feat(unstable): `--unstable-detect-cjs` for respecting explicit `"type": "commonjs"` (#26149)

When using the `--unstable-detect-cjs` flag or adding `"unstable":
["detect-cjs"]` to a deno.json, it will make a JS file CJS if the
closest package.json contains `"type": "commonjs"` and the file is not
an ESM module (no TLA, no `import.meta`, no `import`/`export`).

1 files changed, 18 insertions, 0 deletions

diff --git a/cli/util/text_encoding.rs b/cli/util/text_encoding.rs
index d2e0832c9..0b7601cb9 100644
--- a/cli/util/text_encoding.rs
+++ b/cli/util/text_encoding.rs
@@ -1,6 +1,8 @@
 // Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.
 
+use std::borrow::Cow;
 use std::ops::Range;
+use std::sync::Arc;
 
 use base64::prelude::BASE64_STANDARD;
 use base64::Engine;
@@ -9,6 +11,15 @@ use deno_core::ModuleSourceCode;
 static SOURCE_MAP_PREFIX: &[u8] =
   b"//# sourceMappingURL=data:application/json;base64,";
 
+pub fn from_utf8_lossy_owned(bytes: Vec<u8>) -> String {
+  match String::from_utf8_lossy(&bytes) {
+    Cow::Owned(code) => code,
+    // SAFETY: `String::from_utf8_lossy` guarantees that the result is valid
+    // UTF-8 if `Cow::Borrowed` is returned.
+    Cow::Borrowed(_) => unsafe { String::from_utf8_unchecked(bytes) },
+  }
+}
+
 pub fn source_map_from_code(code: &[u8]) -> Option<Vec<u8>> {
   let range = find_source_map_range(code)?;
   let source_map_range = &code[range];
@@ -85,6 +96,13 @@ fn find_source_map_range(code: &[u8]) -> Option<Range<usize>> {
   }
 }
 
+/// Converts an `Arc<str>` to an `Arc<[u8]>`.
+pub fn arc_str_to_bytes(arc_str: Arc<str>) -> Arc<[u8]> {
+  let raw = Arc::into_raw(arc_str);
+  // SAFETY: This is safe because they have the same memory layout.
+  unsafe { Arc::from_raw(raw as *const [u8]) }
+}
+
 #[cfg(test)]
 mod tests {
   use std::sync::Arc;