Re: [pushed] gdb/mi: consistently notify user when GDB/MI client uses -thread-select

[Simon Marchi <simon.marchi@polymtl.ca>]

> Just tried on Ubuntu 20.04 and I do not any problem. 

I'm trying to look a bit more into it.  The state is that we have thread
2 already selected, issue a `-thread-select 2` on the MI UI, and expect
to not have a CLI notification to say that the thread changed, since we
try to select the already selected thread.

Before your patch I get:

    -thread-select 2

    ^done,new-thread-id="2",frame={level="0",addr="0x00005555555551b8",func="child_sub_function",args=[],file="/home/smarchi/src/binutils-gdb/gdb/testsuite/gdb.mi/user-selected-context-sync.c",fullname="/home/smarchi/src/binutils-gdb/gdb/testsuite/gdb.mi/user-selected-context-sync.c",line="33",arch="i386:x86-64"}

    (gdb) 

    PASS: gdb.mi/user-selected-context-sync.exp: mode=all-stop: test_mi_thread_select: thread 1.2: -thread-select again
    print 666

    $9 = 666

    (gdb) PASS: gdb.mi/user-selected-context-sync.exp: mode=all-stop: test_mi_thread_select: thread 1.2: -thread-select again, event on CLI, ensure no output CLI

After:

    -thread-select 2

    ^done,new-thread-id="2",frame={level="0",addr="0x00005555555551b8",func="child_sub_function",args=[],file="/home/smarchi/src/binutils-gdb/gdb/testsuite/gdb.mi/user-selected-context-sync.c",fullname="/home/smarchi/src/binutils-gdb/gdb/testsuite/gdb.mi/user-selected-context-sync.c",line="33",arch="i386:x86-64"}

    (gdb) 

    PASS: gdb.mi/user-selected-context-sync.exp: mode=all-stop: test_mi_thread_select: thread 1.2: -thread-select again
    [Switching to thread 1.2 (Thread 0x7ffff7d99700 (LWP 1885257))]

    #0  child_sub_function () at /home/smarchi/src/binutils-gdb/gdb/testsuite/gdb.mi/user-selected-context-sync.c:33

    33	    dummy = !dummy; /* thread loop line */

    print 666

    $9 = 666

    (gdb) FAIL: gdb.mi/user-selected-context-sync.exp: mode=all-stop: test_mi_thread_select: thread 1.2: -thread-select again, event on CLI, ensure no output CLI

So there is really a spurious "Switching to thread 1.2" notification in
my case.

Trying a simpler case, just an empty main program, I do this (/dev/pts/8
being the tty for my MI UI):

    $ ./gdb -q -nx --data-directory=data-directory a.out -ex "new-ui mi /dev/pts/8" -ex start

If I then type `-thread-select 1` on the MI UI, I do get:

    [Switching to thread 1 (process 1891548)]

... which is unexpected.  Before your patch, I don't get it.  Can you
give this small test a try?

Simon