go: fix declaring multiple gateways

v2/app/errors.go

@@ -46,4 +46,10 @@ var (
 		"Conflicting service definitions",
 		"A service cannot use both an //encore:service directive and a service.New() call.",
 	)
+
+	errExposeUnknownGateway = errRange.Newf(
+		"Endpoint exposed on undeclared gateway",
+		"The endpoint is exposed on gateway %q via //encore:expose, but no gateway with that name has been declared.",
+		errors.WithDetails("Add gateway.New(\"<name>\", gateway.Config{}) in an encore.gateway.go file. The implicit \"api-gateway\" name is only available when no gateways are declared at all."),
+	)
 )

v2/app/testdata/expose_unknown_gateway.txt

@@ -0,0 +1,50 @@
+# Verify that //encore:expose with a gateway name that hasn't been declared
+# (and isn't the synthesized "api-gateway" default) is rejected.
+! parse
+err 'exposed on undeclared gateway'
+
+-- encore.app --
+{"edition": "2026"}
+
+-- gw/encore.gateway.go --
+package gw
+
+import "encore.dev/gateway"
+
+var _ = gateway.New("api", gateway.Config{})
+
+-- svc/encore.service.go --
+package svc
+
+import "encore.dev/service"
+
+type MyService struct{}
+
+var _ = service.New("svc", service.Config[MyService]{})
+
+-- svc/svc.go --
+package svc
+
+import "context"
+
+//encore:api path=/hello
+//encore:expose gateway=does-not-exist
+func Hello(ctx context.Context) error { return nil }
+-- want: errors --
+
+── Endpoint exposed on undeclared gateway ─────────────────────────────────────────────────[E9999]──
+
+The endpoint is exposed on gateway "does-not-exist" via //encore:expose, but no gateway with that
+name has been declared.
+
+   ╭─[ svc/svc.go:6:17 ]
+   │
+ 4 │
+ 5 │ //encore:api path=/hello
+ 6 │ //encore:expose gateway=does-not-exist
+   ⋮                 ──────────────────────
+ 7 │ func Hello(ctx context.Context) error { return nil }
+───╯
+
+Add gateway.New("<name>", gateway.Config{}) in an encore.gateway.go file. The implicit
+"api-gateway" name is only available when no gateways are declared at all.

v2/app/testdata/expose_user_named_gateway.txt

@@ -0,0 +1,32 @@
+# Verify that a user-declared gateway with a non-default name works end-to-end:
+# the endpoint's expose list should reference the user's gateway, and the
+# implicit "api-gateway" should NOT be synthesized when any gateway is declared.
+parse
+
+-- encore.app --
+{"edition": "2026"}
+
+-- gw/encore.gateway.go --
+package gw
+
+import "encore.dev/gateway"
+
+var _ = gateway.New("api", gateway.Config{})
+
+-- svc/encore.service.go --
+package svc
+
+import "encore.dev/service"
+
+type MyService struct{}
+
+var _ = service.New("svc", service.Config[MyService]{})
+
+-- svc/svc.go --
+package svc
+
+import "context"
+
+//encore:api path=/hello
+//encore:expose gateway=api
+func Hello(ctx context.Context) error { return nil }

v2/app/v2meta/v2meta.go

@@ -10,8 +10,8 @@ import (
 
 	metav2 "encore.dev/appruntime/exported/proto/encore/parser/meta/v2"
 	schemapb "encore.dev/appruntime/exported/proto/encore/parser/schema/v2"
-	"encr.dev/pkg/fns"
 	sourcev1 "encore.dev/appruntime/exported/proto/encore/parser/source/v1"
+	"encr.dev/pkg/fns"
 	"encr.dev/pkg/idents"
 	"encr.dev/pkg/option"
 	"encr.dev/v2/app"
@@ -543,13 +543,6 @@ func (b *builder) build() {
 		}
 	}
 
-	// Ensure a default gateway exists.
-	if len(b.res.Gateways) == 0 {
-		b.res.Gateways["api-gateway"] = &metav2.Gateway{
-			RepoId: "default",
-			Name:   "api-gateway",
-		}
-	}
 	// For legacy edition (single auth handler), attach it to the first gateway.
 	// For edition 2026 with multiple handlers, gateways get their handler from
 	// the gateway.New() config (already parsed). For now, attach the first handler
@@ -1321,7 +1314,6 @@ func (b *builder) secrets(r *secrets.Secrets) {
 	}
 }
 
-
 func (b *builder) apiPath(path *resourcepaths.Path) *metav2.Path {
 	res := &metav2.Path{}
 	for _, p := range path.Segments {

v2/app/validate_apis.go

@@ -23,6 +23,13 @@ func (d *Desc) validateAPIs(pc *parsectx.Context, fw *apiframework.AppDesc, resu
 
 	apiPaths := resourcepaths.NewSet()
 
+	// Build a set of declared gateway names. discoverGateways guarantees
+	// "api-gateway" is included when no gateway has been explicitly declared.
+	declaredGateways := make(map[string]struct{}, len(d.Gateways))
+	for _, gw := range d.Gateways {
+		declaredGateways[gw.EncoreName] = struct{}{}
+	}
+
 	for _, svc := range d.Services {
 		fwSvc, ok := svc.Framework.Get()
 		if !ok {
@@ -43,6 +50,17 @@ func (d *Desc) validateAPIs(pc *parsectx.Context, fw *apiframework.AppDesc, resu
 				)
 			}
 
+			// Verify each gateway named in //encore:expose has been declared
+			// (or matches the synthesized default). Only edition 2026 endpoints
+			// can populate ExposedGateways; legacy endpoints leave it empty.
+			for _, name := range ep.ExposedGateways {
+				if _, ok := declaredGateways[name]; ok {
+					continue
+				}
+				err := errExposeUnknownGateway(name)
+				pc.Errs.Add(errors.AtOptionalNode(err, ep.ExposeField))
+			}
+
 			// Check for duplicate paths by adding them to the set
 			// Note, errors will be reported automatically to pc.Errs
 			for _, method := range ep.HTTPMethods {

v2/codegenv2/servergen/servergen.go

@@ -11,6 +11,8 @@ import (
 
 	"github.com/dave/jennifer/jen"
 
+	metav2 "encore.dev/appruntime/exported/proto/encore/parser/meta/v2"
+	schemapb "encore.dev/appruntime/exported/proto/encore/parser/schema/v2"
 	"encr.dev/pkg/paths"
 	"encr.dev/v2/app"
 	"encr.dev/v2/app/apiframework"
@@ -20,8 +22,6 @@ import (
 	"encr.dev/v2/parser/apis/api"
 	"encr.dev/v2/parser/apis/selector"
 	"encr.dev/v2/parser/infra/pubsub"
-	metav2 "encore.dev/appruntime/exported/proto/encore/parser/meta/v2"
-	schemapb "encore.dev/appruntime/exported/proto/encore/parser/schema/v2"
 )
 
 const (
@@ -220,12 +220,23 @@ func genEndpoint(grpcService string, ep *api.Endpoint, handlerDecl *codegenv2.Va
 
 	// Set access-related fields.
 	switch ep.Access {
-	case api.Public:
-		d[jen.Id("NoAuthRequired")] = jen.True()
-		d[jen.Id("ExposedGateways")] = jen.Index().String().Values(jen.Lit("api-gateway"))
-	case api.Auth:
-		d[jen.Id("NoAuthRequired")] = jen.False()
-		d[jen.Id("ExposedGateways")] = jen.Index().String().Values(jen.Lit("api-gateway"))
+	case api.Public, api.Auth:
+		d[jen.Id("NoAuthRequired")] = jen.Lit(ep.Access == api.Public)
+
+		// Use the parser's expose list if populated (edition 2026 with
+		// //encore:expose gateway=...). Fall back to the synthesized
+		// "api-gateway" — discoverGateways guarantees a gateway with that
+		// name exists when no other gateway has been declared.
+		names := ep.ExposedGateways
+		if len(names) == 0 {
+			names = []string{"api-gateway"}
+		}
+		lits := make([]jen.Code, len(names))
+		for i, n := range names {
+			lits[i] = jen.Lit(n)
+		}
+		d[jen.Id("ExposedGateways")] = jen.Index().String().Values(lits...)
+
 	case api.Private:
 		d[jen.Id("NoAuthRequired")] = jen.True()
 	}