Rollup merge of #141840 - ChrisDenton:noempty, r=ChrisDenton

If `HOME` is empty, use the fallback instead

This is a minor change in the `home_dir` api. An empty path is never (or should never be) valid so if the `HOME` environment variable is empty then let's use the fallback instead.

r? libs-api

Author: jhpratt

library/std/src/env.rs

@@ -617,7 +617,7 @@ impl Error for JoinPathsError {
 /// # Unix
 ///
 /// - Returns the value of the 'HOME' environment variable if it is set
-///   (including to an empty string).
+///   (and not an empty string).
 /// - Otherwise, it tries to determine the home directory by invoking the `getpwuid_r` function
 ///   using the UID of the current user. An empty home directory field returned from the
 ///   `getpwuid_r` function is considered to be a valid value.

library/std/src/sys/pal/unix/os.rs

@@ -633,7 +633,10 @@ pub fn temp_dir() -> PathBuf {
 }
 
 pub fn home_dir() -> Option<PathBuf> {
-    return crate::env::var_os("HOME").or_else(|| unsafe { fallback() }).map(PathBuf::from);
+    return crate::env::var_os("HOME")
+        .filter(|s| !s.is_empty())
+        .or_else(|| unsafe { fallback() })
+        .map(PathBuf::from);
 
     #[cfg(any(
         target_os = "android",