Introduce sourceReference handling in DAP

This changes the gdb DAP implementation to emit a real
sourceReference, rather than emitting 0.  Sources are tracked in some
maps in sources.py, and a new helper function is introduced to compute
the "Source" object that can be sent to the client.

gdb/python/lib/gdb/dap/breakpoint.py

@@ -23,6 +23,7 @@ from contextlib import contextmanager
 from typing import Optional, Sequence
 
 from .server import request, capability, send_event
+from .sources import make_source
 from .startup import send_gdb_with_response, in_gdb_thread, log_stack
 from .typecheck import type_check
 
@@ -105,15 +106,10 @@ def _breakpoint_descriptor(bp):
         # multiple locations.  See
         # https://github.com/microsoft/debug-adapter-protocol/issues/13
         loc = bp.locations[0]
-        (basename, line) = loc.source
+        (filename, line) = loc.source
         result.update(
             {
-                "source": {
-                    "name": os.path.basename(basename),
-                    # We probably don't need this but it doesn't hurt to
-                    # be explicit.
-                    "sourceReference": 0,
-                },
+                "source": make_source(filename, os.path.basename(filename)),
                 "line": line,
                 "instructionReference": hex(loc.address),
             }

gdb/python/lib/gdb/dap/bt.py

@@ -20,6 +20,7 @@ from gdb.frames import frame_iterator
 from .frames import frame_id
 from .modules import module_id
 from .server import request, capability
+from .sources import make_source
 from .startup import send_gdb_with_response, in_gdb_thread
 from .state import set_thread
 from .varref import apply_format
@@ -61,13 +62,7 @@ def _backtrace(thread_id, levels, startFrame, value_format):
                 newframe["line"] = line
             filename = current_frame.filename()
             if filename is not None:
-                newframe["source"] = {
-                    "name": os.path.basename(filename),
-                    "path": filename,
-                    # We probably don't need this but it doesn't hurt
-                    # to be explicit.
-                    "sourceReference": 0,
-                }
+                newframe["source"] = make_source(filename, os.path.basename(filename))
             frames.append(newframe)
         # Note that we do not calculate totalFrames here.  Its absence
         # tells the client that it may simply ask for frames until a

gdb/python/lib/gdb/dap/sources.py

@@ -19,16 +19,46 @@ from .server import request, capability
 from .startup import send_gdb_with_response, in_gdb_thread
 
 
+# The next available source reference ID.  Must be greater than 0.
+_next_source = 1
+
+# Map from full paths to Source dictionaries.
+_source_map = {}
+
+# Map from a source reference ID back to the same Source that is
+# stored in _source_map.
+_id_map = {}
+
+
+@in_gdb_thread
+def make_source(fullname, filename):
+    """Return the Source for a given file name.
+
+    FULLNAME is the full name.  This is used as the key.
+    FILENAME is the base name.
+    """
+    global _source_map
+    if fullname in _source_map:
+        result = _source_map[fullname]
+    else:
+        global _next_source
+        result = {
+            "name": filename,
+            "path": fullname,
+            "sourceReference": _next_source,
+        }
+        _source_map[fullname] = result
+        global _id_map
+        _id_map[_next_source] = result
+        _next_source += 1
+    return result
+
+
 @in_gdb_thread
 def _sources():
     result = []
     for elt in gdb.execute_mi("-file-list-exec-source-files")["files"]:
-        result.append(
-            {
-                "name": elt["file"],
-                "path": elt["fullname"],
-            }
-        )
+        result.append(make_source(elt["fullname"], elt["file"]))
     return {
         "sources": result,
     }