Improve affected stdin auto detection

Author: DominicVonk

crates/app/Cargo.toml

@@ -100,5 +100,8 @@ tiny_http = "0.12.0"
 serial_test = { workspace = true }
 starbase_sandbox = { workspace = true }
 
+[target.'cfg(unix)'.dependencies]
+nix = { version = "0.31.3", features = ["poll"] }
+
 [lints]
 workspace = true

crates/app/src/queries/changed_files.rs

@@ -4,13 +4,20 @@ use moon_common::is_ci;
 use moon_common::path::{WorkspaceRelativePathBuf, standardize_separators};
 use moon_env_var::GlobalEnvBag;
 use moon_vcs::{BoxedVcs, ChangedFiles, ChangedStatus};
+#[cfg(unix)]
+use nix::poll::{PollFd, PollFlags, PollTimeout, poll};
 use rustc_hash::FxHashSet;
 use serde::{Deserialize, Serialize};
 use starbase_styles::color;
 use starbase_utils::json;
+#[cfg(unix)]
+use std::os::fd::AsFd;
 use std::io::{IsTerminal, Read, stdin};
 use tracing::{debug, warn};
 
+#[cfg(unix)]
+const STDIN_READY_TIMEOUT_MS: u8 = 100;
+
 #[derive(Clone, Debug, Default, Deserialize, Serialize)]
 #[serde(rename_all = "camelCase")]
 pub struct QueryChangedFilesOptions {
@@ -225,7 +232,7 @@ pub async fn query_changed_files_for_affected(
     let mut options = QueryChangedFilesOptions {
         default_branch: ci,
         local: !ci,
-        stdin: true,
+        stdin: should_read_from_stdin()?,
         ..Default::default()
     };
 
@@ -237,3 +244,35 @@ pub async fn query_changed_files_for_affected(
         .await
         .map(|result| result.files)
 }
+
+fn should_read_from_stdin() -> miette::Result<bool> {
+    if stdin().is_terminal() {
+        return Ok(false);
+    }
+
+    // Non-TTY stdin can be an open CI handle with no data, so only read when ready.
+    is_stdin_readable()
+}
+
+#[cfg(unix)]
+fn is_stdin_readable() -> miette::Result<bool> {
+    let stdin = stdin();
+    let mut poll_fds = [PollFd::new(stdin.as_fd(), PollFlags::POLLIN)];
+    let ready = poll(
+        &mut poll_fds,
+        PollTimeout::from(STDIN_READY_TIMEOUT_MS),
+    )
+    .into_diagnostic()?;
+
+    let readable_events = PollFlags::POLLIN | PollFlags::POLLHUP | PollFlags::POLLERR;
+
+    Ok(ready > 0
+        && poll_fds[0]
+            .revents()
+            .is_some_and(|events| events.intersects(readable_events)))
+}
+
+#[cfg(not(unix))]
+fn is_stdin_readable() -> miette::Result<bool> {
+    Ok(true)
+}

crates/cli/tests/query_affected_test.rs

@@ -46,6 +46,29 @@ mod query_affected {
         );
     }
 
+    #[test]
+    fn includes_project_via_stdin() {
+        let sandbox = create_query_sandbox();
+
+        let assert = sandbox.run_bin(|cmd| {
+            cmd.arg("query")
+                .arg("affected")
+                .write_stdin("basic/file.txt");
+        });
+
+        let mut affected: Affected = serde_json::from_str(assert.stdout().trim()).unwrap();
+
+        assert!(!affected.projects.contains_key("advanced"));
+        assert_eq!(
+            affected.projects.remove("basic").unwrap(),
+            AffectedProjectState {
+                files: FxHashSet::from_iter(["basic/file.txt".into()]),
+                tasks: FxHashSet::from_iter([Target::parse("basic:dev").unwrap()]),
+                ..Default::default()
+            }
+        );
+    }
+
     #[test]
     fn includes_task_for_input() {
         let sandbox = create_query_sandbox();