[PATCH v3 8/8] qapi: switch to use QEMU_TEST_REGENERATE env var

["Daniel P. Berrangé" <berrange@redhat.com>]

The QAPI_TEST_UPDATE env var can be set when running the QAPI
schema tests to regenerate the reference output. For consistent
naming with the tracetool test, change the env var name to
QEMU_TEST_REGENERATE.

The test is modified to provide a hint about use of the new
env var and it is also added to the developer documentation.document its usage.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
---
 docs/devel/testing/main.rst    | 12 ++++++++++++
 tests/qapi-schema/test-qapi.py |  7 +++++--
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/docs/devel/testing/main.rst b/docs/devel/testing/main.rst
index 11f05c0006..fe233fcf7a 100644
--- a/docs/devel/testing/main.rst
+++ b/docs/devel/testing/main.rst
@@ -178,6 +178,18 @@ parser (either fixing a bug or extending/modifying the syntax). To do this:
 
   ``qapi-schema += foo.json``
 
+The reference output can be automatically updated to match the latest QAPI
+code generator by running the tests with the QEMU_TEST_REGENERATE environment
+variable set.
+
+.. code::
+
+   QEMU_TEST_REGENERATE=1 make check-qapi-schema
+
+The resulting changes must be reviewed by the author to ensure they match
+the intended results, before adding the updated reference output to the
+same commit that alters the generator code.
+
 .. _tracetool-tests:
 
 Tracetool tests
diff --git a/tests/qapi-schema/test-qapi.py b/tests/qapi-schema/test-qapi.py
index 4be930228c..cf7fb8a6df 100755
--- a/tests/qapi-schema/test-qapi.py
+++ b/tests/qapi-schema/test-qapi.py
@@ -165,7 +165,7 @@ def test_and_diff(test_name, dir_name, update):
     if actual_out == expected_out and actual_err == expected_err:
         return 0
 
-    print("%s %s" % (test_name, 'UPDATE' if update else 'FAIL'),
+    print("%s: %s" % (test_name, 'UPDATE' if update else 'FAIL'),
           file=sys.stderr)
     out_diff = difflib.unified_diff(expected_out, actual_out, outfp.name)
     err_diff = difflib.unified_diff(expected_err, actual_err, errfp.name)
@@ -173,6 +173,9 @@ def test_and_diff(test_name, dir_name, update):
     sys.stdout.writelines(err_diff)
 
     if not update:
+        print(("\n%s: set QEMU_TEST_REGENERATE=1 to recreate reference output" +
+               "if the QAPI schema generator was intentionally changed") % test_name,
+              file=sys.stderr)
         return 1
 
     try:
@@ -197,7 +200,7 @@ def main(argv):
     parser.add_argument('-d', '--dir', action='store', default='',
                         help="directory containing tests")
     parser.add_argument('-u', '--update', action='store_true',
-                        default='QAPI_TEST_UPDATE' in os.environ,
+                        default='QEMU_TEST_REGENERATE' in os.environ,
                         help="update expected test results")
     parser.add_argument('tests', nargs='*', metavar='TEST', action='store')
     args = parser.parse_args()
-- 
2.50.1