[binutils-gdb] Simplify interp::exec / interp_exec - let exceptions propagate

[binutils-gdb] Simplify interp::exec / interp_exec - let exceptions propagate

[Pedro Alves]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=b885aea1bb987435929b4298982ac6fc27f69403

commit b885aea1bb987435929b4298982ac6fc27f69403
Author: Pedro Alves <pedro@palves.net>
Date:   Fri Jan 27 18:07:56 2023 +0000

    Simplify interp::exec / interp_exec - let exceptions propagate
    
    This patch implements a simplication that I suggested here:
    
      https://sourceware.org/pipermail/gdb-patches/2022-March/186320.html
    
    Currently, the interp::exec virtual method interface is such that
    subclass implementations must catch exceptions and then return them
    via normal function return.
    
    However, higher up the in chain, for the CLI we get to
    interpreter_exec_cmd, which does:
    
      for (i = 1; i < nrules; i++)
        {
          struct gdb_exception e = interp_exec (interp_to_use, prules[i]);
    
          if (e.reason < 0)
            {
              interp_set (old_interp, 0);
              error (_("error in command: \"%s\"."), prules[i]);
            }
        }
    
    and for MI we get to mi_cmd_interpreter_exec, which has:
    
      void
      mi_cmd_interpreter_exec (const char *command, char **argv, int argc)
      {
      ...
        for (i = 1; i < argc; i++)
          {
            struct gdb_exception e = interp_exec (interp_to_use, argv[i]);
    
            if (e.reason < 0)
              error ("%s", e.what ());
          }
      }
    
    Note that if those errors are reached, we lose the original
    exception's error code.  I can't see why we'd want that.
    
    And, I can't see why we need to have interp_exec catch the exception
    and return it via the normal return path.  That's normally needed when
    we need to handle propagating exceptions across C code, like across
    readline or ncurses, but that's not the case here.
    
    It seems to me that we can simplify things by removing some
    try/catch-ing and just letting exceptions propagate normally.
    
    Note, the "error in command" error shown above, which only exists in
    the CLI interpreter-exec command, is only ever printed AFAICS if you
    run "interpreter-exec console" when the top level interpreter is
    already the console/tui.  Like:
    
     (gdb) interpreter-exec console "foobar"
     Undefined command: "foobar".  Try "help".
     error in command: "foobar".
    
    You won't see it with MI's "-interpreter-exec console" from a top
    level MI interpreter:
    
     (gdb)
     -interpreter-exec console "foobar"
     &"Undefined command: \"foobar\".  Try \"help\".\n"
     ^error,msg="Undefined command: \"foobar\".  Try \"help\"."
     (gdb)
    
    nor with MI's "-interpreter-exec mi" from a top level MI interpreter:
    
     (gdb)
     -interpreter-exec mi "-foobar"
     ^error,msg="Undefined MI command: foobar",code="undefined-command"
     ^done
     (gdb)
    
    in both these cases because MI's -interpreter-exec just does:
    
      error ("%s", e.what ());
    
    You won't see it either when running an MI command with the CLI's
    "interpreter-exec mi":
    
     (gdb) interpreter-exec mi "-foobar"
     ^error,msg="Undefined MI command: foobar",code="undefined-command"
     (gdb)
    
    This last case is because MI's interp::exec implementation never
    returns an error:
    
     gdb_exception
     mi_interp::exec (const char *command)
     {
       mi_execute_command_wrapper (command);
       return gdb_exception ();
     }
    
    Thus I think that "error in command" error is pretty pointless, and
    since it simplifies things to not have it, the patch just removes it.
    
    The patch also ends up addressing an old FIXME.
    
    Change-Id: I5a6432a80496934ac7127594c53bf5221622e393
    Approved-By: Tom Tromey <tromey@adacore.com>
    Approved-By: Kevin Buettner <kevinb@redhat.com>

Diff:
---
 gdb/cli/cli-interp.c | 49 ++++++++++++++-----------------------------------
 gdb/interps.c        | 21 ++++++++-------------
 gdb/interps.h        |  5 ++---
 gdb/mi/mi-interp.c   | 10 ++--------
 gdb/mi/mi-interp.h   |  2 +-
 gdb/python/py-dap.c  |  3 +--
 gdb/tui/tui-interp.c |  4 ++--
 7 files changed, 30 insertions(+), 64 deletions(-)

diff --git a/gdb/cli/cli-interp.c b/gdb/cli/cli-interp.c
index 5f2ff726f26..99410147a6c 100644
--- a/gdb/cli/cli-interp.c
+++ b/gdb/cli/cli-interp.c
@@ -48,7 +48,7 @@ class cli_interp final : public cli_interp_base
   void init (bool top_level) override;
   void resume () override;
   void suspend () override;
-  gdb_exception exec (const char *command_str) override;
+  void exec (const char *command_str) override;
   ui_out *interp_ui_out () override;
 
 private:
@@ -75,11 +75,6 @@ as_cli_interp_base (interp *interp)
   return dynamic_cast<cli_interp_base *> (interp);
 }
 
-/* Longjmp-safe wrapper for "execute_command".  */
-static struct gdb_exception safe_execute_command (struct ui_out *uiout,
-						  const char *command, 
-						  int from_tty);
-
 /* See cli-interp.h.
 
    Breakpoint hits should always be mirrored to a console.  Deciding
@@ -314,12 +309,9 @@ cli_interp::suspend ()
   gdb_disable_readline ();
 }
 
-gdb_exception
+void
 cli_interp::exec (const char *command_str)
 {
-  struct ui_file *old_stream;
-  struct gdb_exception result;
-
   /* gdb_stdout could change between the time m_cli_uiout was
      initialized and now.  Since we're probably using a different
      interpreter which has a new ui_file for gdb_stdout, use that one
@@ -327,41 +319,28 @@ cli_interp::exec (const char *command_str)
 
      It is important that it gets reset everytime, since the user
      could set gdb to use a different interpreter.  */
-  old_stream = m_cli_uiout->set_stream (gdb_stdout);
-  result = safe_execute_command (m_cli_uiout.get (), command_str, 1);
-  m_cli_uiout->set_stream (old_stream);
-  return result;
-}
-
-bool
-cli_interp_base::supports_command_editing ()
-{
-  return true;
-}
-
-static struct gdb_exception
-safe_execute_command (struct ui_out *command_uiout, const char *command,
-		      int from_tty)
-{
-  struct gdb_exception e;
+  ui_file *old_stream = m_cli_uiout->set_stream (gdb_stdout);
+  SCOPE_EXIT { m_cli_uiout->set_stream (old_stream); };
 
   /* Save and override the global ``struct ui_out'' builder.  */
   scoped_restore saved_uiout = make_scoped_restore (&current_uiout,
-						    command_uiout);
+						    m_cli_uiout.get ());
 
   try
     {
-      execute_command (command, from_tty);
+      execute_command (command_str, 1);
     }
-  catch (gdb_exception &exception)
+  catch (const gdb_exception_error &ex)
     {
-      e = std::move (exception);
+      exception_print (gdb_stderr, ex);
+      throw;
     }
+}
 
-  /* FIXME: cagney/2005-01-13: This shouldn't be needed.  Instead the
-     caller should print the exception.  */
-  exception_print (gdb_stderr, e);
-  return e;
+bool
+cli_interp_base::supports_command_editing ()
+{
+  return true;
 }
 
 ui_out *
diff --git a/gdb/interps.c b/gdb/interps.c
index 24dc616fc1a..9c7908bde1c 100644
--- a/gdb/interps.c
+++ b/gdb/interps.c
@@ -39,6 +39,7 @@
 #include "top.h"		/* For command_loop.  */
 #include "main.h"
 #include "gdbsupport/buildargv.h"
+#include "gdbsupport/scope-exit.h"
 
 /* Each UI has its own independent set of interpreters.  */
 
@@ -332,7 +333,7 @@ interp_supports_command_editing (struct interp *interp)
 /* interp_exec - This executes COMMAND_STR in the current 
    interpreter.  */
 
-struct gdb_exception
+void
 interp_exec (struct interp *interp, const char *command_str)
 {
   struct ui_interp_info *ui_interp = get_current_interp_info ();
@@ -341,7 +342,7 @@ interp_exec (struct interp *interp, const char *command_str)
   scoped_restore save_command_interp
     = make_scoped_restore (&ui_interp->command_interpreter, interp);
 
-  return interp->exec (command_str);
+  interp->exec (command_str);
 }
 
 /* A convenience routine that nulls out all the common command hooks.
@@ -393,19 +394,13 @@ interpreter_exec_cmd (const char *args, int from_tty)
     error (_("Could not find interpreter \"%s\"."), prules[0]);
 
   interp_set (interp_to_use, false);
-
-  for (i = 1; i < nrules; i++)
+  SCOPE_EXIT
     {
-      struct gdb_exception e = interp_exec (interp_to_use, prules[i]);
-
-      if (e.reason < 0)
-	{
-	  interp_set (old_interp, 0);
-	  error (_("error in command: \"%s\"."), prules[i]);
-	}
-    }
+      interp_set (old_interp, false);
+    };
 
-  interp_set (old_interp, 0);
+  for (i = 1; i < nrules; i++)
+    interp_exec (interp_to_use, prules[i]);
 }
 
 /* See interps.h.  */
diff --git a/gdb/interps.h b/gdb/interps.h
index 2caa7bf9fee..01bec47550d 100644
--- a/gdb/interps.h
+++ b/gdb/interps.h
@@ -36,8 +36,7 @@ typedef struct interp *(*interp_factory_func) (const char *name);
 extern void interp_factory_register (const char *name,
 				     interp_factory_func func);
 
-extern struct gdb_exception interp_exec (struct interp *interp,
-					 const char *command);
+extern void interp_exec (struct interp *interp, const char *command);
 
 class interp
 {
@@ -51,7 +50,7 @@ public:
   virtual void resume () = 0;
   virtual void suspend () = 0;
 
-  virtual gdb_exception exec (const char *command) = 0;
+  virtual void exec (const char *command) = 0;
 
   /* Returns the ui_out currently used to collect results for this
      interpreter.  It can be a formatter for stdout, as is the case
diff --git a/gdb/mi/mi-interp.c b/gdb/mi/mi-interp.c
index cf3d738edce..29d1aee8235 100644
--- a/gdb/mi/mi-interp.c
+++ b/gdb/mi/mi-interp.c
@@ -199,11 +199,10 @@ mi_interp::suspend ()
   gdb_disable_readline ();
 }
 
-gdb_exception
+void
 mi_interp::exec (const char *command)
 {
   mi_execute_command_wrapper (command);
-  return gdb_exception ();
 }
 
 void
@@ -240,12 +239,7 @@ mi_cmd_interpreter_exec (const char *command, char **argv, int argc)
     };
 
   for (i = 1; i < argc; i++)
-    {
-      struct gdb_exception e = interp_exec (interp_to_use, argv[i]);
-
-      if (e.reason < 0)
-	error ("%s", e.what ());
-    }
+    interp_exec (interp_to_use, argv[i]);
 }
 
 /* This inserts a number of hooks that are meant to produce
diff --git a/gdb/mi/mi-interp.h b/gdb/mi/mi-interp.h
index 827297f02e2..e07be12f87a 100644
--- a/gdb/mi/mi-interp.h
+++ b/gdb/mi/mi-interp.h
@@ -36,7 +36,7 @@ public:
   void init (bool top_level) override;
   void resume () override;
   void suspend () override;
-  gdb_exception exec (const char *command_str) override;
+  void exec (const char *command_str) override;
   ui_out *interp_ui_out () override;
   void set_logging (ui_file_up logfile, bool logging_redirect,
 		    bool debug_redirect) override;
diff --git a/gdb/python/py-dap.c b/gdb/python/py-dap.c
index 9c77b2a4f76..32f927214d7 100644
--- a/gdb/python/py-dap.c
+++ b/gdb/python/py-dap.c
@@ -45,10 +45,9 @@ public:
   {
   }
 
-  gdb_exception exec (const char *command) override
+  void exec (const char *command) override
   {
     /* Just ignore it.  */
-    return {};
   }
 
   void set_logging (ui_file_up logfile, bool logging_redirect,
diff --git a/gdb/tui/tui-interp.c b/gdb/tui/tui-interp.c
index 3c28145d996..812c62c6422 100644
--- a/gdb/tui/tui-interp.c
+++ b/gdb/tui/tui-interp.c
@@ -49,7 +49,7 @@ public:
   void init (bool top_level) override;
   void resume () override;
   void suspend () override;
-  gdb_exception exec (const char *command_str) override;
+  void exec (const char *command_str) override;
   ui_out *interp_ui_out () override;
 };
 
@@ -149,7 +149,7 @@ tui_interp::interp_ui_out ()
     return tui_old_uiout;
 }
 
-gdb_exception
+void
 tui_interp::exec (const char *command_str)
 {
   internal_error (_("tui_exec called"));