refactor(symfony-string): extract symfony/string into the shirabe-symfony-string crate

Move `Symfony\Component\String` out of shirabe-external-packages and into
its own crate, so the path is `shirabe_symfony_string::ByteString`
instead of `shirabe_external_packages::symfony::string::ByteString`.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

1 files changed, 45 insertions, 0 deletions

diff --git a/crates/shirabe-symfony-string/src/byte_string.rs b/crates/shirabe-symfony-string/src/byte_string.rs
new file mode 100644
index 00000000..cf597bbf
--- /dev/null
+++ b/crates/shirabe-symfony-string/src/byte_string.rs
@@ -0,0 +1,45 @@
+//! ref: composer/vendor/symfony/string/ByteString.php
+
+use crate::code_point_string::CodePointString;
+
+#[derive(Debug, Clone)]
+pub struct ByteString {
+    pub(crate) string: String,
+}
+
+impl ByteString {
+    pub fn new(string: &str) -> Self {
+        Self {
+            string: string.to_string(),
+        }
+    }
+
+    /// `from_encoding` is `""` for PHP's `null`.
+    pub fn to_code_point_string(&self, from_encoding: &str) -> CodePointString {
+        // The source `string` is always valid UTF-8 (Rust `String`/`&str` guarantee), so
+        // `preg_match('//u', ...)` always holds.
+        if matches!(from_encoding, "" | "utf8" | "utf-8" | "UTF8" | "UTF-8") {
+            return CodePointString {
+                string: self.string.clone(),
+            };
+        }
+
+        let valid_encoding = shirabe_php_shim::mb_detect_encoding(
+            &self.string,
+            Some(vec![from_encoding.to_string()]),
+            true,
+        )
+        .is_some();
+        // PHP throws InvalidArgumentException. Callers detect `from_encoding` from this very
+        // string, so a mismatch is a programming error.
+        assert!(valid_encoding, "Invalid \"{}\" string.", from_encoding);
+
+        CodePointString {
+            string: shirabe_php_shim::mb_convert_encoding(
+                self.string.clone().into_bytes(),
+                "UTF-8",
+                from_encoding,
+            ),
+        }
+    }
+}