Have DAP handle non-Value results from 'children'

A pretty-printer's 'children' method may return values other than a
gdb.Value -- it may return any value that can be converted to a
gdb.Value.

I noticed that this case did not work for DAP.  This patch fixes the
problem.

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

@@ -199,9 +199,14 @@ class VariableReference(BaseReference):
         if isinstance(self.printer, gdb.ValuePrinter) and hasattr(
             self.printer, "child"
         ):
-            return self.printer.child(idx)
+            (name, val) = self.printer.child(idx)
         else:
-            return self.cache_children()[idx]
+            (name, val) = self.cache_children()[idx]
+        # A pretty-printer can return something other than a
+        # gdb.Value, but it must be convertible.
+        if not isinstance(val, gdb.Value):
+            val = gdb.Value(val)
+        return (name, val)
 
 
 @in_gdb_thread

gdb/testsuite/gdb.dap/children.exp

@@ -0,0 +1,118 @@
+# Copyright 2023 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Test the handling of non-Value responses from 'children' method.
+
+require allow_dap_tests
+
+load_lib dap-support.exp
+
+standard_testfile lazy-string.c
+
+if {[build_executable ${testfile}.exp $testfile $srcfile] == -1} {
+    return
+}
+
+set remote_python_file [gdb_remote_download host \
+			    ${srcdir}/${subdir}/${testfile}.py]
+
+save_vars GDBFLAGS {
+    append GDBFLAGS " -iex \"source $remote_python_file\""
+
+    if {[dap_launch $testfile] == ""} {
+	return
+    }
+}
+
+set line [gdb_get_line_number "STOP"]
+set obj [dap_check_request_and_response "set breakpoint by line number" \
+	     setBreakpoints \
+	     [format {o source [o path [%s]] breakpoints [a [o line [i %d]]]} \
+		  [list s $srcfile] $line]]
+set line_bpno [dap_get_breakpoint_number $obj]
+
+dap_check_request_and_response "start inferior" configurationDone
+
+dap_wait_for_event_and_check "stopped at line breakpoint" stopped \
+    "body reason" breakpoint \
+    "body hitBreakpointIds" $line_bpno
+
+set bt [lindex [dap_check_request_and_response "backtrace" stackTrace \
+		    {o threadId [i 1]}] \
+	    0]
+set frame_id [dict get [lindex [dict get $bt body stackFrames] 0] id]
+
+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]
+
+lassign $scopes scope reg_scope
+gdb_assert {[dict get $scope name] == "Locals"} "scope is locals"
+gdb_assert {[dict get $scope namedVariables] == 1} "one var in scope"
+
+set num [dict get $scope variablesReference]
+set refs [lindex [dap_check_request_and_response "fetch variable" \
+		      "variables" \
+		      [format {o variablesReference [i %d] count [i 1]} \
+			   $num]] \
+	      0]
+
+set vars [dict get $refs body variables]
+gdb_assert {[llength $vars] == 1} "just one variable"
+
+set var [lindex $vars 0]
+gdb_assert {[dict get $var name] == "the_string"} "variable name"
+gdb_assert {[dict get $var value] == "contents"} "variable value"
+gdb_assert {[dict get $var namedVariables] == 2} "variable has two children"
+
+set num [dict get $var variablesReference]
+set refs [lindex [dap_check_request_and_response "fetch children of variable" \
+		      "variables" \
+		      [format {o variablesReference [i %d] count [i 2]} \
+			   $num]] \
+	      0]
+
+set vars [dict get $refs body variables]
+gdb_assert {[llength $vars] == 2} "got two children of variable"
+
+set saw_first 0
+set saw_second 0
+foreach var [dict get $refs body variables] {
+    set name [dict get $var name]
+    switch $name {
+	"first" {
+	    gdb_assert {[dict get $var value] == 23} "value of first"
+	    incr saw_first
+	}
+
+	"second" {
+	    # The result looks strange here, but only because TON does
+	    # not handle the backslash-quote sequence properly when
+	    # decoding the JSON.  The actual JSON is: "value":
+	    # "\"DEI\"".
+	    gdb_assert {[dict get $var value] == "\\\"DEI\\\""} \
+		"value of second"
+	    incr saw_second
+	}
+
+	default {
+	    fail "unknown variable $name"
+	}
+    }
+}
+
+gdb_assert {$saw_first == 1 && $saw_second == 1} "saw both children"
+
+dap_shutdown

gdb/testsuite/gdb.dap/children.py

@@ -0,0 +1,41 @@
+# Copyright (C) 2023 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+
+import gdb
+
+
+class Printer(gdb.ValuePrinter):
+    """Pretty print test class."""
+
+    def __init__(self, val):
+        self._val = val
+
+    def to_string(self):
+        return "contents"
+
+    def children(self):
+        yield "first", 23
+        yield "second", "DEI"
+
+
+def lookup_function(val):
+    typ = val.type
+    if typ.code == gdb.TYPE_CODE_PTR:
+        return Printer(val)
+    return None
+
+
+gdb.pretty_printers.append(lookup_function)