Implement PYI048 for `flake8-pyi` plugin (#4645)

crates/ruff/resources/test/fixtures/flake8_pyi/PYI048.py

@@ -0,0 +1,19 @@
+def bar():    # OK
+    ...
+
+
+def oof():    # OK, docstrings are handled by another rule
+    """oof"""
+    print("foo")
+
+
+def foo():    # Ok not in Stub file
+    """foo"""
+    print("foo")
+    print("foo")
+
+
+def buzz():    # Ok not in Stub file
+    print("fizz")
+    print("buzz")
+    print("test")

crates/ruff/resources/test/fixtures/flake8_pyi/PYI048.pyi

@@ -0,0 +1,20 @@
+def bar():
+    ...  # OK
+
+
+def oof():   # OK, docstrings are handled by another rule
+  """oof"""
+  print("foo")
+
+
+
+def foo():   # ERROR PYI048
+    """foo"""
+    print("foo")
+    print("foo")
+
+
+def buzz():   # ERROR PYI048
+    print("fizz")
+    print("buzz")
+    print("test")

crates/ruff/src/checkers/ast/mod.rs

@@ -425,6 +425,9 @@ where
                     if self.enabled(Rule::NonEmptyStubBody) {
                         flake8_pyi::rules::non_empty_stub_body(self, body);
                     }
+                    if self.enabled(Rule::StubBodyMultipleStatements) {
+                        flake8_pyi::rules::stub_body_multiple_statements(self, stmt, body);
+                    }
                 }
 
                 if self.enabled(Rule::DunderFunctionName) {

crates/ruff/src/codes.rs

@@ -592,6 +592,7 @@ pub fn code_to_rule(linter: Linter, code: &str) -> Option<(RuleGroup, Rule)> {
         (Flake8Pyi, "033") => (RuleGroup::Unspecified, Rule::TypeCommentInStub),
         (Flake8Pyi, "042") => (RuleGroup::Unspecified, Rule::SnakeCaseTypeAlias),
         (Flake8Pyi, "043") => (RuleGroup::Unspecified, Rule::TSuffixedTypeAlias),
+        (Flake8Pyi, "048") => (RuleGroup::Unspecified, Rule::StubBodyMultipleStatements),
         (Flake8Pyi, "052") => (RuleGroup::Unspecified, Rule::UnannotatedAssignmentInStub),
 
         // flake8-pytest-style

crates/ruff/src/registry.rs

@@ -519,6 +519,7 @@ ruff_macros::register_rules!(
     rules::flake8_pyi::rules::PassStatementStubBody,
     rules::flake8_pyi::rules::QuotedAnnotationInStub,
     rules::flake8_pyi::rules::SnakeCaseTypeAlias,
+    rules::flake8_pyi::rules::StubBodyMultipleStatements,
     rules::flake8_pyi::rules::TSuffixedTypeAlias,
     rules::flake8_pyi::rules::TypeCommentInStub,
     rules::flake8_pyi::rules::TypedArgumentDefaultInStub,

crates/ruff/src/rules/flake8_pyi/mod.rs

@@ -34,6 +34,8 @@ mod tests {
     #[test_case(Rule::QuotedAnnotationInStub, Path::new("PYI020.pyi"))]
     #[test_case(Rule::SnakeCaseTypeAlias, Path::new("PYI042.py"))]
     #[test_case(Rule::SnakeCaseTypeAlias, Path::new("PYI042.pyi"))]
+    #[test_case(Rule::StubBodyMultipleStatements, Path::new("PYI048.py"))]
+    #[test_case(Rule::StubBodyMultipleStatements, Path::new("PYI048.pyi"))]
     #[test_case(Rule::TSuffixedTypeAlias, Path::new("PYI043.py"))]
     #[test_case(Rule::TSuffixedTypeAlias, Path::new("PYI043.pyi"))]
     #[test_case(Rule::TypeCommentInStub, Path::new("PYI033.py"))]

crates/ruff/src/rules/flake8_pyi/rules/mod.rs

@@ -16,6 +16,9 @@ pub(crate) use simple_defaults::{
     typed_argument_simple_defaults, unannotated_assignment_in_stub, ArgumentDefaultInStub,
     AssignmentDefaultInStub, TypedArgumentDefaultInStub, UnannotatedAssignmentInStub,
 };
+pub(crate) use stub_body_multiple_statements::{
+    stub_body_multiple_statements, StubBodyMultipleStatements,
+};
 pub(crate) use type_alias_naming::{
     snake_case_type_alias, t_suffixed_type_alias, SnakeCaseTypeAlias, TSuffixedTypeAlias,
 };
@@ -34,6 +37,7 @@ mod pass_statement_stub_body;
 mod prefix_type_params;
 mod quoted_annotation_in_stub;
 mod simple_defaults;
+mod stub_body_multiple_statements;
 mod type_alias_naming;
 mod type_comment_in_stub;
 mod unrecognized_platform;

crates/ruff/src/rules/flake8_pyi/rules/stub_body_multiple_statements.rs

@@ -0,0 +1,37 @@
+use rustpython_parser::ast::Stmt;
+
+use ruff_diagnostics::{Diagnostic, Violation};
+use ruff_macros::{derive_message_formats, violation};
+use ruff_python_ast::helpers;
+use ruff_python_ast::helpers::is_docstring_stmt;
+
+use crate::checkers::ast::Checker;
+
+#[violation]
+pub struct StubBodyMultipleStatements;
+
+impl Violation for StubBodyMultipleStatements {
+    #[derive_message_formats]
+    fn message(&self) -> String {
+        format!("Function body must contain exactly one statement")
+    }
+}
+
+/// PYI010
+pub(crate) fn stub_body_multiple_statements(checker: &mut Checker, stmt: &Stmt, body: &[Stmt]) {
+    // If the function body consists of exactly one statement, abort.
+    if body.len() == 1 {
+        return;
+    }
+
+    // If the function body consists of exactly two statements, and the first is a
+    // docstring, abort (this is covered by PYI021).
+    if body.len() == 2 && is_docstring_stmt(&body[0]) {
+        return;
+    }
+
+    checker.diagnostics.push(Diagnostic::new(
+        StubBodyMultipleStatements,
+        helpers::identifier_range(stmt, checker.locator),
+    ));
+}

crates/ruff/src/rules/flake8_pyi/snapshots/ruff__rules__flake8_pyi__tests__PYI048_PYI048.py.snap

@@ -0,0 +1,4 @@
+---
+source: crates/ruff/src/rules/flake8_pyi/mod.rs
+---
+

crates/ruff/src/rules/flake8_pyi/snapshots/ruff__rules__flake8_pyi__tests__PYI048_PYI048.pyi.snap

@@ -0,0 +1,20 @@
+---
+source: crates/ruff/src/rules/flake8_pyi/mod.rs
+---
+PYI048.pyi:11:5: PYI048 Function body must contain exactly one statement
+   |
+11 | def foo():   # ERROR PYI048
+   |     ^^^ PYI048
+12 |     """foo"""
+13 |     print("foo")
+   |
+
+PYI048.pyi:17:5: PYI048 Function body must contain exactly one statement
+   |
+17 | def buzz():   # ERROR PYI048
+   |     ^^^^ PYI048
+18 |     print("fizz")
+19 |     print("buzz")
+   |
+
+

ruff.schema.json

@@ -2206,6 +2206,7 @@
         "PYI04",
         "PYI042",
         "PYI043",
+        "PYI048",
         "PYI05",
         "PYI052",
         "Q",