Refactor shebang parsing to remove regex dependency (#5690)

## Summary

Similar to #5567, we can remove the use of regex, plus simplify the
representation (use `Option`), add snapshot tests, etc.

This is about 100x faster than using a regex for cases that match (2.5ns
vs. 250ns). It's obviously not a hot path, but I prefer the consistency
with other similar comment-parsing. I may DRY these up into some common
functionality later on.

crates/ruff/src/checkers/physical_lines.rs

@@ -9,7 +9,7 @@ use ruff_python_whitespace::UniversalNewlines;
 
 use crate::registry::Rule;
 use crate::rules::flake8_copyright::rules::missing_copyright_notice;
-use crate::rules::flake8_executable::helpers::{extract_shebang, ShebangDirective};
+use crate::rules::flake8_executable::helpers::ShebangDirective;
 use crate::rules::flake8_executable::rules::{
     shebang_missing, shebang_newline, shebang_not_executable, shebang_python, shebang_whitespace,
 };
@@ -87,33 +87,35 @@ pub(crate) fn check_physical_lines(
                 || enforce_shebang_newline
                 || enforce_shebang_python
             {
-                let shebang = extract_shebang(&line);
-                if enforce_shebang_not_executable {
-                    if let Some(diagnostic) = shebang_not_executable(path, line.range(), &shebang) {
-                        diagnostics.push(diagnostic);
+                if let Some(shebang) = ShebangDirective::try_extract(&line) {
+                    has_any_shebang = true;
+                    if enforce_shebang_not_executable {
+                        if let Some(diagnostic) =
+                            shebang_not_executable(path, line.range(), &shebang)
+                        {
+                            diagnostics.push(diagnostic);
+                        }
                     }
-                }
-                if enforce_shebang_missing {
-                    if !has_any_shebang && matches!(shebang, ShebangDirective::Match(..)) {
-                        has_any_shebang = true;
+                    if enforce_shebang_whitespace {
+                        if let Some(diagnostic) =
+                            shebang_whitespace(line.range(), &shebang, fix_shebang_whitespace)
+                        {
+                            diagnostics.push(diagnostic);
+                        }
                     }
-                }
-                if enforce_shebang_whitespace {
-                    if let Some(diagnostic) =
-                        shebang_whitespace(line.range(), &shebang, fix_shebang_whitespace)
-                    {
-                        diagnostics.push(diagnostic);
+                    if enforce_shebang_newline {
+                        if let Some(diagnostic) =
+                            shebang_newline(line.range(), &shebang, index == 0)
+                        {
+                            diagnostics.push(diagnostic);
+                        }
                     }
-                }
-                if enforce_shebang_newline {
-                    if let Some(diagnostic) = shebang_newline(line.range(), &shebang, index == 0) {
-                        diagnostics.push(diagnostic);
-                    }
-                }
-                if enforce_shebang_python {
-                    if let Some(diagnostic) = shebang_python(line.range(), &shebang) {
-                        diagnostics.push(diagnostic);
+                    if enforce_shebang_python {
+                        if let Some(diagnostic) = shebang_python(line.range(), &shebang) {
+                            diagnostics.push(diagnostic);
+                        }
                     }
+                } else {
                 }
             }
         }

crates/ruff/src/rules/flake8_executable/helpers.rs

@@ -5,84 +5,88 @@ use std::path::Path;
 
 #[cfg(target_family = "unix")]
 use anyhow::Result;
-use once_cell::sync::Lazy;
-use regex::Regex;
 use ruff_text_size::{TextLen, TextSize};
 
-static SHEBANG_REGEX: Lazy<Regex> =
-    Lazy::new(|| Regex::new(r"^(?P<spaces>\s*)#!(?P<directive>.*)").unwrap());
-
+/// A shebang directive (e.g., `#!/usr/bin/env python3`).
 #[derive(Debug, PartialEq, Eq)]
-pub(crate) enum ShebangDirective<'a> {
-    None,
-    // whitespace length, start of the shebang, contents
-    Match(TextSize, TextSize, &'a str),
+pub(crate) struct ShebangDirective<'a> {
+    /// The offset of the directive contents (e.g., `/usr/bin/env python3`) from the start of the
+    /// line.
+    pub(crate) offset: TextSize,
+    /// The contents of the directive (e.g., `"/usr/bin/env python3"`).
+    pub(crate) contents: &'a str,
 }
 
-pub(crate) fn extract_shebang(line: &str) -> ShebangDirective {
-    // Minor optimization to avoid matches in the common case.
-    if !line.contains('!') {
-        return ShebangDirective::None;
+impl<'a> ShebangDirective<'a> {
+    /// Parse a shebang directive from a line, or return `None` if the line does not contain a
+    /// shebang directive.
+    pub(crate) fn try_extract(line: &'a str) -> Option<Self> {
+        // Trim whitespace.
+        let directive = Self::lex_whitespace(line);
+
+        // Trim the `#!` prefix.
+        let directive = Self::lex_char(directive, '#')?;
+        let directive = Self::lex_char(directive, '!')?;
+
+        Some(Self {
+            offset: line.text_len() - directive.text_len(),
+            contents: directive,
+        })
     }
-    match SHEBANG_REGEX.captures(line) {
-        Some(caps) => match caps.name("spaces") {
-            Some(spaces) => match caps.name("directive") {
-                Some(matches) => ShebangDirective::Match(
-                    spaces.as_str().text_len(),
-                    TextSize::try_from(matches.start()).unwrap(),
-                    matches.as_str(),
-                ),
-                None => ShebangDirective::None,
-            },
-            None => ShebangDirective::None,
-        },
-        None => ShebangDirective::None,
+
+    /// Lex optional leading whitespace.
+    #[inline]
+    fn lex_whitespace(line: &str) -> &str {
+        line.trim_start()
+    }
+
+    /// Lex a specific character, or return `None` if the character is not the first character in
+    /// the line.
+    #[inline]
+    fn lex_char(line: &str, c: char) -> Option<&str> {
+        let mut chars = line.chars();
+        if chars.next() == Some(c) {
+            Some(chars.as_str())
+        } else {
+            None
+        }
     }
 }
 
 #[cfg(target_family = "unix")]
-pub(crate) fn is_executable(filepath: &Path) -> Result<bool> {
-    {
-        let metadata = filepath.metadata()?;
-        let permissions = metadata.permissions();
-        Ok(permissions.mode() & 0o111 != 0)
-    }
+pub(super) fn is_executable(filepath: &Path) -> Result<bool> {
+    let metadata = filepath.metadata()?;
+    let permissions = metadata.permissions();
+    Ok(permissions.mode() & 0o111 != 0)
 }
 
 #[cfg(test)]
 mod tests {
-    use ruff_text_size::TextSize;
+    use insta::assert_debug_snapshot;
+
+    use crate::rules::flake8_executable::helpers::ShebangDirective;
 
-    use crate::rules::flake8_executable::helpers::{
-        extract_shebang, ShebangDirective, SHEBANG_REGEX,
-    };
+    #[test]
+    fn shebang_non_match() {
+        let source = "not a match";
+        assert_debug_snapshot!(ShebangDirective::try_extract(source));
+    }
 
     #[test]
-    fn shebang_regex() {
-        // Positive cases
-        assert!(SHEBANG_REGEX.is_match("#!/usr/bin/python"));
-        assert!(SHEBANG_REGEX.is_match("#!/usr/bin/env python"));
-        assert!(SHEBANG_REGEX.is_match("    #!/usr/bin/env python"));
-        assert!(SHEBANG_REGEX.is_match("  #!/usr/bin/env python"));
+    fn shebang_end_of_line() {
+        let source = "print('test')  #!/usr/bin/python";
+        assert_debug_snapshot!(ShebangDirective::try_extract(source));
+    }
 
-        // Negative cases
-        assert!(!SHEBANG_REGEX.is_match("hello world"));
+    #[test]
+    fn shebang_match() {
+        let source = "#!/usr/bin/env python";
+        assert_debug_snapshot!(ShebangDirective::try_extract(source));
     }
 
     #[test]
-    fn shebang_extract_match() {
-        assert_eq!(extract_shebang("not a match"), ShebangDirective::None);
-        assert_eq!(
-            extract_shebang("#!/usr/bin/env python"),
-            ShebangDirective::Match(TextSize::from(0), TextSize::from(2), "/usr/bin/env python")
-        );
-        assert_eq!(
-            extract_shebang("  #!/usr/bin/env python"),
-            ShebangDirective::Match(TextSize::from(2), TextSize::from(4), "/usr/bin/env python")
-        );
-        assert_eq!(
-            extract_shebang("print('test')  #!/usr/bin/python"),
-            ShebangDirective::None
-        );
+    fn shebang_leading_space() {
+        let source = "  #!/usr/bin/env python";
+        assert_debug_snapshot!(ShebangDirective::try_extract(source));
     }
 }

crates/ruff/src/rules/flake8_executable/rules/shebang_newline.rs

@@ -47,17 +47,14 @@ pub(crate) fn shebang_newline(
     shebang: &ShebangDirective,
     first_line: bool,
 ) -> Option<Diagnostic> {
-    if let ShebangDirective::Match(_, start, content) = shebang {
-        if first_line {
-            None
-        } else {
-            let diagnostic = Diagnostic::new(
-                ShebangNotFirstLine,
-                TextRange::at(range.start() + start, content.text_len()),
-            );
-            Some(diagnostic)
-        }
-    } else {
+    let ShebangDirective { offset, contents } = shebang;
+
+    if first_line {
         None
+    } else {
+        Some(Diagnostic::new(
+            ShebangNotFirstLine,
+            TextRange::at(range.start() + offset, contents.text_len()),
+        ))
     }
 }

crates/ruff/src/rules/flake8_executable/rules/shebang_not_executable.rs

@@ -48,15 +48,16 @@ pub(crate) fn shebang_not_executable(
     range: TextRange,
     shebang: &ShebangDirective,
 ) -> Option<Diagnostic> {
-    if let ShebangDirective::Match(_, start, content) = shebang {
-        if let Ok(false) = is_executable(filepath) {
-            let diagnostic = Diagnostic::new(
-                ShebangNotExecutable,
-                TextRange::at(range.start() + start, content.text_len()),
-            );
-            return Some(diagnostic);
-        }
+    let ShebangDirective { offset, contents } = shebang;
+
+    if let Ok(false) = is_executable(filepath) {
+        let diagnostic = Diagnostic::new(
+            ShebangNotExecutable,
+            TextRange::at(range.start() + offset, contents.text_len()),
+        );
+        return Some(diagnostic);
     }
+
     None
 }
 

crates/ruff/src/rules/flake8_executable/rules/shebang_python.rs

@@ -42,19 +42,14 @@ impl Violation for ShebangMissingPython {
 
 /// EXE003
 pub(crate) fn shebang_python(range: TextRange, shebang: &ShebangDirective) -> Option<Diagnostic> {
-    if let ShebangDirective::Match(_, start, content) = shebang {
-        if content.contains("python") || content.contains("pytest") {
-            None
-        } else {
-            let diagnostic = Diagnostic::new(
-                ShebangMissingPython,
-                TextRange::at(range.start() + start, content.text_len())
-                    .sub_start(TextSize::from(2)),
-            );
+    let ShebangDirective { offset, contents } = shebang;
 
-            Some(diagnostic)
-        }
-    } else {
+    if contents.contains("python") || contents.contains("pytest") {
         None
+    } else {
+        Some(Diagnostic::new(
+            ShebangMissingPython,
+            TextRange::at(range.start() + offset, contents.text_len()).sub_start(TextSize::from(2)),
+        ))
     }
 }

crates/ruff/src/rules/flake8_executable/rules/shebang_whitespace.rs

@@ -1,4 +1,5 @@
 use ruff_text_size::{TextRange, TextSize};
+use std::ops::Sub;
 
 use ruff_diagnostics::{AlwaysAutofixableViolation, Diagnostic, Edit, Fix};
 use ruff_macros::{derive_message_formats, violation};
@@ -49,22 +50,25 @@ pub(crate) fn shebang_whitespace(
     shebang: &ShebangDirective,
     autofix: bool,
 ) -> Option<Diagnostic> {
-    if let ShebangDirective::Match(n_spaces, start, ..) = shebang {
-        if *n_spaces > TextSize::from(0) && *start == n_spaces + TextSize::from(2) {
-            let mut diagnostic = Diagnostic::new(
-                ShebangLeadingWhitespace,
-                TextRange::at(range.start(), *n_spaces),
-            );
-            if autofix {
-                diagnostic.set_fix(Fix::automatic(Edit::range_deletion(TextRange::at(
-                    range.start(),
-                    *n_spaces,
-                ))));
-            }
-            Some(diagnostic)
-        } else {
-            None
+    let ShebangDirective {
+        offset,
+        contents: _,
+    } = shebang;
+
+    if *offset > TextSize::from(2) {
+        let leading_space_start = range.start();
+        let leading_space_len = offset.sub(TextSize::new(2));
+        let mut diagnostic = Diagnostic::new(
+            ShebangLeadingWhitespace,
+            TextRange::at(leading_space_start, leading_space_len),
+        );
+        if autofix {
+            diagnostic.set_fix(Fix::automatic(Edit::range_deletion(TextRange::at(
+                leading_space_start,
+                leading_space_len,
+            ))));
         }
+        Some(diagnostic)
     } else {
         None
     }

crates/ruff/src/rules/flake8_executable/snapshots/ruff__rules__flake8_executable__helpers__tests__shebang_end_of_line.snap

@@ -0,0 +1,5 @@
+---
+source: crates/ruff/src/rules/flake8_executable/helpers.rs
+expression: "ShebangDirective::try_extract(source)"
+---
+None

crates/ruff/src/rules/flake8_executable/snapshots/ruff__rules__flake8_executable__helpers__tests__shebang_leading_space.snap

@@ -0,0 +1,10 @@
+---
+source: crates/ruff/src/rules/flake8_executable/helpers.rs
+expression: "ShebangDirective::try_extract(source)"
+---
+Some(
+    ShebangDirective {
+        offset: 4,
+        contents: "/usr/bin/env python",
+    },
+)

crates/ruff/src/rules/flake8_executable/snapshots/ruff__rules__flake8_executable__helpers__tests__shebang_match.snap

@@ -0,0 +1,10 @@
+---
+source: crates/ruff/src/rules/flake8_executable/helpers.rs
+expression: "ShebangDirective::try_extract(source)"
+---
+Some(
+    ShebangDirective {
+        offset: 2,
+        contents: "/usr/bin/env python",
+    },
+)

crates/ruff/src/rules/flake8_executable/snapshots/ruff__rules__flake8_executable__helpers__tests__shebang_non_match.snap

@@ -0,0 +1,5 @@
+---
+source: crates/ruff/src/rules/flake8_executable/helpers.rs
+expression: "ShebangDirective::try_extract(source)"
+---
+None