tftypes: Guarantee Type interface MarshalJSON error safety (#371)

Reference: #238
Reference: #365

This change removes the necessity for protocol type conversion to handle JSON encoding errors, therefore greatly simplifying those packages. Type system conversions into the protocol should always be possible, albeit potentially not valid for usage in Terraform. The protocol conversion code is not the place to handle that consideration, rather if developers want to validate their schema/function/type definitions before its sent across the protocol with respect to the validation rules imposed by Terraform, separate validation functionality should be introduced. This is not conceptually new, does not introduce behavior changes, and uses fuzz testing to verify that a panic is not possible today in the one way that developers could potentially introduce a new panic.

The fuzz testing has been run for 60 seconds on a currently powerful workstation without generating any failure cases:

```console
$ go test -fuzz=Fuzz -fuzztime=60s ./tftypes
fuzz: elapsed: 0s, gathering baseline coverage: 0/138 completed
fuzz: elapsed: 0s, gathering baseline coverage: 138/138 completed, now fuzzing with 10 workers
fuzz: elapsed: 3s, execs: 406242 (135409/sec), new interesting: 6 (total: 144)
fuzz: elapsed: 6s, execs: 833268 (142312/sec), new interesting: 7 (total: 145)
fuzz: elapsed: 9s, execs: 1269960 (145562/sec), new interesting: 7 (total: 145)
fuzz: elapsed: 12s, execs: 1684371 (138143/sec), new interesting: 8 (total: 146)
fuzz: elapsed: 15s, execs: 2137768 (151160/sec), new interesting: 9 (total: 147)
fuzz: elapsed: 18s, execs: 2574729 (145641/sec), new interesting: 11 (total: 149)
fuzz: elapsed: 21s, execs: 3011973 (145722/sec), new interesting: 12 (total: 150)
fuzz: elapsed: 24s, execs: 3442147 (143418/sec), new interesting: 12 (total: 150)
fuzz: elapsed: 27s, execs: 3868833 (142210/sec), new interesting: 12 (total: 150)
fuzz: elapsed: 30s, execs: 4313780 (148320/sec), new interesting: 14 (total: 152)
fuzz: elapsed: 33s, execs: 4763813 (150034/sec), new interesting: 14 (total: 152)
fuzz: elapsed: 36s, execs: 5201686 (145936/sec), new interesting: 15 (total: 153)
fuzz: elapsed: 39s, execs: 5613562 (137285/sec), new interesting: 15 (total: 153)
fuzz: elapsed: 42s, execs: 6051164 (145875/sec), new interesting: 15 (total: 153)
fuzz: elapsed: 45s, execs: 6485230 (144677/sec), new interesting: 15 (total: 153)
fuzz: elapsed: 48s, execs: 6912045 (142294/sec), new interesting: 15 (total: 153)
fuzz: elapsed: 51s, execs: 7349416 (145756/sec), new interesting: 16 (total: 154)
fuzz: elapsed: 54s, execs: 7792201 (147626/sec), new interesting: 16 (total: 154)
fuzz: elapsed: 57s, execs: 8225683 (144471/sec), new interesting: 18 (total: 156)
fuzz: elapsed: 1m0s, execs: 8637257 (137227/sec), new interesting: 18 (total: 156)
fuzz: elapsed: 1m0s, execs: 8637257 (0/sec), new interesting: 18 (total: 156)
PASS
ok      github.com/hashicorp/terraform-plugin-go/tftypes        60.883s
```

Author: bflad

tfprotov5/internal/toproto/dynamic_value.go

@@ -4,8 +4,6 @@
 package toproto
 
 import (
-	"fmt"
-
 	"github.com/hashicorp/terraform-plugin-go/tfprotov5"
 	"github.com/hashicorp/terraform-plugin-go/tfprotov5/internal/tfplugin5"
 	"github.com/hashicorp/terraform-plugin-go/tftypes"
@@ -24,17 +22,14 @@ func DynamicValue(in *tfprotov5.DynamicValue) *tfplugin5.DynamicValue {
 	return resp
 }
 
-func CtyType(in tftypes.Type) ([]byte, error) {
+func CtyType(in tftypes.Type) []byte {
 	if in == nil {
-		return nil, nil
+		return nil
 	}
 
-	switch {
-	case in.Is(tftypes.String), in.Is(tftypes.Bool), in.Is(tftypes.Number),
-		in.Is(tftypes.List{}), in.Is(tftypes.Map{}),
-		in.Is(tftypes.Set{}), in.Is(tftypes.Object{}),
-		in.Is(tftypes.Tuple{}), in.Is(tftypes.DynamicPseudoType):
-		return in.MarshalJSON() //nolint:staticcheck
-	}
-	return nil, fmt.Errorf("unknown type %s", in)
+	// MarshalJSON is always error safe.
+	// nolint:staticcheck // Intended first-party usage
+	resp, _ := in.MarshalJSON()
+
+	return resp
 }

tfprotov5/internal/toproto/function.go

@@ -4,8 +4,6 @@
 package toproto
 
 import (
-	"fmt"
-
 	"github.com/hashicorp/terraform-plugin-go/tfprotov5"
 	"github.com/hashicorp/terraform-plugin-go/tfprotov5/internal/tfplugin5"
 )
@@ -23,61 +21,31 @@ func CallFunction_Response(in *tfprotov5.CallFunctionResponse) *tfplugin5.CallFu
 	return resp
 }
 
-func Function(in *tfprotov5.Function) (*tfplugin5.Function, error) {
+func Function(in *tfprotov5.Function) *tfplugin5.Function {
 	if in == nil {
-		return nil, nil
+		return nil
 	}
 
 	resp := &tfplugin5.Function{
 		Description:        in.Description,
 		DescriptionKind:    StringKind(in.DescriptionKind),
 		DeprecationMessage: in.DeprecationMessage,
 		Parameters:         make([]*tfplugin5.Function_Parameter, 0, len(in.Parameters)),
+		Return:             Function_Return(in.Return),
 		Summary:            in.Summary,
+		VariadicParameter:  Function_Parameter(in.VariadicParameter),
 	}
 
-	for position, parameter := range in.Parameters {
-		if parameter == nil {
-			return nil, fmt.Errorf("missing function parameter definition at position: %d", position)
-		}
-
-		functionParameter, err := Function_Parameter(parameter)
-
-		if err != nil {
-			return nil, fmt.Errorf("unable to marshal function parameter at position %d: %w", position, err)
-		}
-
-		resp.Parameters = append(resp.Parameters, functionParameter)
-	}
-
-	if in.Return == nil {
-		return nil, fmt.Errorf("missing function return definition")
-	}
-
-	functionReturn, err := Function_Return(in.Return)
-
-	if err != nil {
-		return nil, fmt.Errorf("unable to marshal function return: %w", err)
+	for _, parameter := range in.Parameters {
+		resp.Parameters = append(resp.Parameters, Function_Parameter(parameter))
 	}
 
-	resp.Return = functionReturn
-
-	if in.VariadicParameter != nil {
-		variadicParameter, err := Function_Parameter(in.VariadicParameter)
-
-		if err != nil {
-			return nil, fmt.Errorf("unable to marshal variadic function parameter: %w", err)
-		}
-
-		resp.VariadicParameter = variadicParameter
-	}
-
-	return resp, nil
+	return resp
 }
 
-func Function_Parameter(in *tfprotov5.FunctionParameter) (*tfplugin5.Function_Parameter, error) {
+func Function_Parameter(in *tfprotov5.FunctionParameter) *tfplugin5.Function_Parameter {
 	if in == nil {
-		return nil, nil
+		return nil
 	}
 
 	resp := &tfplugin5.Function_Parameter{
@@ -86,66 +54,39 @@ func Function_Parameter(in *tfprotov5.FunctionParameter) (*tfplugin5.Function_Pa
 		Description:        in.Description,
 		DescriptionKind:    StringKind(in.DescriptionKind),
 		Name:               in.Name,
+		Type:               CtyType(in.Type),
 	}
 
-	if in.Type == nil {
-		return nil, fmt.Errorf("missing function parameter type definition")
-	}
-
-	ctyType, err := CtyType(in.Type)
-
-	if err != nil {
-		return resp, fmt.Errorf("error marshaling function parameter type: %w", err)
-	}
-
-	resp.Type = ctyType
-
-	return resp, nil
+	return resp
 }
 
-func Function_Return(in *tfprotov5.FunctionReturn) (*tfplugin5.Function_Return, error) {
+func Function_Return(in *tfprotov5.FunctionReturn) *tfplugin5.Function_Return {
 	if in == nil {
-		return nil, nil
-	}
-
-	resp := &tfplugin5.Function_Return{}
-
-	if in.Type == nil {
-		return nil, fmt.Errorf("missing function return type definition")
+		return nil
 	}
 
-	ctyType, err := CtyType(in.Type)
-
-	if err != nil {
-		return resp, fmt.Errorf("error marshaling function return type: %w", err)
+	resp := &tfplugin5.Function_Return{
+		Type: CtyType(in.Type),
 	}
 
-	resp.Type = ctyType
-
-	return resp, nil
+	return resp
 }
 
-func GetFunctions_Response(in *tfprotov5.GetFunctionsResponse) (*tfplugin5.GetFunctions_Response, error) {
+func GetFunctions_Response(in *tfprotov5.GetFunctionsResponse) *tfplugin5.GetFunctions_Response {
 	if in == nil {
-		return nil, nil
+		return nil
 	}
 
 	resp := &tfplugin5.GetFunctions_Response{
 		Diagnostics: Diagnostics(in.Diagnostics),
 		Functions:   make(map[string]*tfplugin5.Function, len(in.Functions)),
 	}
 
-	for name, functionPtr := range in.Functions {
-		function, err := Function(functionPtr)
-
-		if err != nil {
-			return nil, fmt.Errorf("error marshaling function definition for %q: %w", name, err)
-		}
-
-		resp.Functions[name] = function
+	for name, function := range in.Functions {
+		resp.Functions[name] = Function(function)
 	}
 
-	return resp, nil
+	return resp
 }
 
 func GetMetadata_FunctionMetadata(in *tfprotov5.FunctionMetadata) *tfplugin5.GetMetadata_FunctionMetadata {