[flake8-use-pathlib] Implement path-constructor-default-argument …

…(`PTH201`) (#5833)

Reviving #2348 step by step

Pt 2. PTH201: Path Constructor Default Argument

- rule originates from `refurb`:
#1348
- Using PTH201 rather than FURBXXX to keep all pathlib logic together

crates/ruff/resources/test/fixtures/flake8_use_pathlib/PTH201.py

@@ -0,0 +1,14 @@
+from pathlib import Path, PurePath
+from pathlib import Path as pth
+
+# match
+_ = Path(".")
+_ = pth(".")
+_ = PurePath(".")
+
+# no match
+_ = Path()
+print(".")
+Path("file.txt")
+Path(".", "folder")
+PurePath(".", "folder")

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

@@ -3027,6 +3027,9 @@ where
                 ]) {
                     flake8_use_pathlib::rules::replaceable_by_pathlib(self, func);
                 }
+                if self.enabled(Rule::PathConstructorCurrentDirectory) {
+                    flake8_use_pathlib::rules::path_constructor_current_directory(self, expr, func);
+                }
                 if self.enabled(Rule::NumpyLegacyRandom) {
                     numpy::rules::legacy_random(self, func);
                 }

crates/ruff/src/codes.rs

@@ -748,6 +748,7 @@ pub fn code_to_rule(linter: Linter, code: &str) -> Option<(RuleGroup, Rule)> {
         (Flake8UsePathlib, "122") => (RuleGroup::Unspecified, rules::flake8_use_pathlib::violations::OsPathSplitext),
         (Flake8UsePathlib, "123") => (RuleGroup::Unspecified, rules::flake8_use_pathlib::violations::BuiltinOpen),
         (Flake8UsePathlib, "124") => (RuleGroup::Unspecified, rules::flake8_use_pathlib::violations::PyPath),
+        (Flake8UsePathlib, "201") => (RuleGroup::Unspecified, rules::flake8_use_pathlib::rules::PathConstructorCurrentDirectory),
 
         // flake8-logging-format
         (Flake8LoggingFormat, "001") => (RuleGroup::Unspecified, rules::flake8_logging_format::violations::LoggingStringFormat),

crates/ruff/src/rules/flake8_use_pathlib/mod.rs

@@ -56,6 +56,8 @@ mod tests {
 
     #[test_case(Rule::PyPath, Path::new("py_path_1.py"))]
     #[test_case(Rule::PyPath, Path::new("py_path_2.py"))]
+    #[test_case(Rule::PathConstructorCurrentDirectory, Path::new("PTH201.py"))]
+
     fn rules_pypath(rule_code: Rule, path: &Path) -> Result<()> {
         let snapshot = format!("{}_{}", rule_code.noqa_code(), path.to_string_lossy());
         let diagnostics = test_path(

crates/ruff/src/rules/flake8_use_pathlib/rules/mod.rs

@@ -1,3 +1,5 @@
+pub(crate) use path_constructor_current_directory::*;
 pub(crate) use replaceable_by_pathlib::*;
 
+mod path_constructor_current_directory;
 mod replaceable_by_pathlib;

crates/ruff/src/rules/flake8_use_pathlib/rules/path_constructor_current_directory.rs

@@ -0,0 +1,85 @@
+use rustpython_parser::ast::{Constant, Expr, ExprCall, ExprConstant};
+
+use ruff_diagnostics::{AlwaysAutofixableViolation, Diagnostic, Edit, Fix};
+use ruff_macros::{derive_message_formats, violation};
+
+use crate::checkers::ast::Checker;
+use crate::registry::AsRule;
+
+/// ## What it does
+/// Checks for `pathlib.Path` objects that are initialized with the current
+/// directory.
+///
+/// ## Why is this bad?
+/// The `Path()` constructor defaults to the current directory, so passing it
+/// in explicitly (as `"."`) is unnecessary.
+///
+/// ## Example
+/// ```python
+/// from pathlib import Path
+///
+/// _ = Path(".")
+/// ```
+///
+/// Use instead:
+/// ```python
+/// from pathlib import Path
+///
+/// _ = Path()
+/// ```
+///
+/// ## References
+/// - [Python documentation: `Path`](https://docs.python.org/3/library/pathlib.html#pathlib.Path)
+#[violation]
+pub struct PathConstructorCurrentDirectory;
+
+impl AlwaysAutofixableViolation for PathConstructorCurrentDirectory {
+    #[derive_message_formats]
+    fn message(&self) -> String {
+        format!("Do not pass the current directory explicitly to `Path`")
+    }
+
+    fn autofix_title(&self) -> String {
+        "Remove the current directory argument".to_string()
+    }
+}
+
+/// PTH201
+pub(crate) fn path_constructor_current_directory(checker: &mut Checker, expr: &Expr, func: &Expr) {
+    if !checker
+        .semantic()
+        .resolve_call_path(func)
+        .map_or(false, |call_path| {
+            matches!(call_path.as_slice(), ["pathlib", "Path" | "PurePath"])
+        })
+    {
+        return;
+    }
+
+    let Expr::Call(ExprCall { args, keywords, .. }) = expr else {
+        return;
+    };
+
+    if !keywords.is_empty() {
+        return;
+    }
+
+    let [Expr::Constant(ExprConstant {
+        value: Constant::Str(value),
+        kind: _,
+        range
+    })] = args.as_slice()
+    else {
+        return;
+    };
+
+    if value != "." {
+        return;
+    }
+
+    let mut diagnostic = Diagnostic::new(PathConstructorCurrentDirectory, *range);
+    if checker.patch(diagnostic.kind.rule()) {
+        diagnostic.set_fix(Fix::automatic(Edit::range_deletion(*range)));
+    }
+    checker.diagnostics.push(diagnostic);
+}

crates/ruff/src/rules/flake8_use_pathlib/snapshots/ruff__rules__flake8_use_pathlib__tests__PTH201_PTH201.py.snap

@@ -0,0 +1,65 @@
+---
+source: crates/ruff/src/rules/flake8_use_pathlib/mod.rs
+---
+PTH201.py:5:10: PTH201 [*] Do not pass the current directory explicitly to `Path`
+  |
+4 | # match
+5 | _ = Path(".")
+  |          ^^^ PTH201
+6 | _ = pth(".")
+7 | _ = PurePath(".")
+  |
+  = help: Remove the current directory argument
+
+ℹ Fix
+2 2 | from pathlib import Path as pth
+3 3 | 
+4 4 | # match
+5   |-_ = Path(".")
+  5 |+_ = Path()
+6 6 | _ = pth(".")
+7 7 | _ = PurePath(".")
+8 8 | 
+
+PTH201.py:6:9: PTH201 [*] Do not pass the current directory explicitly to `Path`
+  |
+4 | # match
+5 | _ = Path(".")
+6 | _ = pth(".")
+  |         ^^^ PTH201
+7 | _ = PurePath(".")
+  |
+  = help: Remove the current directory argument
+
+ℹ Fix
+3 3 | 
+4 4 | # match
+5 5 | _ = Path(".")
+6   |-_ = pth(".")
+  6 |+_ = pth()
+7 7 | _ = PurePath(".")
+8 8 | 
+9 9 | # no match
+
+PTH201.py:7:14: PTH201 [*] Do not pass the current directory explicitly to `Path`
+  |
+5 | _ = Path(".")
+6 | _ = pth(".")
+7 | _ = PurePath(".")
+  |              ^^^ PTH201
+8 | 
+9 | # no match
+  |
+  = help: Remove the current directory argument
+
+ℹ Fix
+4 4 | # match
+5 5 | _ = Path(".")
+6 6 | _ = pth(".")
+7   |-_ = PurePath(".")
+  7 |+_ = PurePath()
+8 8 | 
+9 9 | # no match
+10 10 | _ = Path()
+
+