nonsensitive: no longer produces error when applied to nonsensitive values (#33856)

* Proposing fix to #31693 (not always possible to apply nonsensitive)

https://github.com/hashicorp/terraform/issues/31693

* hashicorp#31693 not always possible to apply nonsensitive

updated documentation

* Update sensitive_test.go

Fixing tests

* Corrections as per https://github.com/hashicorp/terraform/pull/33856#discussion_r1330042125

internal/lang/funcs/sensitive.go

@@ -52,9 +52,6 @@ var NonsensitiveFunc = function.New(&function.Spec{
 		return args[0].Type(), nil
 	},
 	Impl: func(args []cty.Value, retType cty.Type) (ret cty.Value, err error) {
-		if args[0].IsKnown() && !args[0].HasMark(marks.Sensitive) {
-			return cty.DynamicVal, function.NewArgErrorf(0, "the given value is not sensitive, so this call is redundant")
-		}
 		v, m := args[0].Unmark()
 		delete(m, marks.Sensitive) // remove the sensitive marking
 		return v.WithMarks(m), nil

internal/lang/funcs/sensitive_test.go

@@ -130,16 +130,16 @@ func TestNonsensitive(t *testing.T) {
 			``,
 		},
 
-		// Passing a value that is already non-sensitive is an error,
-		// because this function should always be used with specific
-		// intention, not just as a "make everything visible" hammer.
+		// Passing a value that is already non-sensitive is not an error,
+		// as this function may be used with specific to ensure that all
+		// values are indeed non-sensitive
 		{
 			cty.NumberIntVal(1),
-			`the given value is not sensitive, so this call is redundant`,
+			``,
 		},
 		{
 			cty.NullVal(cty.String),
-			`the given value is not sensitive, so this call is redundant`,
+			``,
 		},
 
 		// Unknown values may become sensitive once they are known, so we

website/docs/language/functions/nonsensitive.mdx

@@ -73,10 +73,8 @@ due to an inappropriate call to `nonsensitive` in your module, that's a bug in
 your module and not a bug in Terraform itself.
 **Use this function sparingly and only with due care.**
 
-`nonsensitive` will return an error if you pass a value that isn't marked
-as sensitive, because such a call would be redundant and potentially confusing
-or misleading to a future maintainer of your module. Use `nonsensitive` only
-after careful consideration and with definite intent.
+`nonsensitive` will make no changes to values that aren't marked as sensitive, even though such a call may be redundant and potentially confusing.
+Use `nonsensitive` only after careful consideration and with definite intent.
 
 Consider including a comment adjacent to your call to explain to future
 maintainers what makes the usage safe and thus what invariants they must take