gdb/mi: handle no condition argument case for -break-condition

As reported in PR gdb/28076 [1], passing no condition argument to the
-break-condition command (e.g.: "-break-condition 2") should clear the
condition for breakpoint 2, just like CLI's "condition 2", but instead
an error message is returned:

  ^error,msg="-break-condition: Missing the <number> and/or <expr> argument"

The current implementation of the -break-condition command's argument
handling (79aabb7308c "gdb/mi: add a '--force' flag to the
'-break-condition' command") was done according to the documentation,
where the condition argument seemed mandatory.  However, the
-break-condition command originally (i.e. before the 79aabb7308c
patch) used the CLI's "cond" command, and back then not passing a
condition argument was clearing out the condition.  So, this is a
regression in terms of the behavior.

Fix the argument handling of the -break-condition command to allow not
having a condition argument, and also update the document to make the
behavior clear.  Also add test cases to test the scenarios which were
previously not covered.

[1] https://sourceware.org/bugzilla/show_bug.cgi?id=28076

1 files changed, 7 insertions, 8 deletions

diff --git a/gdb/mi/mi-cmd-break.c b/gdb/mi/mi-cmd-break.c
index 5439937..c2d642d 100644
--- a/gdb/mi/mi-cmd-break.c
+++ b/gdb/mi/mi-cmd-break.c
@@ -423,20 +423,19 @@ mi_cmd_break_condition (const char *command, char **argv, int argc)
 	}
     }
 
-  /* There must be at least two more args: a bpnum and a condition
-     expression.  */
-  if (oind + 1 >= argc)
-    error (_("-break-condition: Missing the <number> and/or <expr> "
-	     "argument"));
+  /* There must be at least one more arg: a bpnum.  */
+  if (oind >= argc)
+    error (_("-break-condition: Missing the <number> argument"));
 
   int bpnum = atoi (argv[oind]);
 
   /* The rest form the condition expr.  */
-  std::string expr (argv[oind + 1]);
-  for (int i = oind + 2; i < argc; ++i)
+  std::string expr = "";
+  for (int i = oind + 1; i < argc; ++i)
     {
-      expr += " ";
       expr += argv[i];
+      if (i + 1 < argc)
+	expr += " ";
     }
 
   set_breakpoint_condition (bpnum, expr.c_str (), 0 /* from_tty */,