[ruff] Ambiguous pattern passed to pytest.raises() (RUF043)

crates/ruff_linter/resources/test/fixtures/ruff/RUF043.py

@@ -0,0 +1,91 @@
+import re
+import pytest
+
+def test_foo():
+
+    ### Errors
+
+    with pytest.raises(FooAtTheEnd, match="foo."): ...
+    with pytest.raises(PackageExtraSpecifier, match="Install `foo[bar]` to enjoy all features"): ...
+    with pytest.raises(InnocentQuestion, match="Did you mean to use `Literal` instead?"): ...
+
+    with pytest.raises(StringConcatenation, match="Huh"
+                                                  "?"): ...
+    with pytest.raises(ManuallyEscapedWindowsPathToDotFile, match="C:\\\\Users\\\\Foo\\\\.config"): ...
+
+    with pytest.raises(MiddleDot, match="foo.bar"): ...
+    with pytest.raises(EndDot, match="foobar."): ...
+    with pytest.raises(EscapedFollowedByUnescaped, match="foo\\.*bar"): ...
+    with pytest.raises(UnescapedFollowedByEscaped, match="foo.\\*bar"): ...
+
+
+    ## Metasequences
+
+    with pytest.raises(StartOfInput, match="foo\\Abar"): ...
+    with pytest.raises(WordBoundary, match="foo\\bbar"): ...
+    with pytest.raises(NonWordBoundary, match="foo\\Bbar"): ...
+    with pytest.raises(Digit, match="foo\\dbar"): ...
+    with pytest.raises(NonDigit, match="foo\\Dbar"): ...
+    with pytest.raises(Whitespace, match="foo\\sbar"): ...
+    with pytest.raises(NonWhitespace, match="foo\\Sbar"): ...
+    with pytest.raises(WordCharacter, match="foo\\wbar"): ...
+    with pytest.raises(NonWordCharacter, match="foo\\Wbar"): ...
+    with pytest.raises(EndOfInput, match="foo\\zbar"): ...
+
+    with pytest.raises(StartOfInput2, match="foobar\\A"): ...
+    with pytest.raises(WordBoundary2, match="foobar\\b"): ...
+    with pytest.raises(NonWordBoundary2, match="foobar\\B"): ...
+    with pytest.raises(Digit2, match="foobar\\d"): ...
+    with pytest.raises(NonDigit2, match="foobar\\D"): ...
+    with pytest.raises(Whitespace2, match="foobar\\s"): ...
+    with pytest.raises(NonWhitespace2, match="foobar\\S"): ...
+    with pytest.raises(WordCharacter2, match="foobar\\w"): ...
+    with pytest.raises(NonWordCharacter2, match="foobar\\W"): ...
+    with pytest.raises(EndOfInput2, match="foobar\\z"): ...
+
+
+    ### Acceptable false positives
+
+    with pytest.raises(NameEscape, match="\\N{EN DASH}"): ...
+
+
+    ### No errors
+
+    with pytest.raises(NoMatch): ...
+    with pytest.raises(NonLiteral, match=pattern): ...
+    with pytest.raises(FunctionCall, match=frobnicate("qux")): ...
+    with pytest.raises(ReEscaped, match=re.escape("foobar")): ...
+    with pytest.raises(RawString, match=r"fo()bar"): ...
+    with pytest.raises(RawStringPart, match=r"foo" '\bar'): ...
+    with pytest.raises(NoMetacharacters, match="foobar"): ...
+    with pytest.raises(EndBackslash, match="foobar\\"): ...
+
+    with pytest.raises(ManuallyEscaped, match="some\\.fully\\.qualified\\.name"): ...
+    with pytest.raises(ManuallyEscapedWindowsPath, match="C:\\\\Users\\\\Foo\\\\file\\.py"): ...
+
+    with pytest.raises(MiddleEscapedDot, match="foo\\.bar"): ...
+    with pytest.raises(MiddleEscapedBackslash, match="foo\\\\bar"): ...
+    with pytest.raises(EndEscapedDot, match="foobar\\."): ...
+    with pytest.raises(EndEscapedBackslash, match="foobar\\\\"): ...
+
+
+    ## Not-so-special metasequences
+
+    with pytest.raises(Alert, match="\\f"): ...
+    with pytest.raises(FormFeed, match="\\f"): ...
+    with pytest.raises(Newline, match="\\n"): ...
+    with pytest.raises(CarriageReturn, match="\\r"): ...
+    with pytest.raises(Tab, match="\\t"): ...
+    with pytest.raises(VerticalTab, match="\\v"): ...
+    with pytest.raises(HexEscape, match="\\xFF"): ...
+    with pytest.raises(_16BitUnicodeEscape, match="\\FFFF"): ...
+    with pytest.raises(_32BitUnicodeEscape, match="\\0010FFFF"): ...
+
+    ## Escaped metasequences
+
+    with pytest.raises(Whitespace, match="foo\\\\sbar"): ...
+    with pytest.raises(NonWhitespace, match="foo\\\\Sbar"): ...
+
+    ## Work by accident
+
+    with pytest.raises(OctalEscape, match="\\042"): ...

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

@@ -1105,6 +1105,9 @@ pub(crate) fn expression(expr: &Expr, checker: &mut Checker) {
             if checker.enabled(Rule::BatchedWithoutExplicitStrict) {
                 flake8_bugbear::rules::batched_without_explicit_strict(checker, call);
             }
+            if checker.enabled(Rule::PytestRaisesAmbiguousPattern) {
+                ruff::rules::pytest_raises_ambiguous_pattern(checker, call);
+            }
         }
         Expr::Dict(dict) => {
             if checker.any_enabled(&[

crates/ruff_linter/src/codes.rs

@@ -985,6 +985,7 @@ pub fn code_to_rule(linter: Linter, code: &str) -> Option<(RuleGroup, Rule)> {
         (Ruff, "039") => (RuleGroup::Preview, rules::ruff::rules::UnrawRePattern),
         (Ruff, "040") => (RuleGroup::Preview, rules::ruff::rules::InvalidAssertMessageLiteralArgument),
         (Ruff, "041") => (RuleGroup::Preview, rules::ruff::rules::UnnecessaryNestedLiteral),
+        (Ruff, "043") => (RuleGroup::Preview, rules::ruff::rules::PytestRaisesAmbiguousPattern),
         (Ruff, "046") => (RuleGroup::Preview, rules::ruff::rules::UnnecessaryCastToInt),
         (Ruff, "048") => (RuleGroup::Preview, rules::ruff::rules::MapIntVersionParsing),
         (Ruff, "051") => (RuleGroup::Preview, rules::ruff::rules::IfKeyInDictDel),

crates/ruff_linter/src/rules/flake8_pytest_style/rules/assertion.rs

@@ -144,7 +144,7 @@ impl Violation for PytestAssertInExcept {
 ///     ...
 /// ```
 ///
-/// References
+/// ## References
 /// - [`pytest` documentation: `pytest.fail`](https://docs.pytest.org/en/latest/reference/reference.html#pytest-fail)
 #[derive(ViolationMetadata)]
 pub(crate) struct PytestAssertAlwaysFalse;

crates/ruff_linter/src/rules/flake8_pytest_style/rules/marks.rs

@@ -104,7 +104,6 @@ impl AlwaysFixableViolation for PytestIncorrectMarkParenthesesStyle {
 ///
 /// ## References
 /// - [`pytest` documentation: `pytest.mark.usefixtures`](https://docs.pytest.org/en/latest/reference/reference.html#pytest-mark-usefixtures)
-
 #[derive(ViolationMetadata)]
 pub(crate) struct PytestUseFixturesWithoutParameters;
 

crates/ruff_linter/src/rules/flake8_pytest_style/rules/raises.rs

@@ -151,7 +151,7 @@ impl Violation for PytestRaisesWithoutException {
     }
 }
 
-fn is_pytest_raises(func: &Expr, semantic: &SemanticModel) -> bool {
+pub(crate) fn is_pytest_raises(func: &Expr, semantic: &SemanticModel) -> bool {
     semantic
         .resolve_qualified_name(func)
         .is_some_and(|qualified_name| matches!(qualified_name.segments(), ["pytest", "raises"]))

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

@@ -415,6 +415,7 @@ mod tests {
     #[test_case(Rule::UnnecessaryRegularExpression, Path::new("RUF055_0.py"))]
     #[test_case(Rule::UnnecessaryRegularExpression, Path::new("RUF055_1.py"))]
     #[test_case(Rule::UnnecessaryCastToInt, Path::new("RUF046.py"))]
+    #[test_case(Rule::PytestRaisesAmbiguousPattern, Path::new("RUF043.py"))]
     fn preview_rules(rule_code: Rule, path: &Path) -> Result<()> {
         let snapshot = format!(
             "preview__{}_{}",

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

@@ -23,6 +23,7 @@ pub(crate) use never_union::*;
 pub(crate) use none_not_at_end_of_union::*;
 pub(crate) use parenthesize_chained_operators::*;
 pub(crate) use post_init_default::*;
+pub(crate) use pytest_raises_ambiguous_pattern::*;
 pub(crate) use quadratic_list_summation::*;
 pub(crate) use redirected_noqa::*;
 pub(crate) use redundant_bool_literal::*;
@@ -71,6 +72,7 @@ mod never_union;
 mod none_not_at_end_of_union;
 mod parenthesize_chained_operators;
 mod post_init_default;
+mod pytest_raises_ambiguous_pattern;
 mod quadratic_list_summation;
 mod redirected_noqa;
 mod redundant_bool_literal;

crates/ruff_linter/src/rules/ruff/rules/pytest_raises_ambiguous_pattern.rs

@@ -0,0 +1,155 @@
+use crate::checkers::ast::Checker;
+use crate::rules::flake8_pytest_style::rules::is_pytest_raises;
+use ruff_diagnostics::{Diagnostic, Violation};
+use ruff_macros::{derive_message_formats, ViolationMetadata};
+use ruff_python_ast as ast;
+
+/// ## What it does
+/// Checks for non-raw literal string arguments passed to the `match` parameter
+/// of `pytest.raises()` where the string contains at least one unescaped
+/// regex metacharacter.
+///
+/// ## Why is this bad?
+/// The `match` argument is implicitly converted to a regex under the hood.
+/// It should be made explicit whether the string is meant to be a regex or a "plain" pattern
+/// by prefixing the string with the `r` suffix, escaping the metacharacter(s)
+/// in the string using backslashes, or wrapping the entire string in a call to
+/// `re.escape()`.
+///
+/// ## Example
+///
+/// ```python
+/// import pytest
+///
+///
+/// with pytest.raises(Exception, match="A full sentence."):
+///     do_thing_that_raises()
+/// ```
+///
+/// Use instead:
+///
+/// ```python
+/// import pytest
+///
+///
+/// with pytest.raises(Exception, match=r"A full sentence."):
+///     do_thing_that_raises()
+/// ```
+///
+/// Alternatively:
+///
+/// ```python
+/// import pytest
+/// import re
+///
+///
+/// with pytest.raises(Exception, match=re.escape("A full sentence.")):
+///     do_thing_that_raises()
+/// ```
+///
+/// or:
+///
+/// ```python
+/// import pytest
+/// import re
+///
+///
+/// with pytest.raises(Exception, "A full sentence\\."):
+///     do_thing_that_raises()
+/// ```
+///
+/// ## References
+/// - [Python documentation: `re.escape`](https://docs.python.org/3/library/re.html#re.escape)
+/// - [`pytest` documentation: `pytest.raises`](https://docs.pytest.org/en/latest/reference/reference.html#pytest-raises)
+#[derive(ViolationMetadata)]
+pub(crate) struct PytestRaisesAmbiguousPattern;
+
+impl Violation for PytestRaisesAmbiguousPattern {
+    #[derive_message_formats]
+    fn message(&self) -> String {
+        "Pattern passed to `match=` contains metacharacters but is neither escaped nor raw"
+            .to_string()
+    }
+
+    fn fix_title(&self) -> Option<String> {
+        Some("Use a raw string or `re.escape()` to make the intention explicit".to_string())
+    }
+}
+
+/// RUF043
+pub(crate) fn pytest_raises_ambiguous_pattern(checker: &mut Checker, call: &ast::ExprCall) {
+    if !is_pytest_raises(&call.func, checker.semantic()) {
+        return;
+    }
+
+    // It *can* be passed as a positional argument if you try very hard,
+    // but pytest only documents it as a keyword argument, and it's quite hard pass it positionally
+    let Some(ast::Keyword { value, .. }) = call.arguments.find_keyword("match") else {
+        return;
+    };
+
+    let ast::Expr::StringLiteral(string) = value else {
+        return;
+    };
+
+    let any_part_is_raw = string.value.iter().any(|part| part.flags.prefix().is_raw());
+
+    if any_part_is_raw || !string_has_unescaped_metacharacters(&string.value) {
+        return;
+    }
+
+    let diagnostic = Diagnostic::new(PytestRaisesAmbiguousPattern, string.range);
+
+    checker.diagnostics.push(diagnostic);
+}
+
+fn string_has_unescaped_metacharacters(value: &ast::StringLiteralValue) -> bool {
+    let mut escaped = false;
+
+    for character in value.chars() {
+        if escaped {
+            if escaped_char_is_regex_metasequence(character) {
+                return true;
+            }
+
+            escaped = false;
+            continue;
+        }
+
+        if character == '\\' {
+            escaped = true;
+            continue;
+        }
+
+        if char_is_regex_metacharacter(character) {
+            return true;
+        }
+    }
+
+    false
+}
+
+/// Whether the sequence `\<c>` means anything special:
+///
+/// * `\A`: Start of input
+/// * `\b`, `\B`: Word boundary and non-word-boundary
+/// * `\d`, `\D`: Digit and non-digit
+/// * `\s`, `\S`: Whitespace and non-whitespace
+/// * `\w`, `\W`: Word and non-word character
+/// * `\z`: End of input
+///
+/// `\u`, `\U`, `\N`, `\x`, `\a`, `\f`, `\n`, `\r`, `\t`, `\v`
+/// are also valid in normal strings and thus do not count.
+/// `\b` means backspace only in character sets,
+/// while backreferences (e.g., `\1`) are not valid without groups,
+/// both of which should be caught in [`string_has_unescaped_metacharacters`].
+const fn escaped_char_is_regex_metasequence(c: char) -> bool {
+    matches!(c, 'A' | 'b' | 'B' | 'd' | 'D' | 's' | 'S' | 'w' | 'W' | 'z')
+}
+
+const fn char_is_regex_metacharacter(c: char) -> bool {
+    matches!(
+        c,
+        '.' | '^' | '$' | '*' | '+' | '?' | '{' | '[' | '\\' | '|' | '('
+    )
+}