extract_objects: test and document using the result in a custom_target

QEMU would like to use the result of extract_objects in a custom_target;
examples are using objcopy, or using the object files as the key to look
up command line arguments in compile_commands.json.  This is slightly
peculiar and not covered by the test suite, but it works; in order to avoid
regressions, add a test case and document it.

2 files changed, 27 insertions, 0 deletions

diff --git a/test cases/common/22 object extraction/check-obj.py b/test cases/common/22 object extraction/check-obj.py
new file mode 100644
index 000000000..99c2cc546
--- /dev/null
+++ b/test cases/common/22 object extraction/check-obj.py
@@ -0,0 +1,21 @@
+#! /usr/bin/env python3
+
+import json
+import sys
+import os
+
+cc = None
+output = None
+
+# Only the ninja backend produces compile_commands.json
+if sys.argv[1] == 'ninja':
+    with open('compile_commands.json', 'r') as f:
+        cc = json.load(f)
+    output = set((x['output'] for x in cc))
+
+for obj in sys.argv[2:]:
+    if not os.path.exists(obj):
+        sys.exit(1)
+    if sys.argv[1] == 'ninja' and obj not in output:
+        sys.exit(1)
+    print('Verified', obj)
diff --git a/test cases/common/22 object extraction/meson.build b/test cases/common/22 object extraction/meson.build
index 18be1dbeb..407c5e83b 100644
--- a/test cases/common/22 object extraction/meson.build
+++ b/test cases/common/22 object extraction/meson.build
@@ -16,6 +16,12 @@ else
   e3 = executable('main3', 'main.c', objects : obj3)
   e4 = executable('main4', 'main.c', objects : obj4)
 
+  custom_target('custom_target with object inputs', output: 'objs',
+                input: [obj1, obj2, obj3],
+                build_by_default: true,
+                command: [find_program('check-obj.py'), meson.backend(), '@INPUT@'],
+                capture: true)
+
   test('extraction test 1', e1)
   test('extraction test 2', e2)
   test('extraction test 3', e3)