fix: stdin := .null in IO.Process.output

RELEASES.md

@@ -10,6 +10,7 @@ Please check the [releases](https://github.com/leanprover/lean4/releases) page f
 v4.3.0 (development in progress)
 ---------
 
+* `IO.Process.output` no longer inherits the standard input of the caller.
 * The derive handler for `DecidableEq` [now handles](https://github.com/leanprover/lean4/pull/2591) mutual inductive types.
 * [Show path of failed import in Lake](https://github.com/leanprover/lean4/pull/2616).
 * [Fix linker warnings on macOS](https://github.com/leanprover/lean4/pull/2598).

src/Init/System/IO.lean

@@ -638,9 +638,12 @@ structure Output where
   stdout   : String
   stderr   : String
 
-/-- Run process to completion and capture output. -/
+/--
+Run process to completion and capture output.
+The process does not inherit the standard input of the caller.
+-/
 def output (args : SpawnArgs) : IO Output := do
-  let child ← spawn { args with stdout := Stdio.piped, stderr := Stdio.piped }
+  let child ← spawn { args with stdout := .piped, stderr := .piped, stdin := .null }
   let stdout ← IO.asTask child.stdout.readToEnd Task.Priority.dedicated
   let stderr ← child.stderr.readToEnd
   let exitCode ← child.wait