Keep one list of credential forms in the catalogue, so no reader of a plan refuses a form another writes (issue 774)

Second meeting of the credential-form list kind: the provisioner client's
own copy lacked "none" and refused every plan naming it, as the
controller's had before. Thorough: one list in mesh-sdk,
catalogue.CredentialForms and IsCredentialForm; provisions' forms are now
the catalogue's constants.

go/catalogue/handed_providers_test.go

@@ -153,6 +153,13 @@ func TestAHandedModulesPlanNamesTheCredentialFormOfItsProvidersOffer(t *testing.
 		if len(got) != 1 || got[0].CredentialForm != want {
 			t.Errorf("an offer with %q: the plan names %+v, want the form %q", credential, got, want)
 		}
+		// Every form a plan names is in the one list each reader checks (issue 774); an undeclared one is not.
+		if IsCredentialForm(want) != (want != "") {
+			t.Errorf("the form %q of an offer with %q: in CredentialForms %v", want, credential, IsCredentialForm(want))
+		}
+	}
+	if forms := strings.Join(CredentialForms(), ","); forms != "shared,pair,issued,given,none" || IsCredentialForm("maybe") {
+		t.Errorf("the credential forms are %s, and maybe is one: %v", forms, IsCredentialForm("maybe"))
 	}
 	if got := (Manifest{Module: "x"}).CredentialFormOf("postgres-database"); got != "" {
 		t.Errorf("a module offering nothing has the credential form %q", got)

go/catalogue/manifest.go

@@ -11,6 +11,7 @@ import (
 	"errors"
 	"fmt"
 	"regexp"
+	"slices"
 	"sort"
 	"strconv"
 	"strings"
@@ -371,6 +372,17 @@ const (
 	CredentialFormNone = "none"
 )
 
+// CredentialForms is the one list of the credential forms a plan's entry may name (issue 774): every part that reads
+// a plan checks a form here, so a form added above reaches each of them at once. Each part kept its own copy before,
+// and a copy left without "none" refused every plan naming it.
+func CredentialForms() []string {
+	return []string{CredentialFormShared, CredentialFormPair, CredentialFormIssued, CredentialFormGiven,
+		CredentialFormNone}
+}
+
+// IsCredentialForm is whether form is one of CredentialForms.
+func IsCredentialForm(form string) bool { return slices.Contains(CredentialForms(), form) }
+
 // CredentialFormOf is the credential form this module's offer of a provision declares, read from the offer's
 // `credential` alone (issue 768): no new manifest field, since that field already says whether the provider shares
 // one of its own secrets, its software issues it, or a person gives it, and saying none is a login per consumer.

go/provisions/provisions.go

@@ -93,15 +93,16 @@ func PlanKey(node, module string) (string, error) {
 	return node + "." + module, nil
 }
 
-// The forms of a provision's credential, as a plan's entry names them (catalogue.PlanProvision.CredentialForm).
+// The forms of a provision's credential, as a plan's entry names them (catalogue.PlanProvision.CredentialForm): the
+// catalogue's one list (catalogue.CredentialForms, issue 774), under the names this package has used.
 const (
-	FormPair   = "pair"
-	FormShared = "shared"
-	FormIssued = "issued"
-	FormGiven  = "given"
+	FormPair   = catalogue.CredentialFormPair
+	FormShared = catalogue.CredentialFormShared
+	FormIssued = catalogue.CredentialFormIssued
+	FormGiven  = catalogue.CredentialFormGiven
 	// FormNone is an offer whose consumers present no credential (catalogue.CredentialFormNone): the vault mints nothing,
 	// and the provision depends on no credential.
-	FormNone = "none"
+	FormNone = catalogue.CredentialFormNone
 )
 
 // VaultName is the vault's name of a provision's credential in form, as its verb `own` names it and the provider asks