[PATCH] python: Provide textual representation for Inferior and Objfile

[Simon Marchi <simon dot marchi at ericsson dot com>]

Printing a GDB Python object is notoriously not helpful:

>>> print(gdb.selected_inferior())
<gdb.Inferior object at 0x7fea59aed198>
>>> print(gdb.objfiles())
[<gdb.Objfile object at 0x7fea59b57c90>]

This makes printing debug traces more difficult than it should be.  This
patch provides some repr() implementation for these two types (more to
come if people agree with the idea, but I want to test the water first).
Here's the same example as above, but with this patch:

>>> print(gdb.selected_inferior())
<gdb.Inferior num=1>
>>> print(gdb.objfiles())
[<gdb.Objfile filename=/home/emaisin/build/binutils-gdb-gcc-git/gdb/test>]

I implemented repr rather than str, because when printing a list (or
another container I suppose), Python calls the repr method of the
elements.  This is useful when printing a list of inferiors or objfiles.
The print(gdb.objfiles()) above would not have worked if I had
implemented str.

I found this post useful to understand the difference between repr and
str:

  https://stackoverflow.com/questions/1436703/difference-between-str-and-repr

In your opinion, does this require an announcement in NEWS and an entry
in the manual?  I don't think the output of repr() should be considered
stable, as we could change it over time to make it more useful.  Maybe
that should be documented?

gdb/ChangeLog:

	* python/py-inferior.c (infpy_repr): New.
	(inferior_object_type): Register infpy_repr.
	* python/py-objfile.c (objfpy_repr): New.
	(objfile_object_type): Register objfpy_repr.

gdb/testsuite/ChangeLog:

	* gdb.python/py-inferior.exp: Test repr() of gdb.Inferior.
	* gdb.python/py-objfile.exp: Test repr() of gdb.Objfile.
	* gdb.python/py-symtab.exp: Update test printing an objfile.
---
 gdb/python/py-inferior.c                 | 17 ++++++++++++++++-
 gdb/python/py-objfile.c                  | 17 ++++++++++++++++-
 gdb/testsuite/gdb.python/py-inferior.exp | 14 +++++++++++++-
 gdb/testsuite/gdb.python/py-objfile.exp  |  7 +++++++
 gdb/testsuite/gdb.python/py-symtab.exp   |  2 +-
 5 files changed, 53 insertions(+), 4 deletions(-)

diff --git a/gdb/python/py-inferior.c b/gdb/python/py-inferior.c
index 1cf37296973..56019bf9e05 100644
--- a/gdb/python/py-inferior.c
+++ b/gdb/python/py-inferior.c
@@ -860,6 +860,21 @@ infpy_thread_from_thread_handle (PyObject *self, PyObject *args, PyObject *kw)
   return result;
 }
 
+/* Implement repr() for gdb.Inferior.  */
+
+static PyObject *
+infpy_repr (PyObject *obj)
+{
+  inferior_object *self = (inferior_object *) obj;
+  inferior *inf = self->inferior;
+
+  if (inf == nullptr)
+    return PyString_FromString ("<gdb.Inferior (invalid)>");
+
+  return PyString_FromFormat ("<gdb.Inferior num=%d, pid=%d>",
+			      inf->num, inf->pid);
+}
+
 
 static void
 infpy_dealloc (PyObject *obj)
@@ -991,7 +1006,7 @@ PyTypeObject inferior_object_type =
   0,				  /* tp_getattr */
   0,				  /* tp_setattr */
   0,				  /* tp_compare */
-  0,				  /* tp_repr */
+  infpy_repr,			  /* tp_repr */
   0,				  /* tp_as_number */
   0,				  /* tp_as_sequence */
   0,				  /* tp_as_mapping */
diff --git a/gdb/python/py-objfile.c b/gdb/python/py-objfile.c
index c2b40ff5352..61d3a158198 100644
--- a/gdb/python/py-objfile.c
+++ b/gdb/python/py-objfile.c
@@ -456,6 +456,21 @@ objfpy_add_separate_debug_file (PyObject *self, PyObject *args, PyObject *kw)
   Py_RETURN_NONE;
 }
 
+/* Implement repr() for gdb.Objfile.  */
+
+static PyObject *
+objfpy_repr (PyObject *self_)
+{
+  objfile_object *self = (objfile_object *) self_;
+  objfile *obj = self->objfile;
+
+  if (obj == nullptr)
+    return PyString_FromString ("<gdb.Objfile (invalid)>");
+
+  return PyString_FromFormat ("<gdb.Objfile filename=%s>",
+			      objfile_filename (obj));
+}
+
 /* Subroutine of gdbpy_lookup_objfile_by_build_id to simplify it.
    Return non-zero if STRING is a potentially valid build id.  */
 
@@ -709,7 +724,7 @@ PyTypeObject objfile_object_type =
   0,				  /*tp_getattr*/
   0,				  /*tp_setattr*/
   0,				  /*tp_compare*/
-  0,				  /*tp_repr*/
+  objfpy_repr,			  /*tp_repr*/
   0,				  /*tp_as_number*/
   0,				  /*tp_as_sequence*/
   0,				  /*tp_as_mapping*/
diff --git a/gdb/testsuite/gdb.python/py-inferior.exp b/gdb/testsuite/gdb.python/py-inferior.exp
index a943d5f214e..ce3d7d63010 100644
--- a/gdb/testsuite/gdb.python/py-inferior.exp
+++ b/gdb/testsuite/gdb.python/py-inferior.exp
@@ -45,7 +45,7 @@ if ![runto_main] then {
 # Test basic gdb.Inferior attributes and methods.
 
 gdb_py_test_silent_cmd "python inferiors = gdb.inferiors ()" "get inferiors list" 1
-gdb_test "python print (inferiors)" "\\(<gdb.Inferior object at 0x\[\[:xdigit:\]\]+>,\\)" "verify inferiors list"
+gdb_test "python print (inferiors)" "\\(<gdb.Inferior num=1, pid=$decimal>,\\)" "verify inferiors list"
 gdb_py_test_silent_cmd "python i0 = inferiors\[0\]" "get first inferior" 0
 
 gdb_test "python print ('result = %s' % (i0 == inferiors\[0\]))" " = True" "test equality comparison (true)"
@@ -266,3 +266,15 @@ with_test_prefix "selected_inferior" {
     gdb_test "inferior 1" ".*" "switch back to first inferior"
     gdb_test_no_output "remove-inferiors 3" "remove second inferior"
 }
+
+# Test repr()/str()
+with_test_prefix "__repr__" {
+    gdb_test "add-inferior" "Added inferior 4" "add inferior 4"
+    gdb_py_test_silent_cmd "python infs = gdb.inferiors()" "get inferior list" 1
+    gdb_test "python print (infs\[0\])" "<gdb.Inferior num=1, pid=$decimal>"
+    gdb_test "python print (infs)" "\\\(<gdb.Inferior num=1, pid=$decimal>, <gdb.Inferior num=4, pid=$decimal>\\\)" \
+	"print all inferiors 1"
+    gdb_test_no_output "remove-inferiors 4"
+    gdb_test "python print (infs)" "\\\(<gdb.Inferior num=1, pid=$decimal>, <gdb.Inferior \\\(invalid\\\)>\\\)" \
+	"print all inferiors 2"
+}
diff --git a/gdb/testsuite/gdb.python/py-objfile.exp b/gdb/testsuite/gdb.python/py-objfile.exp
index 6e81750cfe9..240de29efd1 100644
--- a/gdb/testsuite/gdb.python/py-objfile.exp
+++ b/gdb/testsuite/gdb.python/py-objfile.exp
@@ -45,6 +45,8 @@ gdb_test "python print (objfile.filename)" "${testfile}" \
 gdb_test "python print (objfile.username)" "${testfile}" \
   "Get objfile user name"
 
+gdb_test "python print (objfile)" "<gdb.Objfile filename=[string_to_regexp ${binfile}]>"
+
 gdb_test_no_output "python dir(objfile)"
 
 gdb_test "python print (gdb.lookup_objfile (\"${testfile}\").filename)" \
@@ -149,3 +151,8 @@ if [remote_file host exists "${symlink_binary}"] {
     gdb_test "python print (gdb.lookup_objfile (\"${symlink_binary}\").filename)" \
 	"${testfile}" "gdb.lookup_objfile of symlinked binary"
 }
+
+# Test printing an Objfile object that is no longer valid.
+gdb_py_test_silent_cmd "python objfile = gdb.objfiles()\[0\]" "get first objfile" 1
+gdb_file_cmd ${binfile}
+gdb_test "python print(objfile)" "<gdb.Objfile \\\(invalid\\\)>"
\ No newline at end of file
diff --git a/gdb/testsuite/gdb.python/py-symtab.exp b/gdb/testsuite/gdb.python/py-symtab.exp
index f504362526f..4083b3b4475 100644
--- a/gdb/testsuite/gdb.python/py-symtab.exp
+++ b/gdb/testsuite/gdb.python/py-symtab.exp
@@ -66,7 +66,7 @@ gdb_test "python print (sal.is_valid())" "True" "test sal.is_valid"
 
 # Test symbol table.
 gdb_test "python print (symtab.filename)" ".*${py_symbol_c}" "test symtab.filename"
-gdb_test "python print (symtab.objfile)" "<gdb.Objfile object at ${hex}>" "test symtab.objfile"
+gdb_test "python print (symtab.objfile)" "<gdb.Objfile filename=${binfile}>" "test symtab.objfile"
 gdb_test "python print (symtab.fullname())" ".*${full_py_symbol_c}" "test symtab.fullname"
 gdb_test "python print (symtab.is_valid())" "True" "test symtab.is_valid()"
 gdb_test "python print (\"qq\" in global_symbols)" "True" "test qq in global symbols"
-- 
2.19.0