() && yamlTag != "-" && !strings.Contains(yamlTag, ",inline") {
+		if fieldType.IsExported() && yamlTag != "-" {
 			tag, _, _ := strings.Cut(fieldType.Tag.Get("yaml"), ",")
 			if tag == "" {
 				tag = firstLetterToLower(fieldType.Name)