tfprotov5+tfprotov6: Initial provider defined functions implementation

Reference: hashicorp/terraform#34383

The next version of the plugin protocol (5.5/6.5) includes support for provider defined functions. This change introduces the initial implementation of that support including:

- Updated Protocol Buffers definitions
- Re-generated Protocol Buffers Go code
- Initial implementations of `tfprotov5` and `tfprotov6` package abstractions and wiring between those abstractions and the Protocol Buffers generated Go code
- Initial implementations of `tfprotov5/tf5server` and `tfprotov6/tf6server` for the new `GetFunctions` and `CallFunction` RPCs

Similar to the last set of protocol RPC changes, `ProviderServer` implementations must implement the new RPCs by either including function support or always returning an error. The HashiCorp-maintained provider development SDKs will receive updates to match this change.

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

@@ -0,0 +1,6 @@
+kind: FEATURES
+body: 'tfprotov5: Upgraded protocol to 5.5, which implements support for provider
+  defined functions'
+time: 2023-10-26T16:43:00.024481-04:00
+custom:
+  Issue: "9999"

.changes/unreleased/FEATURES-20231026-164327.yaml

@@ -0,0 +1,6 @@
+kind: FEATURES
+body: 'tfprotov6: Upgraded protocol to 6.5, which implements support for provider
+  defined functions'
+time: 2023-10-26T16:43:27.221334-04:00
+custom:
+  Issue: "9999"

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

@@ -0,0 +1,7 @@
+kind: NOTES
+body: 'all: If using terraform-plugin-framework, terraform-plugin-mux, or terraform-plugin-sdk,
+  only upgrade this Go module when upgrading those Go modules or you may receive
+  a `missing CallFunction method` or `missing GetFunctions method` error when compiling'
+time: 2023-10-26T16:43:59.845786-04:00
+custom:
+  Issue: "9999"

internal/logging/keys.go

@@ -11,6 +11,9 @@ const (
 	// Attribute of the diagnostic being logged.
 	KeyDiagnosticAttribute = "diagnostic_attribute"
 
+	// Function Argument of the diagnostic being logged.
+	KeyDiagnosticFunctionArgument = "diagnostic_function_argument"
+
 	// Number of the error diagnostics.
 	KeyDiagnosticErrorCount = "diagnostic_error_count"
 

tfprotov5/diagnostic.go

@@ -42,6 +42,10 @@ type Diagnostic struct {
 	// indicate that the problem is with a certain field in the resource,
 	// which helps users find the source of the problem.
 	Attribute *tftypes.AttributePath
+
+	// FunctionArgument is the positional function argument for aligning
+	// configuration source.
+	FunctionArgument *int64
 }
 
 // DiagnosticSeverity represents different classes of Diagnostic which affect

tfprotov5/function.go

@@ -0,0 +1,141 @@
+// Copyright (c) HashiCorp, Inc.
+// SPDX-License-Identifier: MPL-2.0
+
+package tfprotov5
+
+import (
+	"context"
+
+	"github.com/hashicorp/terraform-plugin-go/tftypes"
+)
+
+// Function describes the definition of a function. Result must be defined.
+type Function struct {
+	// Parameters is the ordered list of positional function parameters.
+	Parameters []*FunctionParameter
+
+	// VariadicParameter is an optional final parameter which accepts zero or
+	// more argument values, in which Terraform will send an ordered list of the
+	// parameter type.
+	VariadicParameter *FunctionParameter
+
+	// Return is the function result.
+	Return *FunctionReturn
+
+	// Summary is the shortened human-readable documentation for the function.
+	Summary string
+
+	// Description is the longer human-readable documentation for the function.
+	Description string
+
+	// DescriptionKind indicates the formatting and encoding that the
+	// Description field is using.
+	DescriptionKind StringKind
+
+	// DeprecationMessage is the human-readable documentation if the function
+	// is deprecated. This message should be practitioner oriented to explain
+	// how their configuration should be updated.
+	DeprecationMessage string
+}
+
+// FunctionMetadata describes metadata for a function in the GetMetadata RPC.
+type FunctionMetadata struct {
+	// Name is the name of the function.
+	Name string
+}
+
+// FunctionParameter describes the definition of a function parameter. Type must
+// be defined.
+type FunctionParameter struct {
+	// AllowNullValue when enabled denotes that a null argument value can be
+	// passed to the provider. When disabled, Terraform returns an error if the
+	// argument value is null.
+	AllowNullValue bool
+
+	// AllowUnknownValues when enabled denotes that any unknown argument value
+	// (recursively checked for collections) can be passed to the provider. When
+	// disabled and an unknown value is present, Terraform skips the function
+	// call entirely and returns an unknown value result from the function.
+	AllowUnknownValues bool
+
+	// Description is the human-readable documentation for the parameter.
+	Description string
+
+	// DescriptionKind indicates the formatting and encoding that the
+	// Description field is using.
+	DescriptionKind StringKind
+
+	// Name is the human-readable display name for the parameter. Parameters
+	// are by definition positional and this name is only used in documentation.
+	Name string
+
+	// Type indicates the type of data the parameter expects.
+	Type tftypes.Type
+}
+
+// FunctionReturn describes the definition of a function result. Type must be
+// defined.
+type FunctionReturn struct {
+	// Type indicates the type of return data.
+	Type tftypes.Type
+}
+
+// FunctionServer is an interface containing the methods a function
+// implementation needs to fill.
+type FunctionServer interface {
+	// CallFunction is called when Terraform wants to execute the logic of a
+	// function referenced in the configuration.
+	CallFunction(context.Context, *CallFunctionRequest) (*CallFunctionResponse, error)
+
+	// GetFunctions is called when Terraform wants to lookup which functions a
+	// provider supports when not calling GetProviderSchema.
+	GetFunctions(context.Context, *GetFunctionsRequest) (*GetFunctionsResponse, error)
+}
+
+// CallFunctionRequest is the request Terraform sends when it wants to execute
+// the logic of function referenced in the configuration.
+type CallFunctionRequest struct {
+	// Name is the function name being called.
+	Name string
+
+	// Arguments is the configuration value of each argument the practitioner
+	// supplied for the function call. The ordering and value of each element
+	// matches the function parameters and their associated type.  If the
+	// function definition includes a final variadic parameter, its value is an
+	// ordered list of the variadic parameter type.
+	Arguments []*DynamicValue
+}
+
+// CallFunctionResponse is the response from the provider with the result of
+// executing the logic of the function.
+type CallFunctionResponse struct {
+	// Diagnostics report errors or warnings related to the execution of the
+	// function logic. Returning an empty slice indicates a successful response
+	// with no warnings or errors presented to practitioners.
+	Diagnostics []*Diagnostic
+
+	// Result is the return value from the called function, matching the result
+	// type in the function definition.
+	Result *DynamicValue
+}
+
+// GetFunctionsRequest is the request Terraform sends when it wants to lookup
+// which functions a provider supports when not calling GetProviderSchema.
+type GetFunctionsRequest struct{}
+
+// GetFunctionsResponse is the response from the provider about the implemented
+// functions.
+type GetFunctionsResponse struct {
+	// Diagnostics report errors or warnings related to the provider
+	// implementation. Returning an empty slice indicates a successful response
+	// with no warnings or errors presented to practitioners.
+	Diagnostics []*Diagnostic
+
+	// Functions is a map of function names to their definition.
+	//
+	// Unlike data resources and managed resources, the name should NOT be
+	// prefixed with the provider name and an underscore. Configuration
+	// references to functions use a separate namespacing syntax that already
+	// includes the provider name.
+	Functions map[string]*Function
+}

tfprotov5/internal/diag/diagnostics.go

@@ -53,6 +53,10 @@ func (d Diagnostics) Log(ctx context.Context) {
 			diagnosticFields[logging.KeyDiagnosticAttribute] = diagnostic.Attribute.String()
 		}
 
+		if diagnostic.FunctionArgument != nil {
+			diagnosticFields[logging.KeyDiagnosticFunctionArgument] = *diagnostic.FunctionArgument
+		}
+
 		switch diagnostic.Severity {
 		case tfprotov5.DiagnosticSeverityError:
 			logging.ProtocolError(ctx, "Response contains error diagnostic", diagnosticFields)

tfprotov5/internal/fromproto/function.go

@@ -0,0 +1,36 @@
+// Copyright (c) HashiCorp, Inc.
+// SPDX-License-Identifier: MPL-2.0
+
+package fromproto
+
+import (
+	"github.com/hashicorp/terraform-plugin-go/tfprotov5"
+	"github.com/hashicorp/terraform-plugin-go/tfprotov5/internal/tfplugin5"
+)
+
+func CallFunctionRequest(in *tfplugin5.CallFunction_Request) (*tfprotov5.CallFunctionRequest, error) {
+	if in == nil {
+		return nil, nil
+	}
+
+	resp := &tfprotov5.CallFunctionRequest{
+		Arguments: make([]*tfprotov5.DynamicValue, 0, len(in.Arguments)),
+		Name:      in.Name,
+	}
+
+	for _, argument := range in.Arguments {
+		resp.Arguments = append(resp.Arguments, DynamicValue(argument))
+	}
+
+	return resp, nil
+}
+
+func GetFunctionsRequest(in *tfplugin5.GetFunctions_Request) (*tfprotov5.GetFunctionsRequest, error) {
+	if in == nil {
+		return nil, nil
+	}
+
+	resp := &tfprotov5.GetFunctionsRequest{}
+
+	return resp, nil
+}