mark: deprecate a couple undocumented -k syntaxes

The `-k '-expr'` syntax is an old alias to `-k 'not expr'`. It's also
not a very convenient to have syntax that start with `-` on the CLI.
Deprecate it and suggest replacing with `not`.

---

The `-k 'expr:'` syntax discards all items until the first match and
keeps all subsequent, e.g. `-k foo` with

    test_bar
    test_foo
    test_baz

results in `test_foo`, `test_baz`. That's a bit weird, so deprecate it
without a replacement. If someone complains we can reconsider or devise
a better alternative.

1 files changed, 10 insertions, 0 deletions

diff --git a/src/_pytest/deprecated.py b/src/_pytest/deprecated.py
index 8c9bd9d5c..9f4570f85 100644
--- a/src/_pytest/deprecated.py
+++ b/src/_pytest/deprecated.py
@@ -75,3 +75,13 @@ TERMINALWRITER_WRITER = PytestDeprecationWarning(
     "The TerminalReporter.writer attribute is deprecated, use TerminalReporter._tw instead at your own risk.\n"
     "See https://docs.pytest.org/en/latest/deprecations.html#terminalreporter-writer for more information."
 )
+
+
+MINUS_K_DASH = PytestDeprecationWarning(
+    "The `-k '-expr'` syntax to -k is deprecated.\nUse `-k 'not expr'` instead."
+)
+
+MINUS_K_COLON = PytestDeprecationWarning(
+    "The `-k 'expr:'` syntax to -k is deprecated.\n"
+    "Please open an issue if you use this and want a replacement."
+)