Config: Drop requirement for versions to be registered in sequence

Checking the versions at Deploy is much saner.

config/versions/versions.go

@@ -17,6 +17,7 @@ import (
 	"errors"
 	"fmt"
 	"log"
+	"slices"
 	"strconv"
 	"sync"
 
@@ -26,8 +27,8 @@ import (
 
 var (
 	errRegisteringVersion  = errors.New("error registering config version")
+	errMissingVersion      = errors.New("missing version")
 	errVersionIncompatible = errors.New("version does not implement ConfigVersion or ExchangeVersion")
-	errVersionSequence     = errors.New("version registered out of sequence")
 	errModifyingExchange   = errors.New("error modifying exchange config")
 	errNoVersions          = errors.New("error retrieving latest config version: No config versions are registered")
 	errApplyingVersion     = errors.New("error applying version")
@@ -50,23 +51,22 @@ type ExchangeVersion interface {
 type manager struct {
 	m        sync.RWMutex
 	versions []any
-	errors   error
 }
 
 // Manager is a public instance of the config version manager
 var Manager = &manager{}
 
 // Deploy upgrades or downgrades the config between versions
-// Will immediately return any errors encountered in registerVersion calls
 func (m *manager) Deploy(ctx context.Context, j []byte) ([]byte, error) {
-	if m.errors != nil {
-		return j, m.errors
+	if err := m.checkVersions(); err != nil {
+		return j, err
 	}
 
 	target, err := m.latest()
 	if err != nil {
 		return j, err
 	}
+
 	m.m.RLock()
 	defer m.m.RUnlock()
 
@@ -163,22 +163,13 @@ func exchangeDeploy(ctx context.Context, patch ExchangeVersion, method func(Exch
 }
 
 // registerVersion takes instances of config versions and adds them to the registry
-// Versions should be added sequentially without gaps, in import.go init
-// Any errors will also added to the registry for reporting later
 func (m *manager) registerVersion(ver int, v any) {
 	m.m.Lock()
 	defer m.m.Unlock()
-	switch v.(type) {
-	case ExchangeVersion, ConfigVersion:
-	default:
-		m.errors = common.AppendError(m.errors, fmt.Errorf("%w: %v", errVersionIncompatible, ver))
-		return
-	}
-	if len(m.versions) != ver {
-		m.errors = common.AppendError(m.errors, fmt.Errorf("%w: %v", errVersionSequence, ver))
-		return
+	if ver >= len(m.versions) {
+		m.versions = slices.Grow(m.versions, ver+1)[:ver+1]
 	}
-	m.versions = append(m.versions, v)
+	m.versions[ver] = v
 }
 
 // latest returns the highest version number
@@ -190,3 +181,20 @@ func (m *manager) latest() (int, error) {
 	}
 	return len(m.versions) - 1, nil
 }
+
+// checkVersions ensures that registered versions are consistent
+func (m *manager) checkVersions() error {
+	m.m.RLock()
+	defer m.m.RUnlock()
+	for ver, v := range m.versions {
+		switch v.(type) {
+		case ExchangeVersion, ConfigVersion:
+		default:
+			return fmt.Errorf("%w: %v", errVersionIncompatible, ver)
+		}
+		if v == nil {
+			return fmt.Errorf("%w: v%v", errMissingVersion, ver)
+		}
+	}
+	return nil
+}

config/versions/versions_test.go

@@ -20,7 +20,8 @@ func TestDeploy(t *testing.T) {
 	_, err = m.Deploy(context.Background(), []byte(``))
 	require.ErrorIs(t, err, errVersionIncompatible)
 
-	m.errors = nil
+	m = manager{}
+
 	m.registerVersion(0, &Version0{})
 	_, err = m.Deploy(context.Background(), []byte(`not an object`))
 	require.ErrorIs(t, err, jsonparser.KeyPathNotFoundError, "Should throw the correct error trying to add version to bad json")
@@ -81,18 +82,16 @@ func TestRegisterVersion(t *testing.T) {
 	m := manager{}
 
 	m.registerVersion(0, &Version0{})
-	require.NoError(t, m.errors)
 	assert.NotEmpty(t, m.versions)
 
-	m.errors = nil
-	m.registerVersion(1, &TestVersion1{})
-	require.ErrorIs(t, m.errors, errVersionIncompatible)
-	assert.ErrorContains(t, m.errors, ": 1")
-
-	m.errors = nil
 	m.registerVersion(2, &TestVersion2{})
-	assert.ErrorIs(t, m.errors, errVersionSequence)
-	assert.ErrorContains(t, m.errors, ": 2")
+	require.Equal(t, 3, len(m.versions), "Must allocate a space for missing version 1")
+	require.NotNil(t, m.versions[2], "Must put Version 2 in the correct slot")
+	require.Nil(t, m.versions[1], "Must leave Version 1 alone")
+
+	m.registerVersion(1, &TestVersion1{})
+	require.Equal(t, 3, len(m.versions), "Must leave len alone when registering out-of-sequence")
+	require.NotNil(t, m.versions[1], "Should put Version 1 in the correct slot")
 }
 
 func TestLatest(t *testing.T) {