[PATCH RFC 3/6] Allow missing build-id when finding an objfile

[Tom Tromey <tromey@adacore.com>]

Currently the "missing objfile" code requires a build-id.

However, in my situation, the build-id is not known.  But, aside from
this small detail, the missing objfile code looked close to what I
wanted to implement.

This patch extends the API to allow the build-id to be missing.  In
this case, None is passed to Python.

However, because this is an API change, MissingObjfileHandler is also
extended to record whether the build-id is required.  And, by default
it is required, so that existing handlers won't be called in this new
situation.
---
 gdb/python/lib/gdb/__init__.py        | 17 +++++++++++++----
 gdb/python/lib/gdb/missing_objfile.py |  4 ++++
 gdb/python/python.c                   | 17 +++++++++++------
 3 files changed, 28 insertions(+), 10 deletions(-)

diff --git a/gdb/python/lib/gdb/__init__.py b/gdb/python/lib/gdb/__init__.py
index 1a4aefcd802..f16e0a66c5b 100644
--- a/gdb/python/lib/gdb/__init__.py
+++ b/gdb/python/lib/gdb/__init__.py
@@ -382,7 +382,8 @@ def _handle_missing_objfile(pspace, buildid, filename):
         pspace: A gdb.Progspace for which the missing objfile handlers
                 should be run.  This is the program space in which an
                 objfile was found to be missing.
-        buildid: A string containing the build-id we're looking for.
+        buildid: A string containing the build-id we're looking for,
+                 or None if the buildid is not known.
         filename: The filename of the file GDB tried to find but
                   couldn't.  This is not where the file should be
                   placed if found, in fact, this file might already
@@ -403,9 +404,17 @@ def _handle_missing_objfile(pspace, buildid, filename):
                   missing objfile.
     """
 
-    return _handle_missing_files(
-        pspace, "objfile", lambda h: h(pspace, buildid, filename)
-    )
+    # Delay this as long as possible.
+    from gdb.missing_objfile import MissingObjfileHandler
+
+    def maybe_call_handler(handler):
+        if buildid is not None or (
+            isinstance(handler, MissingObjfileHandler) and not handler.buildid_required
+        ):
+            return handler(pspace, buildid, filename)
+        return None
+
+    return _handle_missing_files(pspace, "objfile", maybe_call_handler)
 
 
 class ParameterPrefix:
diff --git a/gdb/python/lib/gdb/missing_objfile.py b/gdb/python/lib/gdb/missing_objfile.py
index 45661d0f415..fe45a418c6d 100644
--- a/gdb/python/lib/gdb/missing_objfile.py
+++ b/gdb/python/lib/gdb/missing_objfile.py
@@ -30,8 +30,12 @@ class MissingObjfileHandler(MissingFileHandler):
     Attributes:
         name: Read-only attribute, the name of this handler.
         enabled: When true this handler is enabled.
+        buildid_required: When False, this handler can accept a
+              request with buildid=None.
     """
 
+    buildid_required = True
+
     def __call__(self, buildid, filename):
         """Handle a missing objfile when GDB can knows the build-id.
 
diff --git a/gdb/python/python.c b/gdb/python/python.c
index 5a9c876c197..06ad0876527 100644
--- a/gdb/python/python.c
+++ b/gdb/python/python.c
@@ -1950,7 +1950,6 @@ gdbpy_find_objfile_from_buildid (const struct extension_language_defn *extlang,
 				 const char *missing_filename)
 {
   gdb_assert (pspace != nullptr);
-  gdb_assert (build_id != nullptr);
   gdb_assert (missing_filename != nullptr);
 
   /* Early exit if Python is not initialised.  */
@@ -1960,12 +1959,18 @@ gdbpy_find_objfile_from_buildid (const struct extension_language_defn *extlang,
   gdbpy_enter enter_py;
 
   /* Convert BUILD_ID into a Python object.  */
-  std::string hex_form = bin2hex (build_id->data, build_id->size);
-  gdbpy_ref<> pyo_buildid = host_string_to_python_string (hex_form.c_str ());
-  if (pyo_buildid == nullptr)
+  gdbpy_ref<> pyo_buildid;
+  if (build_id == nullptr)
+    pyo_buildid = gdbpy_ref<>::new_reference (Py_None);
+  else
     {
-      gdbpy_print_stack ();
-      return {};
+      std::string hex_form = bin2hex (build_id->data, build_id->size);
+      pyo_buildid = host_string_to_python_string (hex_form.c_str ());
+      if (pyo_buildid == nullptr)
+	{
+	  gdbpy_print_stack ();
+	  return {};
+	}
     }
 
   /* Convert MISSING_FILENAME to a Python object.  */

-- 
2.56.0