feat: add config to check files that should be present

Closes #74

README.md

@@ -83,6 +83,7 @@ If a key is defined in more than one file, the value from the last file will pre
 ### Style file syntax
 
 NOTE: The project is still experimental; the style file syntax might slightly change before the 1.0 stable release.
+The `NIP*` error codes also might change.
 
 A style file contains basically the configuration options you want to enforce in all your projects.
 
@@ -111,6 +112,15 @@ To enforce all your projects to ignore missing imports, add this to your `nitpic
     ["setup.cfg".mypy]
     ignore_missing_imports = true
 
+### Present files
+
+To enforce that certain files should exist in the project, you can add them to the style file as a dictionary of "file name" and "extra message".
+Use an empty string to not display any extra message.
+
+    [nitpick.files.present]
+    ".editorconfig" = ""
+    "CHANGELOG.md" = "A project should have a changelog"
+
 ### Absent files
 
 To enforce that certain files should not exist in the project, you can add them to the style file.

src/nitpick/files/base.py

@@ -72,6 +72,7 @@ def check_exists(self) -> YieldFlake8Error:
             if config_data_exists and not file_exists:
                 suggestion = self.suggest_initial_contents()
                 phrases = [" was not found"]
+                # TODO: add validation for missing_message on the BaseFileSchema
                 missing_message = self.nitpick_file_dict.get("missing_message", "")
                 if missing_message:
                     phrases.append(missing_message)

src/nitpick/plugin.py

@@ -51,23 +51,28 @@ def run(self) -> YieldFlake8Error:
             return []
         LOGGER.info("Nitpicking file: %s", self.filename)
 
-        yield from itertools.chain(self.config.merge_styles(), self.check_absent_files())
+        yield from itertools.chain(self.config.merge_styles(), self.check_files(True), self.check_files(False))
 
         for checker_class in get_subclasses(BaseFile):
             checker = checker_class()
             yield from checker.check_exists()
 
         return []
 
-    def check_absent_files(self) -> YieldFlake8Error:
-        """Check absent files."""
-        for file_name, delete_message in self.config.files.get("absent", {}).items():
+    def check_files(self, present: bool) -> YieldFlake8Error:
+        """Check files that should be present or absent."""
+        # TODO: validate with schemas
+        key = "present" if present else "absent"
+        message = "exist" if present else "be deleted"
+        absent = not present
+        for file_name, extra_message in self.config.files.get(key, {}).items():
             file_path = self.config.root_dir / file_name  # type: Path
-            if not file_path.exists():
+            exists = file_path.exists()
+            if (present and exists) or (absent and not exists):
                 continue
 
-            full_message = "File {} should be deleted".format(file_name)
-            if delete_message:
-                full_message += ": {}".format(delete_message)
+            full_message = "File {} should {}".format(file_name, message)
+            if extra_message:
+                full_message += ": {}".format(extra_message)
 
-            yield self.flake8_error(3, full_message)
+            yield self.flake8_error(3 if present else 4, full_message)

tests/test_plugin.py

@@ -11,7 +11,36 @@ def test_absent_files(request):
         yyy = "Remove that"
         """
     ).touch_file("xxx").touch_file("yyy").lint().assert_errors_contain(
-        "NIP103 File xxx should be deleted: Remove this"
+        "NIP104 File xxx should be deleted: Remove this"
     ).assert_errors_contain(
-        "NIP103 File yyy should be deleted: Remove that"
+        "NIP104 File yyy should be deleted: Remove that"
+    )
+
+
+def test_present_files(request):
+    """Test present files from the style configuration."""
+    project = ProjectMock(request)
+    project.style(
+        """
+        [nitpick.files.".editorconfig"]
+        missing_message = "Create this file"
+        """
+    ).lint().assert_errors_contain(
+        """
+        NIP001 File nitpick-style.toml has an incorrect style. Invalid TOML:\x1b[92m
+        TomlDecodeError: Invalid group name \'editorconfig"\'. Try quoting it. (line 1 column 1 char 0)\x1b[0m
+        """
+    )
+
+    project.style(
+        """
+        [nitpick.files.present]
+        ".editorconfig" = "Create this file"
+        ".env" = ""
+        "another-file.txt" = ""
+        """
+    ).lint().assert_errors_contain("NIP103 File .editorconfig should exist: Create this file").assert_errors_contain(
+        "NIP103 File .env should exist"
+    ).assert_errors_contain(
+        "NIP103 File another-file.txt should exist", 3
     )