[binutils-gdb/gdb-14-branch] Fix register-setting response from DAP

[Tom Tromey]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=8836926927c8f712131ec2d3c03bdf885dbe33d1

commit 8836926927c8f712131ec2d3c03bdf885dbe33d1
Author: Tom Tromey <tromey@adacore.com>
Date:   Wed Oct 4 12:58:32 2023 -0600

    Fix register-setting response from DAP
    
    Andry noticed that given a DAP setExpression request, where the
    expression to set is a register, DAP will return the wrong value -- it
    will return the old value, not the updated one.
    
    This happens because gdb.Value.assign (which was recently added for
    DAP) does not update the value.
    
    In this patch, I chose to have the assign method update the Value
    in-place.  It's also possible to have it return a new value, but this
    didn't seem very useful to me.

Diff:
---
 gdb/python/py-value.c            |  8 +++++++-
 gdb/testsuite/gdb.dap/scopes.exp | 25 ++++++++++++++++++++++---
 2 files changed, 29 insertions(+), 4 deletions(-)

diff --git a/gdb/python/py-value.c b/gdb/python/py-value.c
index 245de68e0b9..0bf1d6e0dae 100644
--- a/gdb/python/py-value.c
+++ b/gdb/python/py-value.c
@@ -905,7 +905,13 @@ valpy_assign (PyObject *self_obj, PyObject *args)
   try
     {
       value_object *self = (value_object *) self_obj;
-      value_assign (self->value, val);
+      value *new_value = value_assign (self->value, val);
+      /* value_as_address returns a new value with the same location
+	 as the old one.  Ensure that this gdb.Value is updated to
+	 reflect the new value.  */
+      new_value->incref ();
+      self->value->decref ();
+      self->value = new_value;
     }
   catch (const gdb_exception &except)
     {
diff --git a/gdb/testsuite/gdb.dap/scopes.exp b/gdb/testsuite/gdb.dap/scopes.exp
index 003557cf323..db815d2d5aa 100644
--- a/gdb/testsuite/gdb.dap/scopes.exp
+++ b/gdb/testsuite/gdb.dap/scopes.exp
@@ -125,8 +125,27 @@ gdb_assert {[llength $deivals] == 2} "dei has two members"
 
 set num [dict get $reg_scope variablesReference]
 # The request succeeding is sufficient.
-dap_check_request_and_response "fetch first register" \
-    "variables" \
-    [format {o variablesReference [i %d] count [i 1]} $num]
+set val [dap_check_request_and_response "fetch first register" \
+	     "variables" \
+	     [format {o variablesReference [i %d] count [i 1]} $num]]
+
+# Try setting the value to something else.
+set val [dict get [lindex $val 0] body variables]
+set name [dict get [lindex $val 0] name]
+set val [dict get [lindex $val 0] value]
+# Just make sure it is different from the original value.
+set val [expr {$val ^ 7}]
+
+# setVariable isn't implemented yet, so use the register name.  Note
+# that we sneak the "$" into the name, written in a slightly funny way
+# to work around apparent TON limitations.
+set response [dap_check_request_and_response "set first register" \
+		  setExpression \
+		  [format {o expression [s \$%s] value [s %d] frameId [i %d]} \
+		       $name $val $frame_id]]
+set response [lindex $response 0]
+
+gdb_assert {[dict get $response body value] == $val} \
+    "setting register yields updated value"
 
 dap_shutdown