zombie_processes: do not complain about early early returns (#14912)

If an early return is found under the HIR local declaration node but
before the child process is created, it should not trigger the lint
because the child process has not yet been created.

changelog: [`zombie_process`]: do not complain about early early returns

Fixes rust-lang/rust-clippy#14911

Author: Jarcho

clippy_lints/src/zombie_processes.rs

@@ -5,7 +5,7 @@ use rustc_ast::Mutability;
 use rustc_ast::visit::visit_opt;
 use rustc_errors::Applicability;
 use rustc_hir::def_id::LocalDefId;
-use rustc_hir::intravisit::{Visitor, walk_block, walk_expr, walk_local};
+use rustc_hir::intravisit::{Visitor, walk_block, walk_expr};
 use rustc_hir::{Expr, ExprKind, HirId, LetStmt, Node, PatKind, Stmt, StmtKind};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::hir::nested_filter;
@@ -69,8 +69,9 @@ impl<'tcx> LateLintPass<'tcx> for ZombieProcesses {
                     let mut vis = WaitFinder {
                         cx,
                         local_id,
+                        create_id: expr.hir_id,
                         body_id: cx.tcx.hir_enclosing_body_owner(expr.hir_id),
-                        state: VisitorState::WalkUpToLocal,
+                        state: VisitorState::WalkUpToCreate,
                         early_return: None,
                         missing_wait_branch: None,
                     };
@@ -131,6 +132,7 @@ struct MaybeWait(Span);
 struct WaitFinder<'a, 'tcx> {
     cx: &'a LateContext<'tcx>,
     local_id: HirId,
+    create_id: HirId,
     body_id: LocalDefId,
     state: VisitorState,
     early_return: Option<Span>,
@@ -141,8 +143,8 @@ struct WaitFinder<'a, 'tcx> {
 
 #[derive(PartialEq)]
 enum VisitorState {
-    WalkUpToLocal,
-    LocalFound,
+    WalkUpToCreate,
+    CreateFound,
 }
 
 #[derive(Copy, Clone)]
@@ -155,19 +157,13 @@ impl<'tcx> Visitor<'tcx> for WaitFinder<'_, 'tcx> {
     type NestedFilter = nested_filter::OnlyBodies;
     type Result = ControlFlow<MaybeWait>;
 
-    fn visit_local(&mut self, l: &'tcx LetStmt<'tcx>) -> Self::Result {
-        if self.state == VisitorState::WalkUpToLocal
-            && let PatKind::Binding(_, pat_id, ..) = l.pat.kind
-            && self.local_id == pat_id
-        {
-            self.state = VisitorState::LocalFound;
+    fn visit_expr(&mut self, ex: &'tcx Expr<'tcx>) -> Self::Result {
+        if ex.hir_id == self.create_id {
+            self.state = VisitorState::CreateFound;
+            return Continue(());
         }
 
-        walk_local(self, l)
-    }
-
-    fn visit_expr(&mut self, ex: &'tcx Expr<'tcx>) -> Self::Result {
-        if self.state != VisitorState::LocalFound {
+        if self.state != VisitorState::CreateFound {
             return walk_expr(self, ex);
         }
 

tests/ui/zombie_processes.rs

@@ -198,3 +198,13 @@ mod issue14677 {
         child.wait().unwrap();
     }
 }
+
+fn issue14911() -> std::io::Result<String> {
+    let (mut recv, send) = std::io::pipe()?;
+    let mut command = Command::new("ls")
+        .stdout(send.try_clone()?)
+        .spawn()
+        .expect("Could not spawn new process...");
+    command.wait()?;
+    Ok("".into())
+}