Discard forks when using `--upgrade` (#5905)

Fixes #5817

Needs https://github.com/astral-sh/packse/pull/213 for the test to pass.

crates/uv/src/commands/project/lock.rs

@@ -420,8 +420,12 @@ async fn do_lock(
     // "preferences-dependent-forking" packse scenario). To avoid this, we store the forks in the
     // lockfile. We read those after all the lockfile filters, to allow the forks to change when
     // the environment changed, e.g. the python bound check above can lead to different forking.
-    let resolver_markers =
+    let resolver_markers = ResolverMarkers::universal(if upgrade.is_all() {
-        ResolverMarkers::universal(existing_lock.and_then(|lock| lock.fork_markers().clone()));
+        // We're discarding all preferences, so we're also discarding the existing forks.
+        None
+    } else {
+        existing_lock.and_then(|lock| lock.fork_markers().clone())
+    });
 
     let resolution = match existing_lock.filter(|_| upgrade.is_none()) {
         None => None,

crates/uv/tests/lock.rs

@@ -1,11 +1,13 @@
 #![cfg(all(feature = "python", feature = "pypi"))]
 
 use anyhow::Result;
+use assert_cmd::assert::OutputAssertExt;
 use assert_fs::prelude::*;
 use indoc::{formatdoc, indoc};
 use insta::assert_snapshot;
 use url::Url;
 
+use crate::common::packse_index_url;
 use common::{uv_snapshot, TestContext};
 
 mod common;
@@ -2208,10 +2210,6 @@ fn lock_upgrade_log_multi_version() -> Result<()> {
             lock, @r###"
         version = 1
         requires-python = ">=3.12"
-        environment-markers = [
-            "sys_platform == 'win32'",
-            "sys_platform != 'win32'",
-        ]
 
         [options]
         exclude-newer = "2024-03-25 00:00:00 UTC"
@@ -5804,3 +5802,42 @@ fn lock_upgrade_package() -> Result<()> {
 
     Ok(())
 }
+
+/// Check that we discard the fork marker from the lockfile when using `--upgrade`.
+#[test]
+fn lock_upgrade_drop_fork_markers() -> Result<()> {
+    let context = TestContext::new("3.12");
+
+    let requirements = r#"[project]
+    name = "forking"
+    version = "0.1.0"
+    requires-python = ">=3.12"
+    dependencies = ["fork-upgrade-foo==1"]
+    "#;
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(requirements)?;
+    context
+        .lock()
+        .arg("--index-url")
+        .arg(packse_index_url())
+        .env_remove("UV_EXCLUDE_NEWER")
+        .assert()
+        .success();
+    let lock = fs_err::read_to_string(context.temp_dir.join("uv.lock")).unwrap();
+    assert!(lock.contains("environment-markers"));
+
+    // Remove the bound and lock with `--upgrade`.
+    pyproject_toml.write_str(&requirements.replace("fork-upgrade-foo==1", "fork-upgrade-foo"))?;
+    context
+        .lock()
+        .arg("--index-url")
+        .arg(packse_index_url())
+        .env_remove("UV_EXCLUDE_NEWER")
+        .arg("--upgrade")
+        .assert()
+        .success();
+    let lock = fs_err::read_to_string(context.temp_dir.join("uv.lock")).unwrap();
+    assert!(!lock.contains("environment-markers"));
+    Ok(())
+}