Re: [PATCH] Eliminate UNSUPPORTED_ERROR.

[Pedro Alves <palves at redhat dot com>]

On 12/12/2013 04:22 AM, Doug Evans wrote:
> On Wed, Dec 11, 2013 at 11:17 AM, Pedro Alves <palves@redhat.com> wrote:
>> On 12/11/2013 04:33 PM, Doug Evans wrote:
>>>>> -         /* Should we fallback to ye olde GDB script mode?  */
>>>>> -         if (script_ext_mode == script_ext_soft
>>>>> -             && e.reason == RETURN_ERROR && e.error == UNSUPPORTED_ERROR)
>>>>> -           {
>>>>> -             fseek (stream, 0, SEEK_SET);
>>>>> -             script_from_file (stream, (char*) file);
>>>>> -           }
>>>>> -         else
>>>>> -           {
>>>>> -             /* Nope, just punt.  */
>>>>> -             throw_exception (e);
>>>>> -           }
>>>>> +         /* Fallback to GDB script mode.  */
>>>>> +         fseek (stream, 0, SEEK_SET);
>>>>> +         script_from_file (stream, (char*) file);
>>> Remove the fseek and cast.
>>
>> Hmm, indeed the fseek doesn't look necessary.  Will do.  However,
>> that makes me wonder whether I'm missing something, as it doesn't
>> look necessary before my patch either.  Was it ever really
>> needed?
> 
> I think I added it to be extra conservative in case
> source_python_script happened to read from the file.
> [I know it normally wouldn't read and then throw an UNSUPPORTED_ERROR,
> but I'm guessing I didn't want this code to assume that.]
> 
> Now that we're not even calling source_python_script the need is gone.
> 
>  I see you added it (and the unnecessary cast too ;-) ) in:
>>   https://www.sourceware.org/ml/gdb-patches/2010-04/msg00110.html
>> but I can't tell why.
> 
> script_from_file was changed to take a const char *arg the prior week.
> Presumably I just didn't update that part of the patch.
> 

Alright, pushed, as below.
--------
Eliminate UNSUPPORTED_ERROR.

I have a case that could use an exception for "unsupported feature".
I found UNSUPPORTED_ERROR, but looking deeper, I think as is, reusing
it for other things would be fragile.  E.g., if the Python script
sourced by source_script_from_stream triggers any other missing
functionality that would result in UNSUPPORTED_ERROR being propagated
out to source_script_from_stream, that would confuse the error for
Python not being built into GDB.

This patch thus redoes things a little.  Instead of using an exception
for the "No Python" scenario, check whether Python is configured in
before actually trying to source the file.  It adds a new function
instead of using #ifdef HAVE_PYTHON directly, as that is better at
avoiding bitrot, as both Python and !Python paths are visible to the
compiler this way.

Tested on Fedora 17, with and without Python.

gdb/
2013-12-12  Pedro Alves  <palves@redhat.com>

	* cli/cli-cmds.c (source_script_from_stream) Use have_python
	instead of catching UNSUPPORTED_ERROR.
	* exceptions.h (UNSUPPORTED_ERROR): Delete.
	* python/python.c (source_python_script) [!HAVE_PYTHON]: Internal
	error if called.
	* python/python.h (have_python): New static inline function.
---
 gdb/ChangeLog       |  9 +++++++++
 gdb/cli/cli-cmds.c  | 26 +++++++-------------------
 gdb/exceptions.h    |  3 ---
 gdb/python/python.c |  5 +++--
 gdb/python/python.h | 13 +++++++++++++
 5 files changed, 32 insertions(+), 24 deletions(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 40368b5..637a462 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,12 @@
+2013-12-12  Pedro Alves  <palves@redhat.com>
+
+	* cli/cli-cmds.c (source_script_from_stream) Use have_python
+	instead of catching UNSUPPORTED_ERROR.
+	* exceptions.h (UNSUPPORTED_ERROR): Delete.
+	* python/python.c (source_python_script) [!HAVE_PYTHON]: Internal
+	error if called.
+	* python/python.h (have_python): New static inline function.
+
 2013-12-11  Doug Evans  <dje@google.com>
 
 	* dwarf2read.c (lookup_dwo_cutu): Include name of dwp file in
diff --git a/gdb/cli/cli-cmds.c b/gdb/cli/cli-cmds.c
index 52a6bc9..73e03cf 100644
--- a/gdb/cli/cli-cmds.c
+++ b/gdb/cli/cli-cmds.c
@@ -525,27 +525,15 @@ source_script_from_stream (FILE *stream, const char *file)
   if (script_ext_mode != script_ext_off
       && strlen (file) > 3 && !strcmp (&file[strlen (file) - 3], ".py"))
     {
-      volatile struct gdb_exception e;
-
-      TRY_CATCH (e, RETURN_MASK_ERROR)
+      if (have_python ())
+	source_python_script (stream, file);
+      else if (script_ext_mode == script_ext_soft)
 	{
-	  source_python_script (stream, file);
-	}
-      if (e.reason < 0)
-	{
-	  /* Should we fallback to ye olde GDB script mode?  */
-	  if (script_ext_mode == script_ext_soft
-	      && e.reason == RETURN_ERROR && e.error == UNSUPPORTED_ERROR)
-	    {
-	      fseek (stream, 0, SEEK_SET);
-	      script_from_file (stream, (char*) file);
-	    }
-	  else
-	    {
-	      /* Nope, just punt.  */
-	      throw_exception (e);
-	    }
+	  /* Fallback to GDB script mode.  */
+	  script_from_file (stream, file);
 	}
+      else
+	error (_("Python scripting is not supported in this copy of GDB."));
     }
   else
     script_from_file (stream, file);
diff --git a/gdb/exceptions.h b/gdb/exceptions.h
index 705f1a1..2cb8242 100644
--- a/gdb/exceptions.h
+++ b/gdb/exceptions.h
@@ -79,9 +79,6 @@ enum errors {
   /* Error accessing memory.  */
   MEMORY_ERROR,
 
-  /* Feature is not supported in this copy of GDB.  */
-  UNSUPPORTED_ERROR,
-
   /* Value not available.  E.g., a register was not collected in a
      traceframe.  */
   NOT_AVAILABLE_ERROR,
diff --git a/gdb/python/python.c b/gdb/python/python.c
index 1873936..55bb6cf 100644
--- a/gdb/python/python.c
+++ b/gdb/python/python.c
@@ -1390,8 +1390,9 @@ eval_python_from_control_command (struct command_line *cmd)
 void
 source_python_script (FILE *file, const char *filename)
 {
-  throw_error (UNSUPPORTED_ERROR,
-	       _("Python scripting is not supported in this copy of GDB."));
+  internal_error (__FILE__, __LINE__,
+		  _("source_python_script called when Python scripting is "
+		    "not supported."));
 }
 
 int
diff --git a/gdb/python/python.h b/gdb/python/python.h
index c07b2aa..abbb581 100644
--- a/gdb/python/python.h
+++ b/gdb/python/python.h
@@ -89,6 +89,19 @@ typedef enum py_frame_args
   CLI_ALL_VALUES
 } py_frame_args;
 
+/* Returns true if Python support is built into GDB, false
+   otherwise.  */
+
+static inline int
+have_python (void)
+{
+#ifdef HAVE_PYTHON
+  return 1;
+#else
+  return 0;
+#endif
+}
+
 extern void finish_python_initialization (void);
 
 void eval_python_from_control_command (struct command_line *);
-- 
1.7.11.7