Implement D400 (DocstringEndsInNonPeriod) (#396)

README.md

@@ -217,7 +217,7 @@ ruff also implements some of the most popular Flake8 plugins natively, including
 - [`flake8-print`](https://pypi.org/project/flake8-print/)
 - [`flake8-comprehensions`](https://pypi.org/project/flake8-comprehensions/) (11/16)
 - [`flake8-bugbear`](https://pypi.org/project/flake8-bugbear/) (3/32)
-- [`flake8-docstrings`](https://pypi.org/project/flake8-docstrings/) (1/47)
+- [`flake8-docstrings`](https://pypi.org/project/flake8-docstrings/) (2/47)
 - [`pyupgrade`](https://pypi.org/project/pyupgrade/) (partial)
 
 Beyond rule-set parity, ruff suffers from the following limitations vis-à-vis Flake8:
@@ -304,6 +304,7 @@ The 🛠 emoji indicates that a rule is automatically fixable by the `--fix` com
 | U006 | UsePEP585Annotation | Use `list` instead of `List` for type annotations |  | 🛠 |
 | U007 | UsePEP604Annotation | Use `X \| Y` for type annotations |  | 🛠 |
 | U008 | SuperCallWithParameters | Use `super()` instead of `super(__class__, self)` |  | 🛠 |
+| D400 | DocstringEndsInNonPeriod | First line should end with a period |  |  |
 | D419 | EmptyDocstring | Docstring is empty |  |  |
 | M001 | UnusedNOQA | Unused `noqa` directive |  | 🛠 |
 

resources/test/fixtures/D400.py

@@ -0,0 +1,27 @@
+def f1() -> None:
+    """Hello, world.
+
+    More content here.
+    """
+
+
+def f2() -> None:
+    """Hello, world!
+
+    More content here.
+    """
+
+
+def f3() -> None:
+    """Hello, world
+
+    More content here.
+    """
+
+
+def f4() -> None:
+    """."""
+
+
+def f5() -> None:
+    """"""

src/check_ast.rs

@@ -1890,7 +1890,12 @@ impl<'a> Checker<'a> {
 
     fn check_docstrings(&mut self) {
         while let Some(docstring) = self.docstrings.pop() {
-            docstrings::docstring_empty(self, &docstring);
+            if self.settings.enabled.contains(&CheckCode::D400) {
+                docstrings::ends_with_period(self, &docstring);
+            }
+            if self.settings.enabled.contains(&CheckCode::D419) {
+                docstrings::not_empty(self, &docstring);
+            }
         }
     }
 

src/checks.rs

@@ -151,6 +151,7 @@ pub enum CheckCode {
     U007,
     U008,
     // pydocstyle
+    D400,
     D419,
     // Meta
     M001,
@@ -250,6 +251,7 @@ pub enum CheckKind {
     SuperCallWithParameters,
     // pydocstyle
     EmptyDocstring,
+    DocstringEndsInNonPeriod,
     // Meta
     UnusedNOQA(Option<Vec<String>>),
 }
@@ -359,6 +361,7 @@ impl CheckCode {
             CheckCode::U007 => CheckKind::UsePEP604Annotation,
             CheckCode::U008 => CheckKind::SuperCallWithParameters,
             // pydocstyle
+            CheckCode::D400 => CheckKind::DocstringEndsInNonPeriod,
             CheckCode::D419 => CheckKind::EmptyDocstring,
             // Meta
             CheckCode::M001 => CheckKind::UnusedNOQA(None),
@@ -448,6 +451,7 @@ impl CheckKind {
             CheckKind::UselessObjectInheritance(_) => &CheckCode::U004,
             CheckKind::SuperCallWithParameters => &CheckCode::U008,
             // pydocstyle
+            CheckKind::DocstringEndsInNonPeriod => &CheckCode::D400,
             CheckKind::EmptyDocstring => &CheckCode::D419,
             // Meta
             CheckKind::UnusedNOQA(_) => &CheckCode::M001,
@@ -693,6 +697,9 @@ impl CheckKind {
                 "Use `super()` instead of `super(__class__, self)`".to_string()
             }
             // pydocstyle
+            CheckKind::DocstringEndsInNonPeriod => {
+                "First line should end with a period".to_string()
+            }
             CheckKind::EmptyDocstring => "Docstring is empty".to_string(),
             // Meta
             CheckKind::UnusedNOQA(codes) => match codes {

src/docstrings.rs

@@ -61,8 +61,7 @@ pub fn extract<'a, 'b>(
     None
 }
 
-pub fn docstring_empty(checker: &mut Checker, docstring: &Docstring) {
-    // Extract the source.
+pub fn not_empty(checker: &mut Checker, docstring: &Docstring) {
     if let ExprKind::Constant {
         value: Constant::Str(string),
         ..
@@ -76,3 +75,20 @@ pub fn docstring_empty(checker: &mut Checker, docstring: &Docstring) {
         }
     }
 }
+
+pub fn ends_with_period(checker: &mut Checker, docstring: &Docstring) {
+    if let ExprKind::Constant {
+        value: Constant::Str(string),
+        ..
+    } = &docstring.expr.node
+    {
+        if let Some(string) = string.lines().next() {
+            if !string.ends_with('.') {
+                checker.add_check(Check::new(
+                    CheckKind::DocstringEndsInNonPeriod,
+                    Range::from_located(docstring.expr),
+                ));
+            }
+        }
+    }
+}

src/linter.rs

@@ -978,6 +978,18 @@ mod tests {
         Ok(())
     }
 
+    #[test]
+    fn d400() -> Result<()> {
+        let mut checks = check_path(
+            Path::new("./resources/test/fixtures/D400.py"),
+            &settings::Settings::for_rule(CheckCode::D400),
+            &fixer::Mode::Generate,
+        )?;
+        checks.sort_by_key(|check| check.location);
+        insta::assert_yaml_snapshot!(checks);
+        Ok(())
+    }
+
     #[test]
     fn d419() -> Result<()> {
         let mut checks = check_path(

src/snapshots/ruff__linter__tests__d400.snap

@@ -0,0 +1,21 @@
+---
+source: src/linter.rs
+expression: checks
+---
+- kind: DocstringEndsInPeriod
+  location:
+    row: 9
+    column: 6
+  end_location:
+    row: 12
+    column: 8
+  fix: ~
+- kind: DocstringEndsInPeriod
+  location:
+    row: 16
+    column: 6
+  end_location:
+    row: 19
+    column: 8
+  fix: ~
+

src/snapshots/ruff__linter__tests__d400.snap.new

@@ -0,0 +1,22 @@
+---
+source: src/linter.rs
+assertion_line: 989
+expression: checks
+---
+- kind: DocstringEndsInNonPeriod
+  location:
+    row: 9
+    column: 6
+  end_location:
+    row: 12
+    column: 8
+  fix: ~
+- kind: DocstringEndsInNonPeriod
+  location:
+    row: 16
+    column: 6
+  end_location:
+    row: 19
+    column: 8
+  fix: ~
+