Deprecate --resultlog cmdline option

Fix pytest-dev#830

_pytest/deprecated.py

@@ -19,3 +19,4 @@
 
 GETFUNCARGVALUE = "use of getfuncargvalue is deprecated, use getfixturevalue"
 
+RESULT_LOG = '--result-log is deprecated and scheduled for removal in pytest 4.0'

_pytest/resultlog.py

@@ -9,7 +9,7 @@ def pytest_addoption(parser):
     group = parser.getgroup("terminal reporting", "resultlog plugin options")
     group.addoption('--resultlog', '--result-log', action="store",
         metavar="path", default=None,
-        help="path for machine-readable result log.")
+        help="DEPRECATED path for machine-readable result log.")
 
 def pytest_configure(config):
     resultlog = config.option.resultlog
@@ -22,6 +22,9 @@ def pytest_configure(config):
         config._resultlog = ResultLog(config, logfile)
         config.pluginmanager.register(config._resultlog)
 
+        from _pytest.deprecated import RESULT_LOG
+        config.warn('C1', RESULT_LOG)
+
 def pytest_unconfigure(config):
     resultlog = getattr(config, '_resultlog', None)
     if resultlog:

doc/en/usage.rst

@@ -251,6 +251,10 @@ This will add a property node below the testsuite node to the generated xml:
 Creating resultlog format files
 ----------------------------------------------------
 
+.. deprecated:: 3.0
+
+    This option is rarely used and is scheduled for removal in 4.0.
+
 To create plain-text machine-readable result files you can issue::
 
     pytest --resultlog=path

testing/deprecated_test.py

@@ -53,3 +53,15 @@ def pytest_logwarning(self, message):
 
 def test_getfuncargvalue_is_deprecated(request):
     pytest.deprecated_call(request.getfuncargvalue, 'tmpdir')
+
+
+def test_resultlog_is_deprecated(testdir):
+    result = testdir.runpytest('--help')
+    result.stdout.fnmatch_lines(['*DEPRECATED path for machine-readable result log*'])
+
+    testdir.makepyfile('''
+        def test():
+            pass
+    ''')
+    result = testdir.runpytest('--result-log=%s' % testdir.tmpdir.join('result.log'))
+    result.stdout.fnmatch_lines(['*--result-log is deprecated and scheduled for removal in pytest 4.0*'])