From d99d8441523578e2d4b0e61196ce82fa15fd72b0 Mon Sep 17 00:00:00 2001
From: Ed Morley <emorley@salesforce.com>
Date: Fri, 2 Oct 2026 14:16:30 +0100
Subject: [PATCH] Enable `flate2`'s `runtime_detection` feature

As of `flate2` 1.1.10, runtime CPU feature detection (and so SIMD
acceleration) in `zlib-rs` is gated behind the new `runtime_detection`
default feature, which is disabled by our use of
`default-features = false`, so has to be enabled explicitly. The
`flate2` docs don't currently mention this, see:
https://github.com/rust-lang/flate2-rs/issues/570

GUS-W-24154015.
---
 CHANGELOG.md |  4 ++++
 Cargo.lock   | 10 ++++++++++
 Cargo.toml   |  2 +-
 3 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index b5ec7a7..74f2fbd 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,6 +11,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Updated libcnb to 0.32.0, which includes OpenTelemetry crate upgrades. ([#629](https://github.com/heroku/buildpacks-python/pull/629))
 
+### Fixed
+
+- Restored SIMD-accelerated decompression of the uv download. ([#628](https://github.com/heroku/buildpacks-python/pull/628))
+
 ## [6.7.0] - 2026-10-02
 
 ### Changed
diff --git a/Cargo.lock b/Cargo.lock
index 535eeaa..12406d9 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -144,6 +144,15 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "crc32fast"
+version = "1.5.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "01a7799fd6b852db0e61728dde9a204c423b44d689dbd432522543614b490e78"
+dependencies = [
+ "cfg-if",
+]
+
 [[package]]
 name = "crossbeam-deque"
 version = "0.8.8"
@@ -247,6 +256,7 @@ version = "1.1.10"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "6e634e2e0ebac1ee034020da1ca582e17ffe4e0f5e985823721e168928136dcb"
 dependencies = [
+ "crc32fast",
  "zlib-rs",
 ]
 
diff --git a/Cargo.toml b/Cargo.toml
index a0f594a..b9cae74 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -24,7 +24,7 @@ result_large_err = "allow"
 # We use the `zlib-rs` backend, since it's the fastest:
 # https://github.com/rust-lang/flate2-rs#backends
 # https://trifectatech.org/blog/zlib-rs-is-faster-than-c/
-flate2 = { version = "1", default-features = false, features = ["zlib-rs"] }
+flate2 = { version = "1", default-features = false, features = ["zlib-rs", "runtime_detection"] }
 indoc = "2"
 libcnb = { version = "=0.32.0", features = ["trace"] }
 libherokubuildpack = { version = "=0.32.0", default-features = false, features = ["log"] }