introduce warning system with this API:

- node.warn() for a node-specific warning
- config.warn() for a global non-node specific warning

Each warning is accompanied by a "warning number" so that we can later
introduce mechanisms for surpressing them.

Each warning will trigger a call to pytest_report_warn(number, node, message)
which is by default implemented by the TerminalReporter which introduces
a new option "-rw" to show details about warnings.

_pytest/config.py

@@ -613,6 +613,11 @@ class Config(object):
         self.hook.pytest_unconfigure(config=self)
         self.pluginmanager.ensure_shutdown()
 
+    def warn(self, code, message):
+        """ generate a warning for this test session. """
+        self.hook.pytest_logwarning(code=code, message=message,
+                                    fslocation=None, nodeid=None)
+
     def pytest_cmdline_parse(self, pluginmanager, args):
         assert self == pluginmanager.config, (self, pluginmanager.config)
         self.parse(args)

_pytest/hookspec.py

@@ -227,6 +227,11 @@ pytest_report_teststatus.firstresult = True
 def pytest_terminal_summary(terminalreporter):
     """ add additional section in terminal summary reporting.  """
 
+def pytest_logwarning(message, code, nodeid, fslocation):
+    """ process a warning specified by a message, a code string,
+    a nodeid and fslocation (both of which may be None
+    if the warning is not tied to a partilar node/location)."""
+
 # -------------------------------------------------------------------------
 # doctest hooks
 # -------------------------------------------------------------------------

_pytest/main.py

@@ -263,6 +263,20 @@ class Node(object):
         return "<%s %r>" %(self.__class__.__name__,
                            getattr(self, 'name', None))
 
+    def warn(self, code, message):
+        """ generate a warning with the given code and message for this
+        item. """
+        assert isinstance(code, str)
+        fslocation = getattr(self, "location", None)
+        if fslocation is None:
+            fslocation = getattr(self, "fspath", None)
+        else:
+            fslocation = "%s:%s" % fslocation[:2]
+
+        self.ihook.pytest_logwarning(code=code, message=message,
+                                     nodeid=self.nodeid,
+                                     fslocation=fslocation)
+
     # methods for ordering nodes
     @property
     def nodeid(self):

_pytest/terminal.py

@@ -75,6 +75,14 @@ def pytest_report_teststatus(report):
             letter = "f"
     return report.outcome, letter, report.outcome.upper()
 
+class WarningReport:
+    def __init__(self, code, message, nodeid=None, fslocation=None):
+        self.code = code
+        self.message = message
+        self.nodeid = nodeid
+        self.fslocation = fslocation
+
+
 class TerminalReporter:
     def __init__(self, config, file=None):
         self.config = config
@@ -151,6 +159,12 @@ class TerminalReporter:
             self.write_line("INTERNALERROR> " + line)
         return 1
 
+    def pytest_logwarning(self, code, fslocation, message, nodeid):
+        warnings = self.stats.setdefault("warnings", [])
+        warning = WarningReport(code=code, fslocation=fslocation,
+                                message=message, nodeid=nodeid)
+        warnings.append(warning)
+
     def pytest_plugin_registered(self, plugin):
         if self.config.option.traceconfig:
             msg = "PLUGIN registered: %s" % (plugin,)
@@ -335,6 +349,7 @@ class TerminalReporter:
             self.summary_errors()
             self.summary_failures()
             self.summary_hints()
+            self.summary_warnings()
             self.config.hook.pytest_terminal_summary(terminalreporter=self)
         if exitstatus == 2:
             self._report_keyboardinterrupt()
@@ -405,6 +420,16 @@ class TerminalReporter:
             for hint in self.config.pluginmanager._hints:
                 self._tw.line("hint: %s" % hint)
 
+    def summary_warnings(self):
+        if self.hasopt("w"):
+            warnings = self.stats.get("warnings")
+            if not warnings:
+                return
+            self.write_sep("=", "warning summary")
+            for w in warnings:
+                self._tw.line("W%s %s %s" % (w.code,
+                              w.fslocation, w.message))
+
     def summary_failures(self):
         if self.config.option.tbstyle != "no":
             reports = self.getreports('failed')
@@ -449,7 +474,8 @@ class TerminalReporter:
     def summary_stats(self):
         session_duration = py.std.time.time() - self._sessionstarttime
 
-        keys = "failed passed skipped deselected xfailed xpassed".split()
+        keys = ("failed passed skipped deselected "
+               "xfailed xpassed warnings").split()
         for key in self.stats.keys():
             if key not in keys:
                 keys.append(key)

testing/test_config.py

@@ -360,4 +360,43 @@ def test_load_initial_conftest_last_ordering(testdir):
     assert l[-2] == m.pytest_load_initial_conftests
     assert l[-3].__module__ == "_pytest.config"
 
+class TestWarning:
+    def test_warn_config(self, testdir):
+        testdir.makeconftest("""
+            l = []
+            def pytest_configure(config):
+                config.warn("C1", "hello")
+            def pytest_logwarning(code, message):
+                assert code == "C1"
+                assert message == "hello"
+                l.append(1)
+        """)
+        testdir.makepyfile("""
+            def test_proper(pytestconfig):
+                import conftest
+                assert conftest.l == [1]
+        """)
+        reprec = testdir.inline_run()
+        reprec.assertoutcome(passed=1)
 
+    def test_warn_on_test_item_from_request(self, testdir):
+        testdir.makepyfile("""
+            import pytest
+
+            @pytest.fixture
+            def fix(request):
+                request.node.warn("T1", "hello")
+            def test_hello(fix):
+                pass
+        """)
+        result = testdir.runpytest()
+        result.stdout.fnmatch_lines("""
+            *1 warning*
+        """)
+        assert "hello" not in result.stdout.str()
+        result = testdir.runpytest("-rw")
+        result.stdout.fnmatch_lines("""
+            ===*warning summary*===
+            *WT1*test_warn_on_test_item*:5*hello*
+            *1 warning*
+        """)