fix: ensure topic name matches idiomatic variable name (#1958)

Fixes #1919

backend/controller/pubsub/testdata/go/publisher/publisher.go

@@ -9,7 +9,7 @@ import (
 )
 
 //ftl:export
-var topic = ftl.Topic[PubSubEvent]("test_topic")
+var TestTopic = ftl.Topic[PubSubEvent]("test_topic")
 
 type PubSubEvent struct {
 	Time time.Time
@@ -21,7 +21,7 @@ func PublishTen(ctx context.Context) error {
 	for i := 0; i < 10; i++ {
 		t := time.Now()
 		logger.Infof("Publishing %v", t)
-		err := topic.Publish(ctx, PubSubEvent{Time: t})
+		err := TestTopic.Publish(ctx, PubSubEvent{Time: t})
 		if err != nil {
 			return err
 		}
@@ -34,16 +34,16 @@ func PublishOne(ctx context.Context) error {
 	logger := ftl.LoggerFromContext(ctx)
 	t := time.Now()
 	logger.Infof("Publishing %v", t)
-	return topic.Publish(ctx, PubSubEvent{Time: t})
+	return TestTopic.Publish(ctx, PubSubEvent{Time: t})
 }
 
 //ftl:export
-var topic2 = ftl.Topic[PubSubEvent]("topic2")
+var Topic2 = ftl.Topic[PubSubEvent]("topic_2")
 
 //ftl:verb
 func PublishOneToTopic2(ctx context.Context) error {
 	logger := ftl.LoggerFromContext(ctx)
 	t := time.Now()
-	logger.Infof("Publishing to topic2 %v", t)
-	return topic2.Publish(ctx, PubSubEvent{Time: t})
+	logger.Infof("Publishing to topic_2 %v", t)
+	return Topic2.Publish(ctx, PubSubEvent{Time: t})
 }

backend/controller/pubsub/testdata/go/subscriber/subscriber.go

@@ -9,7 +9,7 @@ import (
 	"github.com/TBD54566975/ftl/go-runtime/ftl" // Import the FTL SDK.
 )
 
-var _ = ftl.Subscription(publisher.Test_topic, "test_subscription")
+var _ = ftl.Subscription(publisher.TestTopic, "test_subscription")
 
 //ftl:verb
 //ftl:subscribe test_subscription
@@ -30,6 +30,6 @@ func ConsumeButFailAndRetry(ctx context.Context, req publisher.PubSubEvent) erro
 //ftl:verb
 func PublishToExternalModule(ctx context.Context) error {
 	// Get around compile-time checks
-	var topic = publisher.Test_topic
+	var topic = publisher.TestTopic
 	return topic.Publish(ctx, publisher.PubSubEvent{Time: time.Now()})
 }

backend/schema/strcase/case.go

@@ -33,6 +33,18 @@ func ToUpperCamel(s string) string {
 	return strings.Join(parts, "")
 }
 
+func ToUpperStrippedCamel(s string) string {
+	parts := split(s)
+	out := make([]string, 0, len(parts)*2)
+	for i := range parts {
+		if parts[i] == "-" || parts[i] == "_" {
+			continue
+		}
+		out = append(out, title(parts[i]))
+	}
+	return strings.Join(out, "")
+}
+
 func ToLowerSnake(s string) string {
 	parts := split(s)
 	out := make([]string, 0, len(parts)*2)

backend/schema/strcase/case_test.go

@@ -86,6 +86,34 @@ func TestUpperCamelCase(t *testing.T) {
 	}
 }
 
+func TestUpperStrippedCamel(t *testing.T) {
+	for _, tt := range []struct {
+		input    string
+		expected string
+	}{
+		{"lowercase", "Lowercase"},
+		{"Class", "Class"},
+		{"MyClass", "MyClass"},
+		{"MyC", "MyC"},
+		{"HTML", "Html"},
+		{"PDFLoader", "PdfLoader"},
+		{"AString", "AString"},
+		{"SimpleXMLParser", "SimpleXmlParser"},
+		{"vimRPCPlugin", "VimRpcPlugin"},
+		{"GL11Version", "Gl11Version"},
+		{"99Bottles", "99Bottles"},
+		{"May5", "May5"},
+		{"BFG9000", "Bfg9000"},
+		{"BöseÜberraschung", "BöseÜberraschung"},
+		{"snake_case", "SnakeCase"},
+		{"snake_Case_Caps", "SnakeCaseCaps"},
+		{"kebab-numbers99", "KebabNumbers99"},
+	} {
+		actual := ToUpperStrippedCamel(tt.input)
+		assert.Equal(t, tt.expected, actual, "UpperStrippedCamel(%q) = %v; want %v", tt.input, actual, tt.expected)
+	}
+}
+
 func TestLowerSnake(t *testing.T) {
 	for _, tt := range []struct {
 		input    string

cmd/ftl/cmd_new.go

@@ -168,6 +168,7 @@ var scaffoldFuncs = template.FuncMap{
 	"screamingSnake": strcase.ToUpperSnake,
 	"camel":          strcase.ToUpperCamel,
 	"lowerCamel":     strcase.ToLowerCamel,
+	"strippedCamel":  strcase.ToUpperStrippedCamel,
 	"kebab":          strcase.ToLowerKebab,
 	"screamingKebab": strcase.ToUpperKebab,
 	"upper":          strings.ToUpper,

docs/content/docs/reference/pubsub.md

@@ -18,13 +18,13 @@ FTL has first-class support for PubSub, modelled on the concepts of topics (wher
 First, declare a new topic:
 
 ```go
-var invoicesTopic = ftl.Topic[Invoice]("invoices")
+var Invoices = ftl.Topic[Invoice]("invoices")
 ```
 
 Then declare each subscription on the topic:
 
 ```go
-var _ = ftl.Subscription(invoicesTopic, "emailInvoices")
+var _ = ftl.Subscription(Invoices, "emailInvoices")
 ```
 
 And finally define a Sink to consume from the subscription:
@@ -39,7 +39,7 @@ func SendInvoiceEmail(ctx context.Context, in Invoice) error {
 Events can be published to a topic like so:
 
 ```go
-invoicesTopic.Publish(ctx, Invoice{...})
+Invoices.Publish(ctx, Invoice{...})
 ```
 
 > **NOTE!**

go-runtime/compile/external-module-template/.ftl/go/modules/{{ .Module.Name }}/external_module.go.tmpl

@@ -23,7 +23,7 @@ var _ = context.Background
 //
 {{- end}}
 {{- if is "Topic" .}}
-var {{.Name|title}} = ftl.Topic[{{type $.Module .Event}}]("{{.Name}}")
+var {{.Name|strippedCamel}} = ftl.Topic[{{type $.Module .Event}}]("{{.Name}}")
 {{- else if and (is "Enum" .) .IsValueEnum}}
 {{- $enumName := .Name}}
 //ftl:enum

go-runtime/compile/schema_test.go

@@ -404,10 +404,10 @@ func TestExtractModulePubSub(t *testing.T) {
 	actual := schema.Normalise(r.Module)
 	expected := `module pubsub {
 		topic payins pubsub.PayinEvent
-		// publicBroadcast is a topic that broadcasts payin events to the public.
+		// public_broadcast is a topic that broadcasts payin events to the public.
 		// out of order with subscription registration to test ordering doesn't matter.
-		export topic publicBroadcast pubsub.PayinEvent
-		subscription broadcastSubscription pubsub.publicBroadcast
+		export topic public_broadcast pubsub.PayinEvent
+		subscription broadcastSubscription pubsub.public_broadcast
 		subscription paymentProcessing pubsub.payins
 
         export data PayinEvent {
@@ -439,7 +439,7 @@ func TestExtractModuleSubscriber(t *testing.T) {
 	assert.Equal(t, nil, r.Errors, "expected no schema errors")
 	actual := schema.Normalise(r.Module)
 	expected := `module subscriber {
-		subscription subscriptionToExternalTopic pubsub.publicBroadcast
+		subscription subscriptionToExternalTopic pubsub.public_broadcast
 
         verb consumesSubscriptionFromExternalTopic(pubsub.PayinEvent) Unit
 		+subscribe subscriptionToExternalTopic

go-runtime/compile/testdata/pubsub/pubsub.go

@@ -13,7 +13,7 @@ type PayinEvent struct {
 
 //ftl:verb
 func Payin(ctx context.Context) error {
-	if err := payinsVar.Publish(ctx, PayinEvent{Name: "Test"}); err != nil {
+	if err := Payins.Publish(ctx, PayinEvent{Name: "Test"}); err != nil {
 		return fmt.Errorf("failed to publish event: %w", err)
 	}
 	return nil
@@ -26,21 +26,21 @@ func ProcessPayin(ctx context.Context, event PayinEvent) error {
 	return nil
 }
 
-var _ = ftl.Subscription(payinsVar, "paymentProcessing")
+var _ = ftl.Subscription(Payins, "paymentProcessing")
 
-var payinsVar = ftl.Topic[PayinEvent]("payins")
+var Payins = ftl.Topic[PayinEvent]("payins")
 
-var _ = ftl.Subscription(broadcast, "broadcastSubscription")
+var _ = ftl.Subscription(PublicBroadcast, "broadcastSubscription")
 
-// publicBroadcast is a topic that broadcasts payin events to the public.
+// public_broadcast is a topic that broadcasts payin events to the public.
 // out of order with subscription registration to test ordering doesn't matter.
 //
 //ftl:export
-var broadcast = ftl.Topic[PayinEvent]("publicBroadcast")
+var PublicBroadcast = ftl.Topic[PayinEvent]("public_broadcast")
 
 //ftl:verb export
 func Broadcast(ctx context.Context) error {
-	if err := broadcast.Publish(ctx, PayinEvent{Name: "Broadcast"}); err != nil {
+	if err := PublicBroadcast.Publish(ctx, PayinEvent{Name: "Broadcast"}); err != nil {
 		return fmt.Errorf("failed to publish broadcast event: %w", err)
 	}
 	return nil

go-runtime/ftl/ftltest/testdata/go/pubsub/pubsub.go

@@ -10,8 +10,8 @@ import (
 )
 
 //ftl:export
-var topic = ftl.Topic[Event]("topic")
-var subscription = ftl.Subscription(topic, "subscription")
+var Topic = ftl.Topic[Event]("topic")
+var subscription = ftl.Subscription(Topic, "subscription")
 
 //ftl:data
 type Event struct {
@@ -20,7 +20,7 @@ type Event struct {
 
 //ftl:verb
 func PublishToTopicOne(ctx context.Context, event Event) error {
-	return topic.Publish(ctx, event)
+	return Topic.Publish(ctx, event)
 }
 
 //ftl:subscribe subscription

go-runtime/ftl/ftltest/testdata/go/pubsub/pubsub_test.go

@@ -23,7 +23,7 @@ func TestSubscriberReturningErrors(t *testing.T) {
 	}
 	ftltest.WaitForSubscriptionsToComplete(ctx)
 	assert.Equal(t, count, len(ftltest.ErrorsForSubscription(ctx, subscription)))
-	assert.Equal(t, count, len(ftltest.EventsForTopic(ctx, topic)))
+	assert.Equal(t, count, len(ftltest.EventsForTopic(ctx, Topic)))
 }
 
 func TestMultipleMultipleFakeSubscribers(t *testing.T) {
@@ -50,6 +50,6 @@ func TestMultipleMultipleFakeSubscribers(t *testing.T) {
 	}
 	ftltest.WaitForSubscriptionsToComplete(ctx)
 	assert.Equal(t, 0, len(ftltest.ErrorsForSubscription(ctx, subscription)))
-	assert.Equal(t, count, len(ftltest.EventsForTopic(ctx, topic)))
+	assert.Equal(t, count, len(ftltest.EventsForTopic(ctx, Topic)))
 	assert.Equal(t, count, counter.Load())
 }

go-runtime/schema/subscription/analyzer.go

@@ -3,9 +3,9 @@ package subscription
 import (
 	"go/ast"
 	"go/types"
-	"strings"
 
 	"github.com/TBD54566975/ftl/backend/schema"
+	"github.com/TBD54566975/ftl/backend/schema/strcase"
 	"github.com/TBD54566975/ftl/go-runtime/schema/common"
 	"github.com/TBD54566975/golang-tools/go/analysis"
 	"github.com/TBD54566975/golang-tools/go/analysis/passes/inspect"
@@ -91,10 +91,7 @@ func extractSubscription(pass *analysis.Pass, obj types.Object, node *ast.CallEx
 			common.Errorf(pass, node, "subscription registration must have a topic")
 			return optional.None[*schema.Subscription]()
 		}
-		name := strings.ToLower(string(varName[0]))
-		if len(varName) > 1 {
-			name += varName[1:]
-		}
+		name := strcase.ToLowerSnake(varName)
 		topicRef = &schema.Ref{
 			Module: moduleIdent.Name,
 			Name:   name,

go-runtime/schema/topic/analyzer.go

@@ -5,6 +5,7 @@ import (
 	"go/types"
 
 	"github.com/TBD54566975/ftl/backend/schema"
+	"github.com/TBD54566975/ftl/backend/schema/strcase"
 	"github.com/TBD54566975/ftl/go-runtime/schema/common"
 	"github.com/TBD54566975/golang-tools/go/analysis"
 	"github.com/TBD54566975/golang-tools/go/analysis/passes/inspect"
@@ -47,7 +48,7 @@ func Extract(pass *analysis.Pass) (interface{}, error) {
 	return common.NewExtractorResult(pass), nil
 }
 
-// expects: _ = ftl.Topic[EventType]("name_literal")
+// expects: var NameLiteral = ftl.Topic[EventType]("name_literal")
 func extractTopic(pass *analysis.Pass, node *ast.GenDecl, callExpr *ast.CallExpr, obj types.Object) optional.Option[*schema.Topic] {
 	indexExpr, ok := callExpr.Fun.(*ast.IndexExpr)
 	if !ok {
@@ -60,9 +61,27 @@ func extractTopic(pass *analysis.Pass, node *ast.GenDecl, callExpr *ast.CallExpr
 		return optional.None[*schema.Topic]()
 	}
 
+	topicName := common.ExtractStringLiteralArg(pass, callExpr, 0)
+	expTopicName := strcase.ToLowerSnake(topicName)
+	if topicName != expTopicName {
+		common.Errorf(pass, node, "unsupported topic name %q, did you mean to use %q?", topicName, expTopicName)
+		return optional.None[*schema.Topic]()
+	}
+
+	if len(node.Specs) > 0 {
+		if t, ok := node.Specs[0].(*ast.ValueSpec); ok {
+			varName := t.Names[0].Name
+			expVarName := strcase.ToUpperStrippedCamel(topicName)
+			if varName != expVarName {
+				common.Errorf(pass, node, "unexpected topic variable name %q, did you mean %q?", varName, expVarName)
+				return optional.None[*schema.Topic]()
+			}
+		}
+	}
+
 	topic := &schema.Topic{
 		Pos:   common.GoPosToSchemaPos(pass.Fset, node.Pos()),
-		Name:  common.ExtractStringLiteralArg(pass, callExpr, 0),
+		Name:  topicName,
 		Event: typeParamType,
 	}
 	common.ApplyMetadata[*schema.Subscription](pass, obj, func(md *common.ExtractedMetadata) {

internal/scaffold.go

@@ -30,6 +30,7 @@ var scaffoldFuncs = scaffolder.FuncMap{
 	"screamingSnake": strcase.ToUpperSnake,
 	"camel":          strcase.ToUpperCamel,
 	"lowerCamel":     strcase.ToLowerCamel,
+	"strippedCamel":  strcase.ToUpperStrippedCamel,
 	"kebab":          strcase.ToLowerKebab,
 	"screamingKebab": strcase.ToUpperKebab,
 	"upper":          strings.ToUpper,

lsp/markdown/completion/pubSubTopic.md

@@ -1,7 +1,7 @@
 Declare a PubSub topic.
 
 ```go
-var invoicesTopic = ftl.Topic[Invoice]("invoices")
+var Invoices = ftl.Topic[Invoice]("invoices")
 ```
 
 See https://tbd54566975.github.io/ftl/docs/reference/pubsub/