tfprotov5+tfprotov6: Make FunctionServer implementation optional

Reference: #353

.changes/unreleased/FEATURES-20231026-164300.yaml

@@ -1,6 +1,6 @@
 kind: FEATURES
-body: 'tfprotov5: Upgraded protocol to 5.5, which implements support for provider
-  defined functions'
+body: 'tfprotov5+tfprotov6: Upgraded protocols and added types to support
+  provider-defined functions'
 time: 2023-10-26T16:43:00.024481-04:00
 custom:
   Issue: "351"

.changes/unreleased/NOTES-20231026-164359.yaml

@@ -1,7 +1,6 @@
 kind: NOTES
-body: 'all: If using terraform-plugin-framework, terraform-plugin-mux, or terraform-plugin-sdk,
-  only upgrade this Go module as part of upgrading those Go modules or you may receive
-  a `missing method CallFunction` or `missing method GetFunctions` error when compiling'
+body: 'tfprotov5+tfprotov6: An upcoming release will require the FunctionServer
+  implementation as part of ProviderServer.'
 time: 2023-10-26T16:43:59.845786-04:00
 custom:
   Issue: "351"

tfprotov5/provider.go

@@ -53,7 +53,10 @@ type ProviderServer interface {
 	// are a handy interface for defining what a function is to
 	// terraform-plugin-go, so they are their own interface that is composed
 	// into ProviderServer.
-	FunctionServer
+	//
+	// This will be required in an upcoming release.
+	// Reference: https://github.com/hashicorp/terraform-plugin-go/issues/353
+	// FunctionServer
 }
 
 // GetMetadataRequest represents a GetMetadata RPC request.

tfprotov5/tf5server/server.go

@@ -912,6 +912,28 @@ func (s *server) CallFunction(ctx context.Context, protoReq *tfplugin5.CallFunct
 	logging.ProtocolTrace(ctx, "Received request")
 	defer logging.ProtocolTrace(ctx, "Served request")
 
+	// Remove this check and error in preference of s.downstream.CallFunction
+	// below once ProviderServer interface requires FunctionServer.
+	// Reference: https://github.com/hashicorp/terraform-plugin-go/issues/353
+	functionServer, ok := s.downstream.(tfprotov5.FunctionServer)
+
+	if !ok {
+		logging.ProtocolError(ctx, "ProviderServer does not implement FunctionServer")
+
+		protoResp := &tfplugin5.CallFunction_Response{
+			Diagnostics: []*tfplugin5.Diagnostic{
+				{
+					Severity: tfplugin5.Diagnostic_ERROR,
+					Summary:  "Provider Functions Not Implemented",
+					Detail: "A provider-defined function call was received by the provider, however the provider does not implement functions. " +
+						"Either upgrade the provider to a version that implements provider-defined functions or this is a bug in Terraform that should be reported to the Terraform maintainers.",
+				},
+			},
+		}
+
+		return protoResp, nil
+	}
+
 	req, err := fromproto.CallFunctionRequest(protoReq)
 
 	if err != nil {
@@ -926,7 +948,9 @@ func (s *server) CallFunction(ctx context.Context, protoReq *tfplugin5.CallFunct
 
 	ctx = tf5serverlogging.DownstreamRequest(ctx)
 
-	resp, err := s.downstream.CallFunction(ctx, req)
+	// Reference: https://github.com/hashicorp/terraform-plugin-go/issues/353
+	// resp, err := s.downstream.CallFunction(ctx, req)
+	resp, err := functionServer.CallFunction(ctx, req)
 
 	if err != nil {
 		logging.ProtocolError(ctx, "Error from downstream", map[string]any{logging.KeyError: err})
@@ -954,6 +978,21 @@ func (s *server) GetFunctions(ctx context.Context, protoReq *tfplugin5.GetFuncti
 	logging.ProtocolTrace(ctx, "Received request")
 	defer logging.ProtocolTrace(ctx, "Served request")
 
+	// Remove this check and response in preference of s.downstream.GetFunctions
+	// below once ProviderServer interface requires FunctionServer.
+	// Reference: https://github.com/hashicorp/terraform-plugin-go/issues/353
+	functionServer, ok := s.downstream.(tfprotov5.FunctionServer)
+
+	if !ok {
+		logging.ProtocolWarn(ctx, "ProviderServer does not implement FunctionServer")
+
+		protoResp := &tfplugin5.GetFunctions_Response{
+			Functions: map[string]*tfplugin5.Function{},
+		}
+
+		return protoResp, nil
+	}
+
 	req, err := fromproto.GetFunctionsRequest(protoReq)
 
 	if err != nil {
@@ -964,7 +1003,9 @@ func (s *server) GetFunctions(ctx context.Context, protoReq *tfplugin5.GetFuncti
 
 	ctx = tf5serverlogging.DownstreamRequest(ctx)
 
-	resp, err := s.downstream.GetFunctions(ctx, req)
+	// Reference: https://github.com/hashicorp/terraform-plugin-go/issues/353
+	// resp, err := s.downstream.GetFunctions(ctx, req)
+	resp, err := functionServer.GetFunctions(ctx, req)
 
 	if err != nil {
 		logging.ProtocolError(ctx, "Error from downstream", map[string]any{logging.KeyError: err})

tfprotov6/provider.go

@@ -53,7 +53,10 @@ type ProviderServer interface {
 	// are a handy interface for defining what a function is to
 	// terraform-plugin-go, so they are their own interface that is composed
 	// into ProviderServer.
-	FunctionServer
+	//
+	// This will be required in an upcoming release.
+	// Reference: https://github.com/hashicorp/terraform-plugin-go/issues/353
+	// FunctionServer
 }
 
 // GetMetadataRequest represents a GetMetadata RPC request.

tfprotov6/tf6server/server.go

@@ -910,6 +910,28 @@ func (s *server) CallFunction(ctx context.Context, protoReq *tfplugin6.CallFunct
 	logging.ProtocolTrace(ctx, "Received request")
 	defer logging.ProtocolTrace(ctx, "Served request")
 
+	// Remove this check and error in preference of s.downstream.CallFunction
+	// below once ProviderServer interface requires FunctionServer.
+	// Reference: https://github.com/hashicorp/terraform-plugin-go/issues/353
+	functionServer, ok := s.downstream.(tfprotov6.FunctionServer)
+
+	if !ok {
+		logging.ProtocolError(ctx, "ProviderServer does not implement FunctionServer")
+
+		protoResp := &tfplugin6.CallFunction_Response{
+			Diagnostics: []*tfplugin6.Diagnostic{
+				{
+					Severity: tfplugin6.Diagnostic_ERROR,
+					Summary:  "Provider Functions Not Implemented",
+					Detail: "A provider-defined function call was received by the provider, however the provider does not implement functions. " +
+						"Either upgrade the provider to a version that implements provider-defined functions or this is a bug in Terraform that should be reported to the Terraform maintainers.",
+				},
+			},
+		}
+
+		return protoResp, nil
+	}
+
 	req, err := fromproto.CallFunctionRequest(protoReq)
 
 	if err != nil {
@@ -924,7 +946,9 @@ func (s *server) CallFunction(ctx context.Context, protoReq *tfplugin6.CallFunct
 
 	ctx = tf6serverlogging.DownstreamRequest(ctx)
 
-	resp, err := s.downstream.CallFunction(ctx, req)
+	// Reference: https://github.com/hashicorp/terraform-plugin-go/issues/353
+	// resp, err := s.downstream.CallFunction(ctx, req)
+	resp, err := functionServer.CallFunction(ctx, req)
 
 	if err != nil {
 		logging.ProtocolError(ctx, "Error from downstream", map[string]any{logging.KeyError: err})
@@ -952,6 +976,21 @@ func (s *server) GetFunctions(ctx context.Context, protoReq *tfplugin6.GetFuncti
 	logging.ProtocolTrace(ctx, "Received request")
 	defer logging.ProtocolTrace(ctx, "Served request")
 
+	// Remove this check and response in preference of s.downstream.GetFunctions
+	// below once ProviderServer interface requires FunctionServer.
+	// Reference: https://github.com/hashicorp/terraform-plugin-go/issues/353
+	functionServer, ok := s.downstream.(tfprotov6.FunctionServer)
+
+	if !ok {
+		logging.ProtocolWarn(ctx, "ProviderServer does not implement FunctionServer")
+
+		protoResp := &tfplugin6.GetFunctions_Response{
+			Functions: map[string]*tfplugin6.Function{},
+		}
+
+		return protoResp, nil
+	}
+
 	req, err := fromproto.GetFunctionsRequest(protoReq)
 
 	if err != nil {
@@ -962,7 +1001,9 @@ func (s *server) GetFunctions(ctx context.Context, protoReq *tfplugin6.GetFuncti
 
 	ctx = tf6serverlogging.DownstreamRequest(ctx)
 
-	resp, err := s.downstream.GetFunctions(ctx, req)
+	// Reference: https://github.com/hashicorp/terraform-plugin-go/issues/353
+	// resp, err := s.downstream.GetFunctions(ctx, req)
+	resp, err := functionServer.GetFunctions(ctx, req)
 
 	if err != nil {
 		logging.ProtocolError(ctx, "Error from downstream", map[string]any{logging.KeyError: err})