fix(sdkgen/go): illegal cast in resource constructors when secret-wra…

…pping input arguments

Codegen for wrapping input properties as secrets performed an incorrect cast, as
seen in Pulumi's AWS classic SDK.

Using the sample program and the resource constructor described in #11664 as our
 test case, from `pulumi-aws/sdk/v5/go/aws/secretmanager/secretVersion.go`:

```go
      func NewSecretVersion(ctx *pulumi.Context,
        name string, args *SecretVersionArgs, opts ...pulumi.ResourceOption) (*SecretVersion, error) {
        if args == nil {
          return nil, errors.New("missing one or more required arguments")
        }

        if args.SecretId == nil {
          return nil, errors.New("invalid value for required argument 'SecretId'")
        }
        if args.SecretBinary != nil {
82:        args.SecretBinary = pulumi.ToSecret(args.SecretBinary).(pulumi.StringPtrOutput)
        }
        if args.SecretString != nil {
85:        args.SecretString = pulumi.ToSecret(args.SecretString).(pulumi.StringPtrOutput)
        }
```

`args.SecretBinary` is of type `pulumi.StringPtrInput` and `pulumi.ToSecret`
returns `pulumi.Output` returns its input as an Output-wrapped value marked
secret.

As `StringPtrInput` is an interface accepting multiple input types, the return
value would be either `pulumi.StringOutput` `pulumi.StringPtrOutput`. These are
both concrete types, and casting to the incorrect one would panic.

Fortunately we can cast back to the arg's type, as verified by building the new
codegen and testing the Pulumi program in #11664. This should handle regular
inputs and plain inputs.

The new codegen below converts an input type `T` to `pulumi.Output`, then casts
back to `T`.

```go
      func NewSecretVersion(ctx *pulumi.Context,
        // ...
        if args.SecretBinary != nil {
82:             args.SecretBinary = pulumi.ToSecret(args.SecretBinary).(pulumi.StringPtrInput)
        }
        if args.SecretString != nil {
85:             args.SecretString = pulumi.ToSecret(args.SecretString).(pulumi.StringPtrInput)
        }
```

changelog/pending/20221217--sdkgen-go--illegal-cast-in-resource-constructors-when-secret-wrapping-input-arguments.yaml

@@ -0,0 +1,4 @@
+changes:
+- type: fix
+  scope: sdkgen/go
+  description: Illegal cast in resource constructors when secret-wrapping input arguments.

pkg/codegen/go/gen.go

@@ -1763,7 +1763,8 @@ func (pkg *pkgContext) genResource(w io.Writer, r *schema.Resource, generateReso
 	// Setup secrets
 	for _, p := range secretInputProps {
 		fmt.Fprintf(w, "\tif args.%s != nil {\n", pkg.fieldName(r, p))
-		fmt.Fprintf(w, "\t\targs.%[1]s = pulumi.ToSecret(args.%[1]s).(%[2]s)\n", pkg.fieldName(r, p), pkg.outputType(p.Type))
+
+		fmt.Fprintf(w, "\t\targs.%[1]s = pulumi.ToSecret(args.%[1]s).(%[2]s)\n", pkg.fieldName(r, p), pkg.typeString(p.Type))
 		fmt.Fprintf(w, "\t}\n")
 	}
 	if len(secretProps) > 0 {