Allow symlinks to files in scripts directory (#5380)

## Summary

Closes https://github.com/astral-sh/uv/issues/5359.

## Test Plan

Unfortunately, the only packages I know of that use this are Ruff and
uv, and both are too heavy to install in a recurring test, so:

`uv tool install hatch==1.12.0 --with uv==0.2.27 --force
--link-mode=symlink`

crates/install-wheel-rs/src/wheel.rs

@@ -441,13 +441,31 @@ fn install_script(
     record: &mut [RecordEntry],
     file: &DirEntry,
 ) -> Result<(), Error> {
-    if !file.file_type()?.is_file() {
+    let file_type = file.file_type()?;
+
+    if file_type.is_dir() {
         return Err(Error::InvalidWheel(format!(
-            "Wheel contains entry in scripts directory that is not a file: {}",
-            file.path().display()
+            "Wheel contains an invalid entry (directory) in the `scripts` directory: {}",
+            file.path().simplified_display()
         )));
     }
 
+    if file_type.is_symlink() {
+        let Ok(target) = file.path().canonicalize() else {
+            return Err(Error::InvalidWheel(format!(
+                "Wheel contains an invalid entry (broken symlink) in the `scripts` directory: {}",
+                file.path().simplified_display(),
+            )));
+        };
+        if target.is_dir() {
+            return Err(Error::InvalidWheel(format!(
+                "Wheel contains an invalid entry (directory symlink) in the `scripts` directory: {} ({})",
+                file.path().simplified_display(),
+                target.simplified_display()
+            )));
+        }
+    }
+
     let script_absolute = layout.scheme.scripts.join(file.file_name());
     let script_relative =
         pathdiff::diff_paths(&script_absolute, site_packages).ok_or_else(|| {

crates/uv/tests/pip_sync.rs

@@ -105,12 +105,16 @@ fn install() -> Result<()> {
         .join("__init__.cpython-312.pyc")
         .exists());
 
-    context.assert_command("import markupsafe").success();
+    context
+        .assert_command("from markupsafe import Markup")
+        .success();
 
     // Removing the cache shouldn't invalidate the virtual environment.
     fs::remove_dir_all(context.cache_dir.path())?;
 
-    context.assert_command("import markupsafe").success();
+    context
+        .assert_command("from markupsafe import Markup")
+        .success();
 
     Ok(())
 }
@@ -140,12 +144,16 @@ fn install_copy() -> Result<()> {
     "###
     );
 
-    context.assert_command("import markupsafe").success();
+    context
+        .assert_command("from markupsafe import Markup")
+        .success();
 
     // Removing the cache shouldn't invalidate the virtual environment.
     fs::remove_dir_all(context.cache_dir.path())?;
 
-    context.assert_command("import markupsafe").success();
+    context
+        .assert_command("from markupsafe import Markup")
+        .success();
 
     Ok(())
 }
@@ -175,12 +183,55 @@ fn install_hardlink() -> Result<()> {
     "###
     );
 
-    context.assert_command("import markupsafe").success();
+    context
+        .assert_command("from markupsafe import Markup")
+        .success();
 
     // Removing the cache shouldn't invalidate the virtual environment.
     fs::remove_dir_all(context.cache_dir.path())?;
 
-    context.assert_command("import markupsafe").success();
+    context
+        .assert_command("from markupsafe import Markup")
+        .success();
+
+    Ok(())
+}
+
+/// Install a package into a virtual environment using symlink semantics.
+#[test]
+fn install_symlink() -> Result<()> {
+    let context = TestContext::new("3.12");
+
+    let requirements_txt = context.temp_dir.child("requirements.txt");
+    requirements_txt.write_str("MarkupSafe==2.1.3")?;
+
+    uv_snapshot!(context.pip_sync()
+        .arg("requirements.txt")
+        .arg("--link-mode")
+        .arg("symlink")
+        .arg("--strict"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 1 package in [TIME]
+    Prepared 1 package in [TIME]
+    Installed 1 package in [TIME]
+     + markupsafe==2.1.3
+    "###
+    );
+
+    context
+        .assert_command("from markupsafe import Markup")
+        .success();
+
+    // Removing the cache _should_ invalidate the virtual environment.
+    fs::remove_dir_all(context.cache_dir.path())?;
+
+    context
+        .assert_command("from markupsafe import Markup")
+        .failure();
 
     Ok(())
 }
@@ -210,7 +261,7 @@ fn install_many() -> Result<()> {
     );
 
     context
-        .assert_command("import markupsafe; import tomli")
+        .assert_command("from markupsafe import Markup; import tomli")
         .success();
 
     Ok(())
@@ -244,7 +295,9 @@ fn noop() -> Result<()> {
     "###
     );
 
-    context.assert_command("import markupsafe").success();
+    context
+        .assert_command("from markupsafe import Markup")
+        .success();
 
     Ok(())
 }