cty: UnknownAsNull accepts marked values and preserves marks

This change was sponsored by Spacelift on behalf of the OpenTofu project.

Author: apparentlymart

CHANGELOG.md

@@ -1,5 +1,6 @@
 # 1.16.4 (Unreleased)
 
+* `cty.UnknownAsNull` now accepts marked values and preserves the given marks in its result. Previously it had no direct support for marks and so would either panic or return incorrect results when given marked values.
 
 # 1.16.3 (May 16, 2025)
 

cty/unknown_as_null.go

@@ -8,6 +8,11 @@ package cty
 // represent unknowns, such as JSON, as long as the caller does not need to
 // retain the unknown value information.
 func UnknownAsNull(val Value) Value {
+	if val.IsMarked() {
+		val, valMarks := val.Unmark()
+		return UnknownAsNull(val).WithMarks(valMarks)
+	}
+
 	ty := val.Type()
 	switch {
 	case val.IsNull():

cty/unknown_as_null_test.go

@@ -179,6 +179,100 @@ func TestUnknownAsNull(t *testing.T) {
 				"greeting": NullVal(String),
 			}),
 		},
+
+		// Marks should be accepted and preserved verbatim
+		{
+			StringVal("hello").Mark("..."),
+			StringVal("hello").Mark("..."),
+		},
+		{
+			UnknownVal(String).Mark("..."),
+			NullVal(String).Mark("..."),
+		},
+		{
+			DynamicVal.Mark("..."),
+			NullVal(DynamicPseudoType).Mark("..."),
+		},
+		{
+			ListVal([]Value{
+				UnknownVal(String),
+			}).Mark("..."),
+			ListVal([]Value{
+				NullVal(String),
+			}).Mark("..."),
+		},
+		{
+			ListVal([]Value{
+				UnknownVal(String).Mark("..."),
+			}),
+			ListVal([]Value{
+				NullVal(String).Mark("..."),
+			}),
+		},
+		{
+			SetVal([]Value{
+				UnknownVal(String),
+			}).Mark("..."),
+			SetVal([]Value{
+				NullVal(String),
+			}).Mark("..."),
+		},
+		{
+			SetVal([]Value{
+				UnknownVal(String).Mark("..."),
+			}),
+			SetVal([]Value{
+				NullVal(String).Mark("..."),
+			}),
+		},
+		{
+			TupleVal([]Value{
+				UnknownVal(String),
+			}).Mark("..."),
+			TupleVal([]Value{
+				NullVal(String),
+			}).Mark("..."),
+		},
+		{
+			TupleVal([]Value{
+				UnknownVal(String).Mark("..."),
+			}),
+			TupleVal([]Value{
+				NullVal(String).Mark("..."),
+			}),
+		},
+		{
+			MapVal(map[string]Value{
+				"greeting": UnknownVal(String),
+			}).Mark("..."),
+			MapVal(map[string]Value{
+				"greeting": NullVal(String),
+			}).Mark("..."),
+		},
+		{
+			MapVal(map[string]Value{
+				"greeting": UnknownVal(String).Mark("..."),
+			}),
+			MapVal(map[string]Value{
+				"greeting": NullVal(String).Mark("..."),
+			}),
+		},
+		{
+			ObjectVal(map[string]Value{
+				"greeting": UnknownVal(String),
+			}).Mark("..."),
+			ObjectVal(map[string]Value{
+				"greeting": NullVal(String),
+			}).Mark("..."),
+		},
+		{
+			ObjectVal(map[string]Value{
+				"greeting": UnknownVal(String).Mark("..."),
+			}),
+			ObjectVal(map[string]Value{
+				"greeting": NullVal(String).Mark("..."),
+			}),
+		},
 	}
 
 	for _, test := range tests {