[pylint] Implement bad-open-mode (W1501)

crates/ruff_linter/resources/test/fixtures/pylint/bad_open_mode.py

@@ -0,0 +1,34 @@
+import pathlib
+
+NAME = "foo.bar"
+open(NAME, "wb")
+open(NAME, "w", encoding="utf-8")
+open(NAME, "rb")
+open(NAME, "x", encoding="utf-8")
+open(NAME, "br")
+open(NAME, "+r", encoding="utf-8")
+open(NAME, "xb")
+open(NAME, "rwx")  # [bad-open-mode]
+open(NAME, mode="rwx")  # [bad-open-mode]
+open(NAME, "rwx", encoding="utf-8")  # [bad-open-mode]
+open(NAME, "rr", encoding="utf-8")  # [bad-open-mode]
+open(NAME, "+", encoding="utf-8")  # [bad-open-mode]
+open(NAME, "xw", encoding="utf-8")  # [bad-open-mode]
+open(NAME, "ab+")
+open(NAME, "a+b")
+open(NAME, "+ab")
+open(NAME, "+rUb")
+open(NAME, "x+b")
+open(NAME, "Ua", encoding="utf-8")  # [bad-open-mode]
+open(NAME, "Ur++", encoding="utf-8")  # [bad-open-mode]
+open(NAME, "Ut", encoding="utf-8")
+open(NAME, "Ubr")
+
+mode = "rw"
+open(NAME, mode)
+
+pathlib.Path(NAME).open("wb")
+pathlib.Path(NAME).open(mode)
+pathlib.Path(NAME).open("rwx")  # [bad-open-mode]
+pathlib.Path(NAME).open(mode="rwx")  # [bad-open-mode]
+pathlib.Path(NAME).open("rwx", encoding="utf-8")  # [bad-open-mode]

crates/ruff_linter/src/checkers/ast/analyze/expression.rs

@@ -749,6 +749,9 @@ pub(crate) fn expression(expr: &Expr, checker: &mut Checker) {
             if checker.enabled(Rule::SysExitAlias) {
                 pylint::rules::sys_exit_alias(checker, func);
             }
+            if checker.enabled(Rule::BadOpenMode) {
+                pylint::rules::bad_open_mode(checker, call);
+            }
             if checker.enabled(Rule::BadStrStripCall) {
                 pylint::rules::bad_str_strip_call(checker, func, args);
             }

crates/ruff_linter/src/codes.rs

@@ -270,6 +270,7 @@ pub fn code_to_rule(linter: Linter, code: &str) -> Option<(RuleGroup, Rule)> {
         (Pylint, "W0604") => (RuleGroup::Preview, rules::pylint::rules::GlobalAtModuleLevel),
         (Pylint, "W0603") => (RuleGroup::Stable, rules::pylint::rules::GlobalStatement),
         (Pylint, "W0711") => (RuleGroup::Stable, rules::pylint::rules::BinaryOpException),
+        (Pylint, "W1501") => (RuleGroup::Preview, rules::pylint::rules::BadOpenMode),
         (Pylint, "W1508") => (RuleGroup::Stable, rules::pylint::rules::InvalidEnvvarDefault),
         (Pylint, "W1509") => (RuleGroup::Stable, rules::pylint::rules::SubprocessPopenPreexecFn),
         (Pylint, "W1510") => (RuleGroup::Stable, rules::pylint::rules::SubprocessRunWithoutCheck),

crates/ruff_linter/src/rules/pylint/mod.rs

@@ -21,6 +21,7 @@ mod tests {
     #[test_case(Rule::AndOrTernary, Path::new("and_or_ternary.py"))]
     #[test_case(Rule::AssertOnStringLiteral, Path::new("assert_on_string_literal.py"))]
     #[test_case(Rule::AwaitOutsideAsync, Path::new("await_outside_async.py"))]
+    #[test_case(Rule::BadOpenMode, Path::new("bad_open_mode.py"))]
     #[test_case(
         Rule::BadStringFormatCharacter,
         Path::new("bad_string_format_character.py")

crates/ruff_linter/src/rules/pylint/rules/bad_open_mode.rs

@@ -0,0 +1,197 @@
+use bitflags::bitflags;
+
+use ruff_diagnostics::{Diagnostic, Violation};
+use ruff_macros::{derive_message_formats, violation};
+use ruff_python_ast::{self as ast, Constant, Expr};
+use ruff_python_semantic::SemanticModel;
+use ruff_text_size::Ranged;
+
+use crate::checkers::ast::Checker;
+
+/// ## What it does
+/// Check for an invalid `mode` argument in `open` calls.
+///
+/// ## Why is this bad?
+/// The `open` function accepts a `mode` argument that specifies how the file
+/// should be opened (e.g., read-only, write-only, append-only, etc.).
+///
+/// Python supports a variety of open modes: `r`, `w`, `a`, and `x`, to control
+/// reading, writing, appending, and creating, respectively, along with
+/// `b` (binary mode), `+` (read and write), and `U` (universal newlines),
+/// the latter of which is only valid alongside `r`. This rule detects both
+/// invalid combinations of modes and invalid characters in the mode string
+/// itself.
+///
+/// ## Example
+/// ```python
+/// with open("file", "rwx") as f:
+///     return f.read()
+/// ```
+///
+/// Use instead:
+/// ```python
+/// with open("file", "r") as f:
+///     return f.read()
+/// ```
+///
+/// ## References
+/// - [Python documentation: `open`](https://docs.python.org/3/library/functions.html#open)
+#[violation]
+pub struct BadOpenMode {
+    mode: String,
+}
+
+impl Violation for BadOpenMode {
+    #[derive_message_formats]
+    fn message(&self) -> String {
+        let BadOpenMode { mode } = self;
+        format!("`{mode}` is not a valid mode for `open`")
+    }
+}
+
+/// PLW1501
+pub(crate) fn bad_open_mode(checker: &mut Checker, call: &ast::ExprCall) {
+    let Some(kind) = is_open(call.func.as_ref(), checker.semantic()) else {
+        return;
+    };
+
+    let Some(mode) = extract_mode(call, kind) else {
+        return;
+    };
+
+    let Expr::Constant(ast::ExprConstant {
+        value: Constant::Str(ast::StringConstant { value, .. }),
+        ..
+    }) = mode
+    else {
+        return;
+    };
+
+    if is_valid_mode(value) {
+        return;
+    }
+
+    checker.diagnostics.push(Diagnostic::new(
+        BadOpenMode {
+            mode: value.to_string(),
+        },
+        mode.range(),
+    ));
+}
+
+#[derive(Debug, Copy, Clone)]
+enum Kind {
+    /// A call to the builtin `open(...)`.
+    Builtin,
+    /// A call to `pathlib.Path(...).open(...)`.
+    Pathlib,
+}
+
+/// If a function is a call to `open`, returns the kind of `open` call.
+fn is_open(func: &Expr, semantic: &SemanticModel) -> Option<Kind> {
+    match func {
+        // Ex) `pathlib.Path(...).open(...)`
+        Expr::Attribute(ast::ExprAttribute { attr, value, .. }) if attr.as_str() == "open" => {
+            match value.as_ref() {
+                Expr::Call(ast::ExprCall { func, .. }) => semantic
+                    .resolve_call_path(func)
+                    .is_some_and(|call_path| matches!(call_path.as_slice(), ["pathlib", "Path"]))
+                    .then_some(Kind::Pathlib),
+                _ => None,
+            }
+        }
+        // Ex) `open(...)`
+        Expr::Name(ast::ExprName { id, .. }) => {
+            (id.as_str() == "open" && semantic.is_builtin("open")).then_some(Kind::Builtin)
+        }
+        _ => None,
+    }
+}
+
+/// Returns the mode argument, if present.
+fn extract_mode(call: &ast::ExprCall, kind: Kind) -> Option<&Expr> {
+    match kind {
+        Kind::Builtin => call.arguments.find_argument("mode", 1),
+        Kind::Pathlib => call.arguments.find_argument("mode", 0),
+    }
+}
+
+bitflags! {
+    #[derive(Copy, Clone, Debug, PartialEq, Eq)]
+    pub(super) struct OpenMode: u8 {
+        /// `r`
+        const READ = 0b0001;
+        /// `w`
+        const WRITE = 0b0010;
+        /// `a`
+        const APPEND = 0b0100;
+        /// `x`
+        const CREATE = 0b1000;
+        /// `b`
+        const BINARY = 0b10000;
+        /// `t`
+        const TEXT = 0b10_0000;
+        /// `+`
+        const PLUS = 0b100_0000;
+        /// `U`
+        const UNIVERSAL_NEWLINES = 0b1000_0000;
+
+    }
+}
+
+impl TryFrom<char> for OpenMode {
+    type Error = ();
+
+    fn try_from(value: char) -> Result<Self, Self::Error> {
+        match value {
+            'r' => Ok(Self::READ),
+            'w' => Ok(Self::WRITE),
+            'a' => Ok(Self::APPEND),
+            'x' => Ok(Self::CREATE),
+            'b' => Ok(Self::BINARY),
+            't' => Ok(Self::TEXT),
+            '+' => Ok(Self::PLUS),
+            'U' => Ok(Self::UNIVERSAL_NEWLINES),
+            _ => Err(()),
+        }
+    }
+}
+
+/// Returns `true` if the open mode is valid.
+fn is_valid_mode(mode: &str) -> bool {
+    // Flag duplicates and invalid characters.
+    let mut flags = OpenMode::empty();
+    for char in mode.chars() {
+        let Ok(flag) = OpenMode::try_from(char) else {
+            return false;
+        };
+        if flags.intersects(flag) {
+            return false;
+        }
+        flags.insert(flag);
+    }
+
+    // Both text and binary mode cannot be set at the same time.
+    if flags.contains(OpenMode::TEXT | OpenMode::BINARY) {
+        return false;
+    }
+
+    // The `U` mode is only valid with `r`.
+    if flags.contains(OpenMode::UNIVERSAL_NEWLINES)
+        && flags.intersects(OpenMode::WRITE | OpenMode::APPEND | OpenMode::CREATE)
+    {
+        return false;
+    }
+
+    // Otherwise, reading, writing, creating, and appending are mutually exclusive.
+    [
+        OpenMode::READ | OpenMode::UNIVERSAL_NEWLINES,
+        OpenMode::WRITE,
+        OpenMode::CREATE,
+        OpenMode::APPEND,
+    ]
+    .into_iter()
+    .filter(|flag| flags.intersects(*flag))
+    .count()
+        == 1
+}

crates/ruff_linter/src/rules/pylint/rules/mod.rs

@@ -2,6 +2,7 @@ pub(crate) use and_or_ternary::*;
 pub(crate) use assert_on_string_literal::*;
 pub(crate) use await_outside_async::*;
 pub(crate) use bad_dunder_method_name::*;
+pub(crate) use bad_open_mode::*;
 pub(crate) use bad_str_strip_call::*;
 pub(crate) use bad_string_format_character::BadStringFormatCharacter;
 pub(crate) use bad_string_format_type::*;
@@ -70,6 +71,7 @@ mod and_or_ternary;
 mod assert_on_string_literal;
 mod await_outside_async;
 mod bad_dunder_method_name;
+mod bad_open_mode;
 mod bad_str_strip_call;
 pub(crate) mod bad_string_format_character;
 mod bad_string_format_type;

crates/ruff_linter/src/rules/pylint/snapshots/ruff_linter__rules__pylint__tests__PLW1501_bad_open_mode.py.snap

@@ -0,0 +1,111 @@
+---
+source: crates/ruff_linter/src/rules/pylint/mod.rs
+---
+bad_open_mode.py:11:12: PLW1501 `rwx` is not a valid mode for `open`
+   |
+ 9 | open(NAME, "+r", encoding="utf-8")
+10 | open(NAME, "xb")
+11 | open(NAME, "rwx")  # [bad-open-mode]
+   |            ^^^^^ PLW1501
+12 | open(NAME, mode="rwx")  # [bad-open-mode]
+13 | open(NAME, "rwx", encoding="utf-8")  # [bad-open-mode]
+   |
+
+bad_open_mode.py:12:17: PLW1501 `rwx` is not a valid mode for `open`
+   |
+10 | open(NAME, "xb")
+11 | open(NAME, "rwx")  # [bad-open-mode]
+12 | open(NAME, mode="rwx")  # [bad-open-mode]
+   |                 ^^^^^ PLW1501
+13 | open(NAME, "rwx", encoding="utf-8")  # [bad-open-mode]
+14 | open(NAME, "rr", encoding="utf-8")  # [bad-open-mode]
+   |
+
+bad_open_mode.py:13:12: PLW1501 `rwx` is not a valid mode for `open`
+   |
+11 | open(NAME, "rwx")  # [bad-open-mode]
+12 | open(NAME, mode="rwx")  # [bad-open-mode]
+13 | open(NAME, "rwx", encoding="utf-8")  # [bad-open-mode]
+   |            ^^^^^ PLW1501
+14 | open(NAME, "rr", encoding="utf-8")  # [bad-open-mode]
+15 | open(NAME, "+", encoding="utf-8")  # [bad-open-mode]
+   |
+
+bad_open_mode.py:14:12: PLW1501 `rr` is not a valid mode for `open`
+   |
+12 | open(NAME, mode="rwx")  # [bad-open-mode]
+13 | open(NAME, "rwx", encoding="utf-8")  # [bad-open-mode]
+14 | open(NAME, "rr", encoding="utf-8")  # [bad-open-mode]
+   |            ^^^^ PLW1501
+15 | open(NAME, "+", encoding="utf-8")  # [bad-open-mode]
+16 | open(NAME, "xw", encoding="utf-8")  # [bad-open-mode]
+   |
+
+bad_open_mode.py:15:12: PLW1501 `+` is not a valid mode for `open`
+   |
+13 | open(NAME, "rwx", encoding="utf-8")  # [bad-open-mode]
+14 | open(NAME, "rr", encoding="utf-8")  # [bad-open-mode]
+15 | open(NAME, "+", encoding="utf-8")  # [bad-open-mode]
+   |            ^^^ PLW1501
+16 | open(NAME, "xw", encoding="utf-8")  # [bad-open-mode]
+17 | open(NAME, "ab+")
+   |
+
+bad_open_mode.py:16:12: PLW1501 `xw` is not a valid mode for `open`
+   |
+14 | open(NAME, "rr", encoding="utf-8")  # [bad-open-mode]
+15 | open(NAME, "+", encoding="utf-8")  # [bad-open-mode]
+16 | open(NAME, "xw", encoding="utf-8")  # [bad-open-mode]
+   |            ^^^^ PLW1501
+17 | open(NAME, "ab+")
+18 | open(NAME, "a+b")
+   |
+
+bad_open_mode.py:22:12: PLW1501 `Ua` is not a valid mode for `open`
+   |
+20 | open(NAME, "+rUb")
+21 | open(NAME, "x+b")
+22 | open(NAME, "Ua", encoding="utf-8")  # [bad-open-mode]
+   |            ^^^^ PLW1501
+23 | open(NAME, "Ur++", encoding="utf-8")  # [bad-open-mode]
+24 | open(NAME, "Ut", encoding="utf-8")
+   |
+
+bad_open_mode.py:23:12: PLW1501 `Ur++` is not a valid mode for `open`
+   |
+21 | open(NAME, "x+b")
+22 | open(NAME, "Ua", encoding="utf-8")  # [bad-open-mode]
+23 | open(NAME, "Ur++", encoding="utf-8")  # [bad-open-mode]
+   |            ^^^^^^ PLW1501
+24 | open(NAME, "Ut", encoding="utf-8")
+25 | open(NAME, "Ubr")
+   |
+
+bad_open_mode.py:32:25: PLW1501 `rwx` is not a valid mode for `open`
+   |
+30 | pathlib.Path(NAME).open("wb")
+31 | pathlib.Path(NAME).open(mode)
+32 | pathlib.Path(NAME).open("rwx")  # [bad-open-mode]
+   |                         ^^^^^ PLW1501
+33 | pathlib.Path(NAME).open(mode="rwx")  # [bad-open-mode]
+34 | pathlib.Path(NAME).open("rwx", encoding="utf-8")  # [bad-open-mode]
+   |
+
+bad_open_mode.py:33:30: PLW1501 `rwx` is not a valid mode for `open`
+   |
+31 | pathlib.Path(NAME).open(mode)
+32 | pathlib.Path(NAME).open("rwx")  # [bad-open-mode]
+33 | pathlib.Path(NAME).open(mode="rwx")  # [bad-open-mode]
+   |                              ^^^^^ PLW1501
+34 | pathlib.Path(NAME).open("rwx", encoding="utf-8")  # [bad-open-mode]
+   |
+
+bad_open_mode.py:34:25: PLW1501 `rwx` is not a valid mode for `open`
+   |
+32 | pathlib.Path(NAME).open("rwx")  # [bad-open-mode]
+33 | pathlib.Path(NAME).open(mode="rwx")  # [bad-open-mode]
+34 | pathlib.Path(NAME).open("rwx", encoding="utf-8")  # [bad-open-mode]
+   |                         ^^^^^ PLW1501
+   |
+
+