feat(unstable): Deno.ppid (#6539)

cli/ops/runtime.rs

@@ -32,6 +32,7 @@ fn op_start(
     "denoVersion": version::DENO,
     "noColor": !colors::use_color(),
     "pid": std::process::id(),
+    "ppid": ppid(),
     "repl": gs.flags.subcommand == DenoSubcommand::Repl,
     "target": env!("TARGET"),
     "tsVersion": version::TYPESCRIPT,
@@ -78,3 +79,62 @@ fn op_metrics(
     "bytesReceived": m.bytes_received
   })))
 }
+
+fn ppid() -> Value {
+  #[cfg(windows)]
+  {
+    // Adopted from rustup:
+    // https://github.com/rust-lang/rustup/blob/1.21.1/src/cli/self_update.rs#L1036
+    // Copyright Diggory Blake, the Mozilla Corporation, and rustup contributors.
+    // Licensed under either of
+    // - Apache License, Version 2.0
+    // - MIT license
+    use std::mem;
+    use winapi::shared::minwindef::DWORD;
+    use winapi::um::handleapi::{CloseHandle, INVALID_HANDLE_VALUE};
+    use winapi::um::processthreadsapi::GetCurrentProcessId;
+    use winapi::um::tlhelp32::{
+      CreateToolhelp32Snapshot, Process32First, Process32Next, PROCESSENTRY32,
+      TH32CS_SNAPPROCESS,
+    };
+    unsafe {
+      // Take a snapshot of system processes, one of which is ours
+      // and contains our parent's pid
+      let snapshot = CreateToolhelp32Snapshot(TH32CS_SNAPPROCESS, 0);
+      if snapshot == INVALID_HANDLE_VALUE {
+        return serde_json::to_value(-1).unwrap();
+      }
+
+      let mut entry: PROCESSENTRY32 = mem::zeroed();
+      entry.dwSize = mem::size_of::<PROCESSENTRY32>() as DWORD;
+
+      // Iterate over system processes looking for ours
+      let success = Process32First(snapshot, &mut entry);
+      if success == 0 {
+        CloseHandle(snapshot);
+        return serde_json::to_value(-1).unwrap();
+      }
+
+      let this_pid = GetCurrentProcessId();
+      while entry.th32ProcessID != this_pid {
+        let success = Process32Next(snapshot, &mut entry);
+        if success == 0 {
+          CloseHandle(snapshot);
+          return serde_json::to_value(-1).unwrap();
+        }
+      }
+      CloseHandle(snapshot);
+
+      // FIXME: Using the process ID exposes a race condition
+      // wherein the parent process already exited and the OS
+      // reassigned its ID.
+      let parent_id = entry.th32ParentProcessID;
+      serde_json::to_value(parent_id).unwrap()
+    }
+  }
+  #[cfg(not(windows))]
+  {
+    use std::os::unix::process::parent_id;
+    serde_json::to_value(parent_id()).unwrap()
+  }
+}