Test handling of realistic out-of-tree builds

The JSON compilation databases used in this test are designed to mimic those
generated by CMake. Notably, the "file" field of such databases is an absolute
path to a file in the source directory.

Signed-off-by: John Pennycook <john.pennycook@intel.com>

Author: Pennycook

tests/build-dir/__init__.py

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+# Copyright (C) 2021 Intel Corporation
+# SPDX-License-Identifier: BSD-3-Clause

tests/build-dir/foo.cpp

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+void foo() { return; }

tests/build-dir/test_build_dir.py

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+# Copyright (C) 2024 Intel Corporation
+# SPDX-License-Identifier: BSD-3-Clause
+
+import json
+import logging
+import tempfile
+import unittest
+from pathlib import Path
+
+from codebasin import config, finder
+from codebasin.walkers.platform_mapper import PlatformMapper
+
+
+class TestBuildDirectories(unittest.TestCase):
+    """
+    Test ability to correctly handle out-of-tree builds.
+    """
+
+    def setUp(self):
+        self.rootdir = str(Path(__file__).parent)
+        logging.getLogger("codebasin").disabled = True
+
+    def test_absolute_paths(self):
+        """
+        Test database with build "directory" path but source "file" path.
+        All "file" fields are absolute paths.
+        """
+
+        source = str(Path(__file__).parent.joinpath("foo.cpp"))
+
+        # CBI only understands how to load compilation databases from file.
+        # For now, create temporary files every time we test.
+        dir1 = str(Path(__file__).parent.joinpath("build1/"))
+        build1 = tempfile.NamedTemporaryFile()
+        json1 = [
+            {
+                "command": f"/usr/bin/c++ -o foo.cpp.o -c {source}",
+                "directory": f"{dir1}",
+                "file": f"{source}",
+            },
+        ]
+        with open(build1.name, "w") as f:
+            json.dump(json1, f)
+
+        dir2 = str(Path(__file__).parent.joinpath("build2/"))
+        build2 = tempfile.NamedTemporaryFile()
+        json2 = [
+            {
+                "command": f"/usr/bin/c++ -o foo.cpp.o -c {source}",
+                "directory": f"{dir2}",
+                "file": f"{source}",
+            },
+        ]
+        with open(build2.name, "w") as f:
+            json.dump(json2, f)
+
+        codebase = {
+            "files": [source],
+            "platforms": ["one", "two"],
+            "exclude_files": set(),
+            "exclude_patterns": [],
+            "rootdir": self.rootdir,
+        }
+
+        configuration = {}
+        for name, path in [("one", build1.name), ("two", build2.name)]:
+            db = config.load_database(path, self.rootdir)
+            configuration.update({name: db})
+
+        expected_setmap = {frozenset(["one", "two"]): 1}
+
+        state = finder.find(self.rootdir, codebase, configuration)
+        mapper = PlatformMapper(codebase)
+        setmap = mapper.walk(state)
+        self.assertDictEqual(setmap, expected_setmap, "Mismatch in setmap")
+
+
+if __name__ == "__main__":
+    unittest.main()