venv: Do not fail for test commands that don't exist with "-" leader

CONTRIBUTORS

@@ -24,6 +24,7 @@ Brett Smith
 Bruno Oliveira
 Carl Meyer
 Charles Brunet
+Chris Down
 Chris Jerdonek
 Chris Rose
 Clark Boylan

docs/changelog/2315.feature.rst

@@ -0,0 +1,2 @@
+Ignore missing commands if they are prefixed by ``-``
+-- by :user:`cdown`.

docs/config.rst

@@ -264,7 +264,7 @@ Complete list of settings that you can put into ``testenv*`` sections:
 
     Commands will execute one by one in sequential fashion until one of them fails (their exit
     code is non-zero) or all of them succeed. The exit code of a command may be ignored (meaning
-    they are always considered successful) by prefixing the command with a dash (``-``) - this is
+    they are always considered successful even if they don't exist) by prefixing the command with a dash (``-``) - this is
     similar to how ``make`` recipe lines work. The outcome of the environment is considered successful
     only if all commands (these + setup + teardown) succeeded (exit code ignored via the
     ``-`` or success exit code value of zero).

src/tox/venv.py

@@ -595,7 +595,17 @@ def _pcall(
         reporter.verbosity2("setting PATH={}".format(env["PATH"]))
 
         # get command
-        args[0] = self.getcommandpath(args[0], venv, cwd)
+        try:
+            args[0] = self.getcommandpath(args[0], venv, cwd)
+        except tox.exception.InvocationError:
+            if ignore_ret:
+                self.status = getattr(self, "status", 0)
+                msg = "command not found but explicitly ignored"
+                reporter.warning("{}\ncmd: {}".format(msg, args[0]))
+                return ""  # in case it's returnout
+            else:
+                raise
+
         if sys.platform != "win32" and "TOX_LIMITED_SHEBANG" in os.environ:
             args = prepend_shebang_interpreter(args)
 

tests/unit/test_venv.py

@@ -980,6 +980,21 @@ def test_ignore_outcome_failing_cmd(newmocksession):
     mocksession.report.expect("warning", "*command failed but result from testenv is ignored*")
 
 
+def test_ignore_outcome_missing_cmd(newmocksession):
+    mocksession = newmocksession(
+        [],
+        """\
+        [testenv]
+        commands=-thiscommanddoesntexist
+        """,
+    )
+
+    venv = mocksession.getvenv("python")
+    venv.test()
+    assert venv.status == 0
+    mocksession.report.expect("warning", "*command not found but explicitly ignored*")
+
+
 def test_tox_testenv_create(newmocksession):
     log = []