template variables may be entirely unknown

While the evaluator can deal with unknown template variables, if the
entire map of variables is unknown, we can't create the map and need to
short-circuit the call.

Author: jbardin

internal/lang/funcs/filesystem.go

@@ -137,7 +137,7 @@ func MakeTemplateFileFunc(baseDir string, funcsCb func() (funcs map[string]funct
 
 			vars, varsMarks := args[1].UnmarkDeep()
 
-			if !pathArg.IsKnown() {
+			if !pathArg.IsKnown() || !vars.IsKnown() {
 				return cty.UnknownVal(retType).WithMarks(pathMarks, varsMarks), nil
 			}
 

internal/lang/funcs/filesystem_test.go

@@ -216,6 +216,12 @@ func TestTemplateFile(t *testing.T) {
 			cty.StringVal("- a\n- b\n- c\n").Mark("path").Mark("var"),
 			``,
 		},
+		{
+			cty.StringVal("testdata/list.tmpl").Mark("path"),
+			cty.UnknownVal(cty.Map(cty.String)),
+			cty.DynamicVal.Mark("path"),
+			``,
+		},
 		{
 			cty.StringVal("testdata/list.tmpl").Mark("path"),
 			cty.ObjectVal(map[string]cty.Value{