improve the env fuzzer

fuzz/fuzz_targets/fuzz_env.rs

@@ -17,22 +17,36 @@
 
 static CMD_PATH: &str = "env";
 
+/// A non-empty variable name. `env "=value"` is a known divergence: GNU injects
+/// the empty name into environ via putenv(), we reject it on purpose.
+fn generate_env_name() -> String {
+    let mut rng = rand::rng();
+    loop {
+        let name = generate_random_string(rng.random_range(1..10));
+        if !name.is_empty() {
+            return name;
+        }
+    }
+}
+
 fn generate_env_args() -> Vec<String> {
     let mut rng = rand::rng();
-    let mut args = Vec::new();
 
-    let opts = ["-i", "-0", "-v", "-vv"];
-    for opt in &opts {
-        if rng.random_bool(0.2) {
-            args.push(opt.to_string());
-        }
+    // -i is mandatory: we run uumain in-process, so without it the Rust side
+    // sees the fuzzer's environment plus set_var leftovers from earlier
+    // iterations, while GNU runs as a child.
+    let mut args = vec![String::from("-i")];
+
+    if rng.random_bool(0.2) {
+        args.push(String::from("-0"));
     }
 
+    // -v/-vv skipped: we don't print GNU's "cleaning environ"/"setenv:"/"unset:".
+    // https://github.com/uutils/coreutils/issues/14171
+
     if rng.random_bool(0.3) {
-        args.push(format!(
-            "-u={}",
-            generate_random_string(rng.random_range(3..10))
-        ));
+        args.push(String::from("-u"));
+        args.push(generate_env_name());
     }
 
     if rng.random_bool(0.2) {
@@ -55,7 +69,7 @@
     for _ in 0..rng.random_range(0..3) {
         args.push(format!(
             "{}={}",
-            generate_random_string(5),
+            generate_env_name(),
             generate_random_string(5)
         ));
     }

tests/by-util/test_env.rs

@@ -375,6 +375,31 @@ fn test_empty_name() {
         .stderr_only("env: warning: no name specified for value 'xyz'\n");
 }
 
+// An empty name is dropped with a warning (GNU injects it via putenv, we
+// can't with set_var); the other assignments must still go through.
+#[test]
+fn test_empty_name_does_not_affect_other_assignments() {
+    let result = new_ucmd!()
+        .args(&["-i", "MOTOR=idle", "=zap", "GEARBOX=locked"])
+        .succeeds();
+    result.stderr_is("env: warning: no name specified for value 'zap'\n");
+
+    // Windows sorts the environment block, so don't depend on the order.
+    let mut vars: Vec<_> = result.stdout_str().lines().collect();
+    vars.sort_unstable();
+    assert_eq!(vars, ["GEARBOX=locked", "MOTOR=idle"]);
+}
+
+// "=" alone is name and value both empty; still just a warning, exit 0.
+#[test]
+fn test_empty_name_and_empty_value() {
+    new_ucmd!()
+        .args(&["-i", "="])
+        .succeeds()
+        .no_stdout()
+        .stderr_is("env: warning: no name specified for value ''\n");
+}
+
 #[test]
 fn test_null_delimiter() {
     let out = new_ucmd!()