[gdb] Make execute_command_to_string return string on throw

The pattern for using execute_command_to_string is:
...
  std::string output;
  output = execute_fn_to_string (fn, term_out);
...

This results in a problem when using it in a try/catch:
...
  try
    {
      output = execute_fn_to_string (fn, term_out)
    }
  catch (const gdb_exception &e)
    {
      /* Use output.  */
    }
...

If an expection was thrown during execute_fn_to_string, then the output
remains unassigned, while it could be worthwhile to known what output was
generated by gdb before the expection was thrown.

Fix this by returning the string using a parameter instead:
...
  execute_fn_to_string (output, fn, term_out)
...

Also add a variant without string parameter, to support places where the
function is used while ignoring the result:
...
  execute_fn_to_string (fn, term_out)
...

Tested on x86_64-linux.

1 files changed, 30 insertions, 7 deletions

diff --git a/gdb/top.c b/gdb/top.c
index 08cdb48..1f9e649 100644
--- a/gdb/top.c
+++ b/gdb/top.c
@@ -724,13 +724,25 @@ execute_fn_to_ui_file (struct ui_file *file, std::function<void(void)> fn)
 
 /* See gdbcmd.h.  */
 
-std::string
-execute_fn_to_string (std::function<void(void)> fn, bool term_out)
+void
+execute_fn_to_string (std::string &res, std::function<void(void)> fn,
+		      bool term_out)
 {
   string_file str_file (term_out);
 
-  execute_fn_to_ui_file (&str_file, fn);
-  return std::move (str_file.string ());
+  try
+    {
+      execute_fn_to_ui_file (&str_file, fn);
+    }
+  catch (...)
+    {
+      /* Finally.  */
+      res = std::move (str_file.string ());
+      throw;
+    }
+
+  /* And finally.  */
+  res = std::move (str_file.string ());
 }
 
 /* See gdbcmd.h.  */
@@ -744,12 +756,23 @@ execute_command_to_ui_file (struct ui_file *file,
 
 /* See gdbcmd.h.  */
 
-std::string
+void
+execute_command_to_string (std::string &res, const char *p, int from_tty,
+			   bool term_out)
+{
+  execute_fn_to_string (res, [=]() { execute_command (p, from_tty); },
+			term_out);
+}
+
+/* See gdbcmd.h.  */
+
+void
 execute_command_to_string (const char *p, int from_tty,
 			   bool term_out)
 {
-  return
-    execute_fn_to_string ([=]() { execute_command (p, from_tty); }, term_out);
+  std::string dummy;
+  execute_fn_to_string (dummy, [=]() { execute_command (p, from_tty); },
+			term_out);
 }
 
 /* When nonzero, cause dont_repeat to do nothing.  This should only be