Rename ruff_python crate to ruff_python_stdlib (#3354)

In hindsight, `ruff_python` is too general. A good giveaway is that it's actually a prefix of some other crates. The intent of this crate is to reimplement pieces of the Python standard library and CPython itself, so `ruff_python_stdlib` feels appropriate.

crates/ruff_python_stdlib/src/str.rs

@@ -0,0 +1,87 @@
+use once_cell::sync::Lazy;
+use regex::Regex;
+
+/// See: <https://docs.python.org/3/reference/lexical_analysis.html#string-and-bytes-literals>
+pub const TRIPLE_QUOTE_PREFIXES: &[&str] = &[
+    "u\"\"\"", "u'''", "r\"\"\"", "r'''", "U\"\"\"", "U'''", "R\"\"\"", "R'''", "\"\"\"", "'''",
+];
+pub const SINGLE_QUOTE_PREFIXES: &[&str] = &[
+    "u\"", "u'", "r\"", "r'", "U\"", "U'", "R\"", "R'", "\"", "'",
+];
+pub const TRIPLE_QUOTE_SUFFIXES: &[&str] = &["\"\"\"", "'''"];
+pub const SINGLE_QUOTE_SUFFIXES: &[&str] = &["\"", "'"];
+
+pub static STRING_QUOTE_PREFIX_REGEX: Lazy<Regex> =
+    Lazy::new(|| Regex::new(r#"^(?i)[urb]*['"](?P<raw>.*)['"]$"#).unwrap());
+
+pub fn is_lower(s: &str) -> bool {
+    let mut cased = false;
+    for c in s.chars() {
+        if c.is_uppercase() {
+            return false;
+        } else if !cased && c.is_lowercase() {
+            cased = true;
+        }
+    }
+    cased
+}
+
+pub fn is_upper(s: &str) -> bool {
+    let mut cased = false;
+    for c in s.chars() {
+        if c.is_lowercase() {
+            return false;
+        } else if !cased && c.is_uppercase() {
+            cased = true;
+        }
+    }
+    cased
+}
+
+/// Remove prefixes (u, r, b) and quotes around a string. This expects the given
+/// string to be a valid Python string representation, it doesn't do any
+/// validation.
+pub fn strip_quotes_and_prefixes(s: &str) -> &str {
+    match STRING_QUOTE_PREFIX_REGEX.captures(s) {
+        Some(caps) => match caps.name("raw") {
+            Some(m) => m.as_str(),
+            None => s,
+        },
+        None => s,
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::str::{is_lower, is_upper, strip_quotes_and_prefixes};
+
+    #[test]
+    fn test_is_lower() {
+        assert!(is_lower("abc"));
+        assert!(is_lower("a_b_c"));
+        assert!(is_lower("a2c"));
+        assert!(!is_lower("aBc"));
+        assert!(!is_lower("ABC"));
+        assert!(!is_lower(""));
+        assert!(!is_lower("_"));
+    }
+
+    #[test]
+    fn test_is_upper() {
+        assert!(is_upper("ABC"));
+        assert!(is_upper("A_B_C"));
+        assert!(is_upper("A2C"));
+        assert!(!is_upper("aBc"));
+        assert!(!is_upper("abc"));
+        assert!(!is_upper(""));
+        assert!(!is_upper("_"));
+    }
+
+    #[test]
+    fn test_strip_quotes_and_prefixes() {
+        assert_eq!(strip_quotes_and_prefixes(r#"'a'"#), "a");
+        assert_eq!(strip_quotes_and_prefixes(r#"bur'a'"#), "a");
+        assert_eq!(strip_quotes_and_prefixes(r#"UrB'a'"#), "a");
+        assert_eq!(strip_quotes_and_prefixes(r#""a""#), "a");
+    }
+}