Change extension language pretty-printers to use value API

This changes the extension language pretty-printers to use the value
API.

Note that new functions were needed, for both Guile and Python.
Currently both languages always wrap values by removing the values
from the value chain.  This makes sense to avoid strange behavior with
watchpoints, and to avoid excessive memory use.  However, when
printing, it's important to leave the passed-in value untouched, in
case pretty-printing does nothing -- that way the caller can still
access it.

gdb/ChangeLog
2020-03-13  Tom Tromey  <tom@tromey.com>

	* valprint.c (do_val_print): Update.
	* python/python-internal.h (gdbpy_apply_val_pretty_printer): Take
	a struct value.
	(value_to_value_object_no_release): Declare.
	* python/py-value.c (value_to_value_object_no_release): New
	function.
	* python/py-prettyprint.c (gdbpy_apply_val_pretty_printer): Take a
	struct value.
	* guile/scm-value.c (vlscm_scm_from_value_no_release): New
	function.
	* guile/scm-pretty-print.c (gdbscm_apply_val_pretty_printer): Take
	a struct value.
	* guile/guile-internal.h (vlscm_scm_from_value_no_release):
	Declare.
	(gdbscm_apply_val_pretty_printer): Take a struct value.
	* extension.h (apply_ext_lang_val_pretty_printer): Take a struct
	value.
	* extension.c (apply_ext_lang_val_pretty_printer): Take a struct
	value.
	* extension-priv.h (struct extension_language_ops)
	<apply_val_pretty_printer>: Take a struct value.
	* cp-valprint.c (cp_print_value): Create a struct value.
	(cp_print_value): Update.

1 files changed, 18 insertions, 0 deletions

diff --git a/gdb/guile/scm-value.c b/gdb/guile/scm-value.c
index 020b5e1..53b373e 100644
--- a/gdb/guile/scm-value.c
+++ b/gdb/guile/scm-value.c
@@ -261,6 +261,24 @@ vlscm_scm_from_value (struct value *value)
   return v_scm;
 }
 
+/* Create a new <gdb:value> object that encapsulates VALUE.
+   The value is not released from the all_values chain.  */
+
+SCM
+vlscm_scm_from_value_no_release (struct value *value)
+{
+  /* N.B. It's important to not cause any side-effects until we know the
+     conversion worked.  */
+  SCM v_scm = vlscm_make_value_smob ();
+  value_smob *v_smob = (value_smob *) SCM_SMOB_DATA (v_scm);
+
+  value_incref (value);
+  v_smob->value = value;
+  vlscm_remember_scheme_value (v_smob);
+
+  return v_scm;
+}
+
 /* Returns the <gdb:value> object in SELF.
    Throws an exception if SELF is not a <gdb:value> object.  */