Warnings can be marked to only display once.

3 files changed, 28 insertions, 6 deletions

diff --git a/coverage/control.py b/coverage/control.py
index 6e59078c..4358a541 100644
--- a/coverage/control.py
+++ b/coverage/control.py
@@ -203,6 +203,7 @@ class Coverage(object):
         self._warn_no_data = True
         self._warn_unimported_source = True
         self._warn_preimported_source = check_preimported
+        self._no_warn_slugs = None
 
         # A record of all the warnings that have been issued.
         self._warnings = []
@@ -333,12 +334,19 @@ class Coverage(object):
 
         return not reason
 
-    def _warn(self, msg, slug=None):
+    def _warn(self, msg, slug=None, once=False):
         """Use `msg` as a warning.
 
         For warning suppression, use `slug` as the shorthand.
+
+        If `once` is true, only show this warning once (determined by the
+        slug.)
+
         """
-        if slug in self.config.disable_warnings:
+        if self._no_warn_slugs is None:
+            self._no_warn_slugs = list(self.config.disable_warnings)
+
+        if slug in self._no_warn_slugs:
             # Don't issue the warning
             return
 
@@ -349,6 +357,9 @@ class Coverage(object):
             msg = "[%d] %s" % (os.getpid(), msg)
         sys.stderr.write("Coverage.py warning: %s\n" % msg)
 
+        if once:
+            self._no_warn_slugs.append(slug)
+
     def get_option(self, option_name):
         """Get an option from the configuration.
 
diff --git a/tests/coveragetest.py b/tests/coveragetest.py
index 17b3f15d..1917c5b3 100644
--- a/tests/coveragetest.py
+++ b/tests/coveragetest.py
@@ -264,8 +264,9 @@ class CoverageTest(
 
         """
         saved_warnings = []
-        def capture_warning(msg, slug=None):
+        def capture_warning(msg, slug=None, once=False):        # pylint: disable=unused-argument
             """A fake implementation of Coverage._warn, to capture warnings."""
+            # NOTE: we don't implement `once`.
             if slug:
                 msg = "%s (%s)" % (msg, slug)
             saved_warnings.append(msg)
diff --git a/tests/test_api.py b/tests/test_api.py
index 369324f7..63a0c7b1 100644
--- a/tests/test_api.py
+++ b/tests/test_api.py
@@ -532,12 +532,22 @@ class ApiTest(CoverageTest):
         self.assertIn("Hello\n", out)
 
         err = self.stderr()
-        self.assertIn(textwrap.dedent("""\
-            Coverage.py warning: Module sys has no Python source. (module-not-python)
-            """), err)
+        self.assertIn(
+            "Coverage.py warning: Module sys has no Python source. (module-not-python)",
+            err
+        )
         self.assertNotIn("module-not-imported", err)
         self.assertNotIn("no-data-collected", err)
 
+    def test_warn_once(self):
+        cov = coverage.Coverage()
+        cov.load()
+        cov._warn("Warning, warning 1!", slug="bot", once=True)
+        cov._warn("Warning, warning 2!", slug="bot", once=True)
+        err = self.stderr()
+        self.assertIn("Warning, warning 1!", err)
+        self.assertNotIn("Warning, warning 2!", err)
+
     def test_source_and_include_dont_conflict(self):
         # A bad fix made this case fail: https://bitbucket.org/ned/coveragepy/issues/541
         self.make_file("a.py", "import b\na = 1")