Gate complex default warning on class check

`new_property()` warned for any non-scalar `default` before checking whether the
value matched the declared property class.

With an invalid non-scalar default such as
`new_property(class_integer, default = c("x", "y"))`, this warning was emitted
before the class check, so callers saw both the new deprecation warning and the
existing type error. Under `options(warn = 2)`, they only saw the
warning-as-error and lost the real validation message.

Move this warning after confirming `class_inherits(default, class)` so invalid
defaults keep the existing clear error path.

Add regression coverage for the invalid complex default path with warnings
converted to errors.

Author: t-kalinowski

DESCRIPTION

@@ -37,7 +37,8 @@ Suggests:
     methods,
     rmarkdown,
     testthat (>= 3.2.0),
-    tibble
+    tibble,
+    withr
 VignetteBuilder:
     knitr
 Config/build/compilation-database: true

R/property.R

@@ -168,10 +168,10 @@ check_prop_default <- function(
     return()
   }
 
-  if (!is_scalar(default)) {
-    warn_prop_default_complex(default, default_expr, call)
-  }
   if (class_inherits(default, class)) {
+    if (!is_scalar(default)) {
+      warn_prop_default_complex(default, default_expr, call)
+    }
     return()
   }
 

tests/testthat/test-property.R

@@ -434,6 +434,15 @@ describe("new_property()", {
     })
   })
 
+  it("rejects invalid complex defaults without warning first", {
+    withr::local_options(list(warn = 2))
+
+    expect_error(
+      new_property(class_integer, default = c("x", "y")),
+      "`default` must be an instance of <integer>"
+    )
+  })
+
   it("warns if default is not a scalar or quoted call", {
     expect_snapshot({
       . <- new_property(class_integer, default = c(any = 1L))