gdb: error if 'thread' or 'task' keywords are overused

When creating a breakpoint or watchpoint, the 'thread' and 'task'
keywords can be used to create a thread or task specific breakpoint or
watchpoint.

Currently, a thread or task specific breakpoint can only apply for a
single thread or task, if multiple threads or tasks are specified when
creating the breakpoint (or watchpoint), then the last specified id
will be used.

The exception to the above is that when the 'thread' keyword is used
during the creation of a watchpoint, GDB will give an error if
'thread' is given more than once.

In this commit I propose making this behaviour consistent, if the
'thread' or 'task' keywords are used more than once when creating
either a breakpoint or watchpoint, then GDB will give an error.

I haven't updated the manual, we don't explicitly say that these
keywords can be repeated, and (to me), given the keyword takes a
single id, I don't think it makes much sense to repeat the keyword.
As such, I see this more as adding a missing error to GDB, rather than
making some big change.  However, I have added an entry to the NEWS
file as I guess it is possible that some people might hit this new
error with an existing (I claim, badly written) GDB script.

I've added some new tests to check for the new error.

Just one test needed updating, gdb.linespec/keywords.exp, this test
did use the 'thread' keyword twice, and expected the breakpoint to be
created.  Looking at what this test was for though, it was checking
the use of '-force-condition', and I don't think that being able to
repeat 'thread' was actually a critical part of this test.

As such, I've updated this test to expect the error when 'thread' is
repeated.

1 files changed, 14 insertions, 0 deletions

diff --git a/gdb/NEWS b/gdb/NEWS
index 882ea4c..1567cbe 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -30,6 +30,20 @@
   This support requires that GDB be built with Python scripting
   enabled.
 
+* For the break command, multiple uses of the 'thread' or 'task'
+  keywords will now give an error instead of just using the thread or
+  task id from the last instance of the keyword.  E.g.:
+    break foo thread 1 thread 2
+  will now give an error rather than using 'thread 2'.
+
+* For the watch command, multiple uses of the 'task' keyword will now
+  give an error instead of just using the task id from the last
+  instance of the keyword.  E.g.:
+    watch my_var task 1 task 2
+  will now give an error rather than using 'task 2'.  The 'thread'
+  keyword already gave an error when used multiple times with the
+  watch command, this remains unchanged.
+
 * New commands
 
 maintenance print record-instruction [ N ]