Commenting out const in def_buffer(... const). With this, test_buffers builds and runs with PYBIND11_USE_SMART_HOLDER_AS_DEFAULT. Explanation why the const needs to be removed, or fix elsewhere, is still needed, but left for later.

rwgk · rwgk · commit 634953130661 · 2021-02-09T06:47:45.000-08:00
diff --git a/include/pybind11/pybind11.h b/include/pybind11/pybind11.h
@@ -1409,7 +1409,8 @@ class class_ : public detail::generic_type {
 
     template <typename Return, typename Class, typename... Args>
     class_ &def_buffer(Return (Class::*func)(Args...) const) {
-        return def_buffer([func] (const type &obj) { return (obj.*func)(); });
+        // NEEDED: Explanation why the const needs to be removed, or fix elsewhere.
+        return def_buffer([func] (/*const*/ type &obj) { return (obj.*func)(); });
     }
 
     template <typename C, typename D, typename... Extra>

Original file line number	Diff line number	Diff line change
`@@ -1409,7 +1409,8 @@ class class_ : public detail::generic_type {`
`1409`	`1409`
`1410`	`1410`	`template <typename Return, typename Class, typename... Args>`
`1411`	`1411`	`class_ &def_buffer(Return (Class::*func)(Args...) const) {`
`1412`		`- return def_buffer([func] (const type &obj) { return (obj.*func)(); });`
	`1412`	`+ // NEEDED: Explanation why the const needs to be removed, or fix elsewhere.`
	`1413`	`+ return def_buffer([func] (/const/ type &obj) { return (obj.*func)(); });`
`1413`	`1414`	`}`
`1414`	`1415`
`1415`	`1416`	`template <typename C, typename D, typename... Extra>`