Patchwork Fix Python completion when using the "complete" command

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Submitter Sergio Durigan Junior
Date April 8, 2015, 7:58 p.m.
Message ID <87384a1jeo.fsf@redhat.com>
Download mbox | patch
Permalink /patch/6104/
State New
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Comments

Sergio Durigan Junior - April 8, 2015, 7:58 p.m.
On Wednesday, April 08 2015, Keith Seitz wrote:

>>> >+   This function is usually called twice: one when we are figuring out
>
> nitpick (sorry): "once" instead of "one"

Thanks, fixed.

> This looks good to me.
>
> I have applied this patch to my completer branch, and I can verify
> that it fixes the (other) completion problems I've seen. I recommend
> that a maintainer approve this.

Thanks for the review, Keith!

Here is the updated patch + ChangeLog entry.
Doug Evans - April 8, 2015, 8:39 p.m.
Sergio Durigan Junior writes:
 > On Wednesday, April 08 2015, Keith Seitz wrote:
 > 
 > >>> >+   This function is usually called twice: one when we are figuring out
 > >
 > > nitpick (sorry): "once" instead of "one"
 > 
 > Thanks, fixed.
 > 
 > > This looks good to me.
 > >
 > > I have applied this patch to my completer branch, and I can verify
 > > that it fixes the (other) completion problems I've seen. I recommend
 > > that a maintainer approve this.
 > 
 > Thanks for the review, Keith!
 > 
 > Here is the updated patch + ChangeLog entry.
 > 
 > -- 
 > Sergio
 > GPG key ID: 237A 54B1 0287 28BF 00EF  31F4 D0EB 7628 65FC 5E36
 > Please send encrypted e-mail if possible
 > http://sergiodj.net/
 > 
 > gdb/ChangeLog:
 > 2015-04-08  Sergio Durigan Junior  <sergiodj@redhat.com>
 > 
 > 	PR python/16699
 > 	* python/py-cmd.c (cmdpy_completer_helper): Adjust function to not
 > 	use a caching mechanism.  Adjust comments and code to reflect
 > 	that.  Replace 'sizeof' by 'strlen' when fetching 'wordobj'.
 > 	(cmdpy_completer_handle_brkchars): Adjust call to
 > 	cmdpy_completer_helper.  Call Py_XDECREF for 'resultobj'.
 > 	(cmdpy_completer): Likewise.
 > 
 > gdb/testsuite/ChangeLog:
 > 2015-04-08  Keith Seitz  <keiths@redhat.com>
 > 
 > 	PR python/16699
 > 	* gdb.python/py-completion.exp: New tests for completion.
 > 	* gdb.python/py-completion.py (CompleteLimit1): New class.
 > 	(CompleteLimit2): Likewise.
 > 	(CompleteLimit3): Likewise.
 > 	(CompleteLimit4): Likewise.
 > 	(CompleteLimit5): Likewise.
 > 	(CompleteLimit6): Likewise.
 > 	(CompleteLimit7): Likewise.

LGTM.

One comment below.

 > +  resultobj = PyObject_CallMethodObjArgs ((PyObject *) obj, complete_cst,
 > +					  textobj, wordobj, NULL);
 > +  Py_DECREF (textobj);
 > +  Py_DECREF (wordobj);
 > +  if (!resultobj)
 > +    {
 > +      /* Just swallow errors here.  */
 > +      PyErr_Clear ();
 >      }

I realize this is just copying the previous code,
but does swallowing errors here make it hard to debug problems
in the completer function?
Is this something we want to address in a future patch?
Sergio Durigan Junior - April 8, 2015, 10:29 p.m.
On Wednesday, April 08 2015, Doug Evans wrote:

>  > +  resultobj = PyObject_CallMethodObjArgs ((PyObject *) obj, complete_cst,
>  > +					  textobj, wordobj, NULL);
>  > +  Py_DECREF (textobj);
>  > +  Py_DECREF (wordobj);
>  > +  if (!resultobj)
>  > +    {
>  > +      /* Just swallow errors here.  */
>  > +      PyErr_Clear ();
>  >      }
>
> I realize this is just copying the previous code,
> but does swallowing errors here make it hard to debug problems
> in the completer function?
> Is this something we want to address in a future patch?

Thanks for the review, Doug.

You have a valid point: swallowing errors in this part of the code does
make it hard to debug problems in the user-provided completer
functions.  And a small hack in the code proved me that it should be
fairly easy to print the error instead, just like cmdpy_function already
does.  I will see if I can prepare a patch to do that.

Meanwhile, I pushed the current patch upstream.

  <https://sourceware.org/ml/gdb-cvs/2015-04/msg00062.html>
  6d62641c832525382336c1b04731d85cb6c398e7

Thanks,

Patch

diff --git a/gdb/python/py-cmd.c b/gdb/python/py-cmd.c
index 1d89912..017d0b6 100644
--- a/gdb/python/py-cmd.c
+++ b/gdb/python/py-cmd.c
@@ -210,85 +210,70 @@  cmdpy_function (struct cmd_list_element *command, char *args, int from_tty)
 /* Helper function for the Python command completers (both "pure"
    completer and brkchar handler).  This function takes COMMAND, TEXT
    and WORD and tries to call the Python method for completion with
-   these arguments.  It also takes HANDLE_BRKCHARS_P, an argument to
-   identify whether it is being called from the brkchar handler or
-   from the "pure" completer.  In the first case, it effectively calls
-   the Python method for completion, and records the PyObject in a
-   static variable (used as a "cache").  In the second case, it just
-   returns that variable, without actually calling the Python method
-   again.  This saves us one Python method call.
-
-   The reason for this two step dance is that we need to know the set
-   of "brkchars" to use early on, before we actually try to perform
-   the completion.  But if a Python command supplies a "complete"
-   method then we have to call that method first: it may return as its
-   result the kind of completion to perform and that will in turn
-   specify which brkchars to use.  IOW, we need the result of the
-   "complete" method before we actually perform the completion.
-
-   It is important to mention that this function is built on the
-   assumption that the calls to cmdpy_completer_handle_brkchars and
-   cmdpy_completer will be subsequent with nothing intervening.  This
-   is true for our completer mechanism.
+   these arguments.
+
+   This function is usually called twice: once when we are figuring out
+   the break characters to be used, and another to perform the real
+   completion itself.  The reason for this two step dance is that we
+   need to know the set of "brkchars" to use early on, before we
+   actually try to perform the completion.  But if a Python command
+   supplies a "complete" method then we have to call that method
+   first: it may return as its result the kind of completion to
+   perform and that will in turn specify which brkchars to use.  IOW,
+   we need the result of the "complete" method before we actually
+   perform the completion.  The only situation when this function is
+   not called twice is when the user uses the "complete" command: in
+   this scenario, there is no call to determine the "brkchars".
+
+   Ideally, it would be nice to cache the result of the first call (to
+   determine the "brkchars") and return this value directly in the
+   second call (to perform the actual completion).  However, due to
+   the peculiarity of the "complete" command mentioned above, it is
+   possible to put GDB in a bad state if you perform a TAB-completion
+   and then a "complete"-completion sequentially.  Therefore, we just
+   recalculate everything twice for TAB-completions.
 
    This function returns the PyObject representing the Python method
    call.  */
 
 static PyObject *
 cmdpy_completer_helper (struct cmd_list_element *command,
-			const char *text, const char *word,
-			int handle_brkchars_p)
+			const char *text, const char *word)
 {
   cmdpy_object *obj = (cmdpy_object *) get_cmd_context (command);
   PyObject *textobj, *wordobj;
-  /* This static variable will server as a "cache" for us, in order to
-     store the PyObject that results from calling the Python
-     function.  */
-  static PyObject *resultobj = NULL;
+  PyObject *resultobj;
 
-  if (handle_brkchars_p)
+  if (obj == NULL)
+    error (_("Invalid invocation of Python command object."));
+  if (!PyObject_HasAttr ((PyObject *) obj, complete_cst))
     {
-      /* If we were called to handle brkchars, it means this is the
-	 first function call of two that will happen in a row.
-	 Therefore, we need to call the completer ourselves, and cache
-	 the return value in the static variable RESULTOBJ.  Then, in
-	 the second call, we can just use the value of RESULTOBJ to do
-	 our job.  */
-      if (resultobj != NULL)
-	Py_DECREF (resultobj);
-
-      resultobj = NULL;
-      if (obj == NULL)
-	error (_("Invalid invocation of Python command object."));
-      if (!PyObject_HasAttr ((PyObject *) obj, complete_cst))
-	{
-	  /* If there is no complete method, don't error.  */
-	  return NULL;
-	}
-
-      textobj = PyUnicode_Decode (text, strlen (text), host_charset (), NULL);
-      if (textobj == NULL)
-	error (_("Could not convert argument to Python string."));
-      wordobj = PyUnicode_Decode (word, sizeof (word), host_charset (), NULL);
-      if (wordobj == NULL)
-	{
-	  Py_DECREF (textobj);
-	  error (_("Could not convert argument to Python string."));
-	}
+      /* If there is no complete method, don't error.  */
+      return NULL;
+    }
 
-      resultobj = PyObject_CallMethodObjArgs ((PyObject *) obj, complete_cst,
-					      textobj, wordobj, NULL);
+  textobj = PyUnicode_Decode (text, strlen (text), host_charset (), NULL);
+  if (textobj == NULL)
+    error (_("Could not convert argument to Python string."));
+  wordobj = PyUnicode_Decode (word, strlen (word), host_charset (), NULL);
+  if (wordobj == NULL)
+    {
       Py_DECREF (textobj);
-      Py_DECREF (wordobj);
-      if (!resultobj)
-	{
-	  /* Just swallow errors here.  */
-	  PyErr_Clear ();
-	}
+      error (_("Could not convert argument to Python string."));
+    }
 
-      Py_XINCREF (resultobj);
+  resultobj = PyObject_CallMethodObjArgs ((PyObject *) obj, complete_cst,
+					  textobj, wordobj, NULL);
+  Py_DECREF (textobj);
+  Py_DECREF (wordobj);
+  if (!resultobj)
+    {
+      /* Just swallow errors here.  */
+      PyErr_Clear ();
     }
 
+  Py_XINCREF (resultobj);
+
   return resultobj;
 }
 
@@ -308,7 +293,7 @@  cmdpy_completer_handle_brkchars (struct cmd_list_element *command,
 
   /* Calling our helper to obtain the PyObject of the Python
      function.  */
-  resultobj = cmdpy_completer_helper (command, text, word, 1);
+  resultobj = cmdpy_completer_helper (command, text, word);
 
   /* Check if there was an error.  */
   if (resultobj == NULL)
@@ -338,8 +323,7 @@  cmdpy_completer_handle_brkchars (struct cmd_list_element *command,
 
  done:
 
-  /* We do not call Py_XDECREF here because RESULTOBJ will be used in
-     the subsequent call to cmdpy_completer function.  */
+  Py_XDECREF (resultobj);
   do_cleanups (cleanup);
 }
 
@@ -357,7 +341,7 @@  cmdpy_completer (struct cmd_list_element *command,
 
   /* Calling our helper to obtain the PyObject of the Python
      function.  */
-  resultobj = cmdpy_completer_helper (command, text, word, 0);
+  resultobj = cmdpy_completer_helper (command, text, word);
 
   /* If the result object of calling the Python function is NULL, it
      means that there was an error.  In this case, just give up and
@@ -419,6 +403,7 @@  cmdpy_completer (struct cmd_list_element *command,
 
  done:
 
+  Py_XDECREF (resultobj);
   do_cleanups (cleanup);
 
   return result;
diff --git a/gdb/testsuite/gdb.python/py-completion.exp b/gdb/testsuite/gdb.python/py-completion.exp
index 0e283e8..5e45087 100644
--- a/gdb/testsuite/gdb.python/py-completion.exp
+++ b/gdb/testsuite/gdb.python/py-completion.exp
@@ -40,7 +40,8 @@  gdb_test_multiple "" "completefileinit completion" {
 }
 
 # Just discarding whatever we typed.
-gdb_test " " ".*" "discard #1"
+set discard 0
+gdb_test " " ".*" "discard #[incr discard]"
 
 # This is the problematic one.
 send_gdb "completefilemethod ${testdir_complete}\t"
@@ -54,7 +55,7 @@  gdb_test_multiple "" "completefilemethod completion" {
 }
 
 # Discarding again
-gdb_test " " ".*" "discard #2"
+gdb_test " " ".*" "discard #[incr discard]"
 
 # Another problematic
 set completion_regex "[string_to_regexp [standard_output_file "py-completion-t"]]"
@@ -67,3 +68,63 @@  gdb_test_multiple "" "completefilecommandcond completion" {
 	pass "completefilecommandcond completion"
     }
 }
+
+# Start gdb over again to clear out current state.  This can interfere
+# with the expected output of the below tests in a buggy gdb.
+gdb_exit
+gdb_start
+gdb_test_no_output "source ${srcdir}/${subdir}/${testfile}.py"
+
+gdb_test_sequence "complete completel" \
+    "list all completions of 'complete completel'" {
+	"completelimit1"
+	"completelimit2"
+	"completelimit3"
+	"completelimit4"
+	"completelimit5"
+	"completelimit6"
+	"completelimit7"
+    }
+
+# Discarding again
+gdb_test " " ".*" "discard #[incr discard]"
+
+gdb_test_sequence "complete completelimit1 c" \
+    "list all completions of 'complete completelimit1 c'" {
+	"completelimit1 cl11"
+	"completelimit1 cl12"
+	"completelimit1 cl13"
+    }
+
+# Discarding again
+gdb_test " " ".*" "discard #[incr discard]"
+
+# If using readline, we can TAB-complete.  This used to trigger a bug
+# because the cached result from the completer was being reused for
+# a different python command.
+if {[readline_is_used]} {
+    set testname "tab-complete 'completelimit1 c'"
+    send_gdb "completelimit1 c\t"
+    gdb_test_multiple "" $testname {
+	-re "^completelimit1 c\\\x07l1$" {
+	    pass $testname
+
+	    # Discard the command line
+	    gdb_test " " ".*" "discard #[incr discard]"
+	}
+    }
+
+    gdb_test_sequence "complete completelimit2 c" \
+	"list all completions of 'complete completelimit2 c'" {
+	    "completelimit2 cl21"
+	    "completelimit2 cl210"
+	    "completelimit2 cl22"
+	    "completelimit2 cl23"
+	    "completelimit2 cl24"
+	    "completelimit2 cl25"
+	    "completelimit2 cl26"
+	    "completelimit2 cl27"
+	    "completelimit2 cl28"
+	    "completelimit2 cl29"
+	}
+}
diff --git a/gdb/testsuite/gdb.python/py-completion.py b/gdb/testsuite/gdb.python/py-completion.py
index e75b6fc..1413c08 100644
--- a/gdb/testsuite/gdb.python/py-completion.py
+++ b/gdb/testsuite/gdb.python/py-completion.py
@@ -53,6 +53,95 @@  class CompleteFileCommandCond(gdb.Command):
 		else:
 			return gdb.COMPLETE_FILENAME
 
+class CompleteLimit1(gdb.Command):
+	def __init__(self):
+		gdb.Command.__init__(self,'completelimit1',gdb.COMMAND_USER)
+
+	def invoke(self,argument,from_tty):
+		raise gdb.GdbError('not implemented')
+
+	def complete(self,text,word):
+                return ["cl11", "cl12", "cl13"]
+
+class CompleteLimit2(gdb.Command):
+	def __init__(self):
+		gdb.Command.__init__(self,'completelimit2',
+                                     gdb.COMMAND_USER)
+
+	def invoke(self,argument,from_tty):
+		raise gdb.GdbError('not implemented')
+
+	def complete(self,text,word):
+		return ["cl21", "cl23", "cl25", "cl27", "cl29",
+                        "cl22", "cl24", "cl26", "cl28", "cl210"]
+
+class CompleteLimit3(gdb.Command):
+	def __init__(self):
+		gdb.Command.__init__(self,'completelimit3',
+                                     gdb.COMMAND_USER)
+
+	def invoke(self,argument,from_tty):
+		raise gdb.GdbError('not implemented')
+
+	def complete(self,text,word):
+		return ["cl31", "cl33", "cl35", "cl37", "cl39",
+                        "cl32", "cl34", "cl36", "cl38", "cl310"]
+
+class CompleteLimit4(gdb.Command):
+	def __init__(self):
+		gdb.Command.__init__(self,'completelimit4',
+                                     gdb.COMMAND_USER)
+
+	def invoke(self,argument,from_tty):
+		raise gdb.GdbError('not implemented')
+
+	def complete(self,text,word):
+		return ["cl41", "cl43", "cl45", "cl47", "cl49",
+                        "cl42", "cl44", "cl46", "cl48", "cl410"]
+
+class CompleteLimit5(gdb.Command):
+	def __init__(self):
+		gdb.Command.__init__(self,'completelimit5',
+                                     gdb.COMMAND_USER)
+
+	def invoke(self,argument,from_tty):
+		raise gdb.GdbError('not implemented')
+
+	def complete(self,text,word):
+		return ["cl51", "cl53", "cl55", "cl57", "cl59",
+                        "cl52", "cl54", "cl56", "cl58", "cl510"]
+
+class CompleteLimit6(gdb.Command):
+	def __init__(self):
+		gdb.Command.__init__(self,'completelimit6',
+                                     gdb.COMMAND_USER)
+
+	def invoke(self,argument,from_tty):
+		raise gdb.GdbError('not implemented')
+
+	def complete(self,text,word):
+		return ["cl61", "cl63", "cl65", "cl67", "cl69",
+                        "cl62", "cl64", "cl66", "cl68", "cl610"]
+
+class CompleteLimit7(gdb.Command):
+	def __init__(self):
+		gdb.Command.__init__(self,'completelimit7',
+                                     gdb.COMMAND_USER)
+
+	def invoke(self,argument,from_tty):
+		raise gdb.GdbError('not implemented')
+
+	def complete(self,text,word):
+		return ["cl71", "cl73", "cl75", "cl77", "cl79",
+                        "cl72", "cl74", "cl76", "cl78", "cl710"]
+
 CompleteFileInit()
 CompleteFileMethod()
 CompleteFileCommandCond()
+CompleteLimit1()
+CompleteLimit2()
+CompleteLimit3()
+CompleteLimit4()
+CompleteLimit5()
+CompleteLimit6()
+CompleteLimit7()