test(interpreter): add regression tests for issue #875 (#895)

Add tests verifying associative array key expansion (${!assoc[@]}) works correctly inside process substitution nested in command substitution. The bug was already fixed by prior commits but lacked a targeted regression test.

Closes #875

Author: chaliy

crates/bashkit/tests/issue_875_test.rs

@@ -0,0 +1,86 @@
+//! Test for issue #875: Associative array key expansion (`${!assoc[@]}`)
+//! returns empty when used inside a process substitution nested inside a
+//! command substitution.
+
+use bashkit::Bash;
+
+#[tokio::test]
+async fn assoc_keys_visible_in_nested_procsub_cmdsub() {
+    let mut bash = Bash::new();
+    let result = bash
+        .exec(
+            r#"
+myfunc() {
+  declare -A m=()
+  m["a"]="1"
+  m["b"]="2"
+
+  # Process substitution inside command substitution
+  result="$(while IFS= read -r k; do echo "$k"; done < <(printf '%s\n' "${!m[@]}"))"
+  echo "nested result: [$result]"
+}
+myfunc
+"#,
+        )
+        .await
+        .unwrap();
+    // Keys should be visible (order may vary since assoc arrays are unordered)
+    assert!(
+        result.stdout.contains("a") && result.stdout.contains("b"),
+        "expected keys 'a' and 'b' in nested result, got: {}",
+        result.stdout
+    );
+    assert!(
+        !result.stdout.contains("nested result: []"),
+        "nested result should not be empty, got: {}",
+        result.stdout
+    );
+}
+
+#[tokio::test]
+async fn assoc_keys_direct_expansion() {
+    let mut bash = Bash::new();
+    let result = bash
+        .exec(
+            r#"
+myfunc() {
+  declare -A m=()
+  m["x"]="10"
+  m["y"]="20"
+  echo "direct keys: ${!m[@]}"
+}
+myfunc
+"#,
+        )
+        .await
+        .unwrap();
+    assert!(
+        result.stdout.contains("x") && result.stdout.contains("y"),
+        "expected keys 'x' and 'y', got: {}",
+        result.stdout
+    );
+}
+
+#[tokio::test]
+async fn assoc_keys_in_procsub_alone() {
+    let mut bash = Bash::new();
+    let result = bash
+        .exec(
+            r#"
+myfunc() {
+  declare -A m=()
+  m["p"]="1"
+  m["q"]="2"
+  while IFS= read -r k; do echo "procsub: $k"; done < <(printf '%s\n' "${!m[@]}")
+}
+myfunc
+"#,
+        )
+        .await
+        .unwrap();
+    assert!(
+        result.stdout.contains("procsub: p") || result.stdout.contains("procsub: q"),
+        "expected keys in procsub output, got: {}",
+        result.stdout
+    );
+}