Re: [PATCHv2] gdb/python: add facility to add values into the history

[Andrew Burgess <andrew.burgess@embecosm.com>]

* Eli Zaretskii <eliz@gnu.org> [2021-08-26 12:40:18 +0300]:

> > Date: Thu, 26 Aug 2021 10:20:02 +0100
> > From: Andrew Burgess <andrew.burgess@embecosm.com>
> > Cc: gdb-patches@sourceware.org
> > 
> > * Eli Zaretskii <eliz@gnu.org> [2021-08-25 21:01:50 +0300]:
> > 
> > > > From: Andrew Burgess <andrew.burgess@embecosm.com>
> > > > Date: Wed, 25 Aug 2021 18:27:19 +0100
> > > > 
> > > > +* Python API
> > > > +
> > > > +  ** New function gdb.add_history(), which takes a gdb.Value object
> > > > +     and adds the value to GDB's history list.  An integer, the index
> > >                  ^^^^^^^^^
> > > "its value", right?
> > 
> > I don't know, that doesn't sound right to me.  'its value' seems to
> > imply a value that belongs to someone/something, but I don't think
> > that's the case here.
> > 
> > Maybe, '...takes a gdb.Value object and adds it to GDB's history list.' ?
> 
> No, that's worse, because you don't add the Python object to the
> history.
> 
> How about if you use the same wording you suggested for the manual:
> "the value it represents"?

Excellent, I'll do that.  The final version of the patch I pushed is
below.

Thanks for the review.

Andrew

---

commit 10effdd0d48947b41eb89426d0a408b2421c3d27
Author: Andrew Burgess <andrew.burgess@embecosm.com>
Date:   Fri Jul 30 12:56:34 2021 +0100

    gdb/python: new function to add values into GDB's history
    
    The guile API has (history-append! <value>) to add values into GDB's
    history list.  There is currently no equivalent in the Python API.
    
    This commit adds gdb.add_history(<value>) to the Python API, this
    function takes <value> a gdb.Value (or anything that can be passed to
    the constructor of gdb.Value), and adds the value it represents to
    GDB's history list.  The index of the newly added value is returned.

diff --git a/gdb/NEWS b/gdb/NEWS
index ec3058ea118..f9485520438 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -10,6 +10,13 @@ maint show backtrace-on-fatal-signal
   fatal signal.  This only supported on some platforms where the
   backtrace and backtrace_symbols_fd functions are available.
 
+* Python API
+
+  ** New function gdb.add_history(), which takes a gdb.Value object
+     and adds the value it represents to GDB's history list.  An
+     integer, the index of the new item in the history list, is
+     returned.
+
 *** Changes in GDB 11
 
 * The 'set disassembler-options' command now supports specifying options
diff --git a/gdb/doc/python.texi b/gdb/doc/python.texi
index f4865b3d6a6..d8f682a091c 100644
--- a/gdb/doc/python.texi
+++ b/gdb/doc/python.texi
@@ -346,6 +346,20 @@
 @code{gdb.Value} (@pxref{Values From Inferior}).
 @end defun
 
+@defun gdb.add_history (value)
+Takes @var{value}, an instance of @code{gdb.Value} (@pxref{Values From
+Inferior}), and appends the value this object represents to
+@value{GDBN}'s value history (@pxref{Value History}), and return an
+integer, its history number.  If @var{value} is not a
+@code{gdb.Value}, it is is converted using the @code{gdb.Value}
+constructor.  If @var{value} can't be converted to a @code{gdb.Value}
+then a @code{TypeError} is raised.
+
+When a command implemented in Python prints a single @code{gdb.Value}
+as its result, then placing the value into the history will allow the
+user convenient access to those values via CLI history facilities.
+@end defun
+
 @findex gdb.convenience_variable
 @defun gdb.convenience_variable (name)
 Return the value of the convenience variable (@pxref{Convenience
diff --git a/gdb/python/py-value.c b/gdb/python/py-value.c
index 8df8a15f8d6..26d5940f842 100644
--- a/gdb/python/py-value.c
+++ b/gdb/python/py-value.c
@@ -1960,6 +1960,33 @@ gdbpy_history (PyObject *self, PyObject *args)
   return value_to_value_object (res_val);
 }
 
+/* Add a gdb.Value into GDB's history, and return (as an integer) the
+   position of the newly added value.  */
+PyObject *
+gdbpy_add_history (PyObject *self, PyObject *args)
+{
+  PyObject *value_obj;
+
+  if (!PyArg_ParseTuple (args, "O", &value_obj))
+    return nullptr;
+
+  struct value *value = convert_value_from_python (value_obj);
+  if (value == nullptr)
+    return nullptr;
+
+  try
+    {
+      int idx = record_latest_value (value);
+      return gdb_py_object_from_longest (idx).release ();
+    }
+  catch (const gdb_exception &except)
+    {
+      GDB_PY_HANDLE_EXCEPTION (except);
+    }
+
+  return nullptr;
+}
+
 /* Return the value of a convenience variable.  */
 PyObject *
 gdbpy_convenience_variable (PyObject *self, PyObject *args)
diff --git a/gdb/python/python-internal.h b/gdb/python/python-internal.h
index 690d2fb43c0..0e140f1af61 100644
--- a/gdb/python/python-internal.h
+++ b/gdb/python/python-internal.h
@@ -412,6 +412,7 @@ extern enum ext_lang_rc gdbpy_get_matching_xmethod_workers
 
 \f
 PyObject *gdbpy_history (PyObject *self, PyObject *args);
+PyObject *gdbpy_add_history (PyObject *self, PyObject *args);
 PyObject *gdbpy_convenience_variable (PyObject *self, PyObject *args);
 PyObject *gdbpy_set_convenience_variable (PyObject *self, PyObject *args);
 PyObject *gdbpy_breakpoints (PyObject *, PyObject *);
diff --git a/gdb/python/python.c b/gdb/python/python.c
index e42cbc4fd5e..6af9c722e7b 100644
--- a/gdb/python/python.c
+++ b/gdb/python/python.c
@@ -2076,6 +2076,8 @@ PyMethodDef python_GdbMethods[] =
 {
   { "history", gdbpy_history, METH_VARARGS,
     "Get a value from history" },
+  { "add_history", gdbpy_add_history, METH_VARARGS,
+    "Add a value to the value history list" },
   { "execute", (PyCFunction) execute_gdb_command, METH_VARARGS | METH_KEYWORDS,
     "execute (command [, from_tty] [, to_string]) -> [String]\n\
 Evaluate command, a string, as a gdb CLI command.  Optionally returns\n\
diff --git a/gdb/testsuite/gdb.python/py-value.exp b/gdb/testsuite/gdb.python/py-value.exp
index eca4a474727..d9f1a76a388 100644
--- a/gdb/testsuite/gdb.python/py-value.exp
+++ b/gdb/testsuite/gdb.python/py-value.exp
@@ -575,6 +575,31 @@ proc test_value_from_buffer {} {
 	   "attempt to construct value with string as type"
 }
 
+# Test the gdb.add_history API.
+proc test_add_to_history {} {
+    # Add a gdb.Value to the value history list.
+    gdb_test_no_output "python idx = gdb.add_history(gdb.Value(42))" \
+	"add value 42 to the history list"
+    gdb_test "python print (\"$%d = %s\" % (idx, gdb.history (idx)))" \
+	" = 42" "print value 42 from the history list"
+    set idx [get_python_valueof "idx" "**DEFAULT**" "get idx for value 42"]
+    gdb_test "print \$${idx}" " = 42"
+
+    # Add something to the history list that can be converted into a
+    # gdb.Value.
+    gdb_test_no_output "python idx = gdb.add_history(84)" \
+	"add value to 84 to the history list"
+    gdb_test "python print (\"$%d = %s\" % (idx, gdb.history (idx)))" \
+	" = 84" "print value 84 from the history list"
+    set idx [get_python_valueof "idx" "**DEFAULT**" "get idx for value 84"]
+    gdb_test "print \$${idx}" " = 84"
+
+    # Try adding something that can't be converted to a gdb.Value,
+    # this should give an error.
+    gdb_test "python idx = gdb.add_history(gdb.GdbError(\"an error\"))" \
+	"TypeError: Could not convert Python object: .*"
+}
+
 # Build C version of executable.  C++ is built later.
 if { [build_inferior "${binfile}" "c"] < 0 } {
     return -1
@@ -594,6 +619,7 @@ test_objfiles
 test_parse_and_eval
 test_value_hash
 test_float_conversion
+test_add_to_history
 
 # The following tests require execution.