Make 'pylint' equivalent to 'pylint .'

Closes #5701

Author: Pierre-Sassoulas

Diff for: doc/whatsnew/fragments/5701.breaking

@@ -0,0 +1,4 @@
+``pylint`` is now equivalent to ``pylint .`` and won't show the help by default anymore.
+The help is still available with ``pylint --help`` or ``pylint --long-help``.
+
+Closes #5701

Diff for: pylint/lint/pylinter.py

@@ -658,13 +658,14 @@ def check(self, files_or_modules: Sequence[str]) -> None:
         files_or_modules is either a string or list of strings presenting modules to check.
         """
         self.initialize()
+        if not files_or_modules and not self.config.from_stdin:
+            files_or_modules = (str(Path(".").resolve()),)
         if self.config.recursive:
             files_or_modules = tuple(self._discover_files(files_or_modules))
         if self.config.from_stdin:
             if len(files_or_modules) != 1:
-                raise exceptions.InvalidArgsError(
-                    "Missing filename required for --from-stdin"
-                )
+                print("Missing filename required for --from-stdin")
+                sys.exit(32)
 
         extra_packages_paths = list(
             {
@@ -989,7 +990,14 @@ def get_ast(
                 confidence=HIGH,
             )
         except astroid.AstroidBuildingError as ex:
-            self.add_message("parse-error", args=ex)
+            msg = str(ex)
+            if "Unable to load file" in msg and "__init__.py" in msg:
+                msg = (
+                    "No '__init__.py' in the given directory, give a python module, "
+                    "or use '--recursive=y' with the proper ignore option (in order"
+                    " to not lint your virtualenv)"
+                )
+            self.add_message("parse-error", args=msg)
         except Exception as ex:
             traceback.print_exc()
             # We raise BuildingError here as this is essentially an astroid issue

Diff for: pylint/lint/run.py

@@ -176,10 +176,8 @@ def __init__(
             return
 
         # Display help if there are no files to lint or no checks enabled
-        if not args or len(linter.config.disable) == len(
-            linter.msgs_store._messages_definitions
-        ):
-            print("No files to lint: exiting.")
+        if len(linter.config.disable) == len(linter.msgs_store._messages_definitions):
+            print("No messages to check: exiting.")
             sys.exit(32)
 
         if linter.config.jobs < 0:

Diff for: tests/test_self.py

@@ -211,12 +211,12 @@ def test_nonexistent_config_file(self) -> None:
         self._runtest(["--rcfile=/tmp/this_file_does_not_exist"], code=32)
 
     def test_error_missing_arguments(self) -> None:
-        self._runtest([], code=32)
+        self._runtest([], code=1)
 
     def test_disable_all(self) -> None:
         out = StringIO()
         self._runtest([UNNECESSARY_LAMBDA, "--disable=all"], out=out, code=32)
-        assert "No files to lint: exiting." in out.getvalue().strip()
+        assert "No messages to check: exiting." in out.getvalue().strip()
 
     def test_no_out_encoding(self) -> None:
         """Test redirection of stdout with non ascii characters."""
@@ -491,8 +491,9 @@ def test_pylintrc_comments_in_values(self) -> None:
         )
 
     def test_no_crash_with_formatting_regex_defaults(self) -> None:
+        path = join(HERE, "regrtest_data", "empty.py")
         self._runtest(
-            ["--ignore-patterns=a"], reporter=TextReporter(StringIO()), code=32
+            [path, "--ignore-patterns=a"], reporter=TextReporter(StringIO()), code=0
         )
 
     def test_getdefaultencoding_crashes_with_lc_ctype_utf8(self) -> None: