Warn when duplicate cores are encountered

The rules for how several cores with the same VLNV are handled is
clearly defined. It is however very easy to miss if users have made
a mistake. FuseSoC printed a debug message about this, but it is
likely more user-friendly to print this as a warning instead.

fusesoc/coremanager.py

@@ -71,7 +71,7 @@ def add(self, core, library):
         logger.debug("Adding core " + name)
         if name in self._cores:
             _s = "Replacing {} in {} with the version found in {}"
-            logger.debug(
+            logger.warning(
                 _s.format(name, self._cores[name]["core"].core_root, core.core_root)
             )
         self._cores[name] = {"core": core, "library": library}

tests/capi2_cores/override/1/basic.core

@@ -0,0 +1,9 @@
+CAPI=2:
+# Copyright FuseSoC contributors
+# Licensed under the 2-Clause BSD License, see LICENSE for details.
+# SPDX-License-Identifier: BSD-2-Clause
+
+name: ::basic:0
+
+targets:
+  default: {}

tests/capi2_cores/override/2/basic.core

@@ -0,0 +1,9 @@
+CAPI=2:
+# Copyright FuseSoC contributors
+# Licensed under the 2-Clause BSD License, see LICENSE for details.
+# SPDX-License-Identifier: BSD-2-Clause
+
+name: ::basic:0
+
+targets:
+  default: {}

tests/test_coremanager.py

@@ -213,6 +213,26 @@ def test_export():
     ]:
         assert os.path.isfile(os.path.join(export_root, f))
 
+def test_override(caplog):
+    import logging
+    import os
+    from fusesoc.config import Config
+    from fusesoc.coremanager import CoreManager
+    from fusesoc.librarymanager import Library
+    from fusesoc.vlnv import Vlnv
+
+    core_base_dir = os.path.join(os.path.dirname(__file__), "capi2_cores", "override")
+    cm = CoreManager(Config())
+    with caplog.at_level(logging.WARNING):
+        cm.add_library(Library("1", os.path.join(core_base_dir,"1")), [])
+    assert caplog.text == ""
+
+    with caplog.at_level(logging.WARNING):
+        cm.add_library(Library("2", os.path.join(core_base_dir,"2")), [])
+    assert "Replacing ::basic:0 in" in caplog.text
+
+    core = cm.get_core(Vlnv("::basic"))
+    assert core.core_root.endswith("2")
 
 def test_virtual():
     import os