gdbsupport/selftest: Allow lazy registration

This patch adds a way to delay the registration of tests until the
latest possible moment.  This is intended for situations where GDB needs
to be fully initialized in order to decide if a particular selftest can
be executed or not.

This mechanism will be used in the next patch.

Change-Id: I7f6b061f4c0a6832226c7080ab4e3a2523e1b0b0

gdbsupport/selftest.cc

diff --git a/gdbsupport/selftest.cc b/gdbsupport/selftest.cc
index 7077f11..1b862bb 100644
--- a/gdbsupport/selftest.cc
+++ b/gdbsupport/selftest.cc
@@ -30,6 +30,11 @@
 
 static selftests_registry tests;
 
+/* Set of callback functions used to register selftests after GDB is fully
+   initialized.  */
+
+static std::vector<selftests_generator> lazy_generators;
+
 /* See selftest.h.  */
 
 void
@@ -44,6 +49,14 @@
 
 /* See selftest.h.  */
 
+void
+add_lazy_generator (selftests_generator generator)
+{
+  lazy_generators.push_back (std::move (generator));
+}
+
+/* See selftest.h.  */
+
 static bool run_verbose_ = false;
 
 /* See selftest.h.  */
@@ -104,6 +117,14 @@
 selftests_range
 all_selftests ()
 {
+  /* Execute any function which might still want to register tests.  Once each
+     function has been executed, clear lazy_generators to ensure that
+     callback functions are only executed once.  */
+  for (const auto &generator : lazy_generators)
+    for (selftest &test : generator ())
+      register_test (std::move (test.name), std::move (test.test));
+  lazy_generators.clear ();
+
   return selftests_range (tests.cbegin (), tests.cend ());
 }
 

gdbsupport/selftest.h

diff --git a/gdbsupport/selftest.h b/gdbsupport/selftest.h
index 5ca9bdc..661431d 100644
--- a/gdbsupport/selftest.h
+++ b/gdbsupport/selftest.h
@@ -23,6 +23,7 @@
 #include "gdbsupport/function-view.h"
 #include "gdbsupport/iterator-range.h"
 #include <set>
+#include <vector>
 
 /* A test is just a function that does some checks and throws an
    exception if something has gone wrong.  */
@@ -61,6 +62,16 @@ extern bool run_verbose ();
 extern void register_test (const std::string &name,
 			   std::function<void(void)> function);
 
+/* A selftest generator is a callback function used to delay the generation
+   of selftests.  */
+
+using selftests_generator = std::function<std::vector<selftest> (void)>;
+
+/* Register a function which can lazily register selftests once GDB is fully
+   initialized. */
+
+extern void add_lazy_generator (selftests_generator generator);
+
 /* Run all the self tests.  This print a message describing the number
    of test and the number of failures.