Implement DAP register scope

I noticed that gdb's DAP code did not provide a way to see register
values.  DAP defines a "register" scope, which this patch implements.
This patch also adds the missing (and optional) "presentationHint" to
scopes.

gdb/python/lib/gdb/dap/scopes.py

@@ -50,14 +50,16 @@ def _block_vars(block):
 
 
 class ScopeReference(BaseReference):
-    def __init__(self, name, frame, var_list):
+    def __init__(self, name, hint, frame, var_list):
         super().__init__(name)
+        self.hint = hint
         self.frame = frame
         self.func = frame.function()
         self.var_list = var_list
 
     def to_object(self):
         result = super().to_object()
+        result["presentationHint"] = self.hint
         # How would we know?
         result["expensive"] = False
         result["namedVariables"] = len(self.var_list)
@@ -79,6 +81,17 @@ class ScopeReference(BaseReference):
         return (sym.print_name, val)
 
 
+class RegisterReference(ScopeReference):
+    def __init__(self, name, frame):
+        super().__init__(
+            name, "registers", frame, list(frame.architecture().registers())
+        )
+
+    @in_gdb_thread
+    def fetch_one_child(self, idx):
+        return (self.var_list[idx].name, self.frame.read_register(self.var_list[idx]))
+
+
 # Helper function to create a DAP scopes for a given frame ID.
 @in_gdb_thread
 def _get_scope(id):
@@ -88,9 +101,10 @@ def _get_scope(id):
     if block is not None:
         (args, locs) = _block_vars(block)
         if args:
-            scopes.append(ScopeReference("Arguments", frame, args))
+            scopes.append(ScopeReference("Arguments", "arguments", frame, args))
         if locs:
-            scopes.append(ScopeReference("Locals", frame, locs))
+            scopes.append(ScopeReference("Locals", "locals", frame, locs))
+    scopes.append(RegisterReference("Registers", frame))
     return [x.to_object() for x in scopes]
 
 

gdb/testsuite/gdb.dap/scopes.exp

@@ -52,12 +52,20 @@ set scopes [dap_check_request_and_response "get scopes" scopes \
 		[format {o frameId [i %d]} $frame_id]]
 set scopes [dict get [lindex $scopes 0] body scopes]
 
-gdb_assert {[llength $scopes] == 1} "single scope"
+gdb_assert {[llength $scopes] == 2} "two scopes"
 
-set scope [lindex $scopes 0]
+lassign $scopes scope reg_scope
 gdb_assert {[dict get $scope name] == "Locals"} "scope is locals"
+gdb_assert {[dict get $scope presentationHint] == "locals"} \
+    "locals presentation hint"
 gdb_assert {[dict get $scope namedVariables] == 3} "three vars in scope"
 
+gdb_assert {[dict get $reg_scope name] == "Registers"} \
+    "second scope is registers"
+gdb_assert {[dict get $reg_scope presentationHint] == "registers"} \
+    "registers presentation hint"
+gdb_assert {[dict get $reg_scope namedVariables] > 0} "at least one register"
+
 set num [dict get $scope variablesReference]
 set refs [lindex [dap_check_request_and_response "fetch variables" \
 		      "variables" \
@@ -98,4 +106,10 @@ set refs [lindex [dap_check_request_and_response "fetch contents of dei" \
 set deivals [dict get $refs body variables]
 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]
+
 dap_shutdown