Respect supportsMemoryReferences in DAP

I noticed that the support for memoryReference in the "variables"
output is gated on the client "supportsMemoryReferences" capability.

This patch implements this and makes some other changes to the DAP
memory reference code:

* Remove the memoryReference special case from _SetResult.
  Upstream DAP fixed this oversight in response to
  https://github.com/microsoft/debug-adapter-protocol/issues/414

* Don't use the address of a variable as its memoryReference -- only
  emit this for pointer types.  There's no spec support for the
  previous approach.

* Use strip_typedefs to handle typedefs of pointers.

gdb/python/lib/gdb/dap/evaluate.py

diff --git a/gdb/python/lib/gdb/dap/evaluate.py b/gdb/python/lib/gdb/dap/evaluate.py
index 63e8033..9fa94e0 100644
--- a/gdb/python/lib/gdb/dap/evaluate.py
+++ b/gdb/python/lib/gdb/dap/evaluate.py
@@ -55,13 +55,6 @@
     def __init__(self, value):
         super().__init__(None, value, "value")
 
-    def to_object(self):
-        result = super().to_object()
-        # This is not specified in the setExpression result.
-        if "memoryReference" in result:
-            del result["memoryReference"]
-        return result
-
 
 # Helper function to perform an assignment.
 @in_gdb_thread

gdb/python/lib/gdb/dap/varref.py

diff --git a/gdb/python/lib/gdb/dap/varref.py b/gdb/python/lib/gdb/dap/varref.py
index 213151f..0e0d92a 100644
--- a/gdb/python/lib/gdb/dap/varref.py
+++ b/gdb/python/lib/gdb/dap/varref.py
@@ -162,10 +162,13 @@
                 result["indexedVariables"] = num_children
             else:
                 result["namedVariables"] = num_children
-        if self.value.type.code == gdb.TYPE_CODE_PTR:
-            result["memoryReference"] = hex(int(self.value))
-        elif self.value.address is not None:
-            result["memoryReference"] = hex(int(self.value.address))
+        if client_bool_capability("supportsMemoryReferences"):
+            # https://github.com/microsoft/debug-adapter-protocol/issues/414
+            # changed DAP to allow memory references for any of the
+            # variable response requests, and to lift the restriction
+            # to pointer-to-function from Variable.
+            if self.value.type.strip_typedefs().code == gdb.TYPE_CODE_PTR:
+                result["memoryReference"] = hex(int(self.value))
         if client_bool_capability("supportsVariableType"):
             result["type"] = str(self.value.type)
         return result

gdb/testsuite/gdb.dap/memory.c

diff --git a/gdb/testsuite/gdb.dap/memory.c b/gdb/testsuite/gdb.dap/memory.c
index 3b9f613..630e23d 100644
--- a/gdb/testsuite/gdb.dap/memory.c
+++ b/gdb/testsuite/gdb.dap/memory.c
@@ -19,6 +19,8 @@
 
 uint32_t thirty_two = 7;
 
+uint32_t *thirty_two_p = &thirty_two;
+
 int main ()
 {
   return 0;			/* BREAK */

gdb/testsuite/gdb.dap/memory.exp

diff --git a/gdb/testsuite/gdb.dap/memory.exp b/gdb/testsuite/gdb.dap/memory.exp
index ab0516d..d702d5b 100644
--- a/gdb/testsuite/gdb.dap/memory.exp
+++ b/gdb/testsuite/gdb.dap/memory.exp
@@ -47,6 +47,8 @@
 	     evaluate {o expression [s thirty_two]}]
 dap_match_values "global value" [lindex $obj 0] "body result" 7
 
+set obj [dap_check_request_and_response "evaluate global pointer" \
+	     evaluate {o expression [s thirty_two_p]}]
 set addr [dict get [lindex $obj 0] body memoryReference]
 
 set obj [dap_check_request_and_response "read memory" \

gdb/testsuite/lib/dap-support.exp

diff --git a/gdb/testsuite/lib/dap-support.exp b/gdb/testsuite/lib/dap-support.exp
index 657ad7b..2a0cb88 100644
--- a/gdb/testsuite/lib/dap-support.exp
+++ b/gdb/testsuite/lib/dap-support.exp
@@ -233,7 +233,8 @@
     return [dap_check_request_and_response $name initialize \
 		{o clientID [s "gdb testsuite"] \
 		     supportsVariableType [l true] \
-		     supportsVariablePaging [l true]}]
+		     supportsVariablePaging [l true] \
+		     supportsMemoryReferences [l true]}]
 }
 
 # Start gdb, send a DAP initialize request, and then a launch request