feat: ability to provide a CommandBuilder to .stdin(...)

mod.test.ts

@@ -787,6 +787,26 @@ Deno.test("piping to stdin", async () => {
     const output = await $`cat`.stdin(tempFile).text();
     assertEquals(output, fileText.trim());
   });
+
+  // command via stdin
+  {
+    const child = $`echo 1 && echo 2`;
+    const result = await $`deno eval 'await Deno.stdin.readable.pipeTo(Deno.stdout.writable);'`
+      .stdin(child)
+      .text();
+    assertEquals(result, "1\n2");
+  }
+
+  // command that exists via stdin
+  {
+    const child = $`echo 1 && echo 2 && exit 1`;
+    const result = await $`deno eval 'await Deno.stdin.readable.pipeTo(Deno.stdout.writable);'`
+      .stdin(child)
+      .stderr("piped")
+      .noThrow();
+    assertEquals(result.code, 1);
+    assertEquals(result.stderr, "stdin pipe broken. Error: Exited with code: 1\n");
+  }
 });
 
 Deno.test("piping to a writable and the command fails", async () => {

src/command.ts

@@ -302,6 +302,10 @@ export class CommandBuilder implements PromiseLike<CommandResult> {
           const body = await reader;
           return body.readable;
         });
+      } else if (reader instanceof CommandBuilder) {
+        state.stdin = new Deferred(() => {
+          return reader.stdout("piped").spawn().stdout();
+        });
       } else {
         state.stdin = new Box(reader);
       }

src/pipes.ts

@@ -2,6 +2,7 @@ import { type FsFileWrapper, PathRef } from "./path.ts";
 import { logger } from "./console/logger.ts";
 import { Buffer, writeAllSync } from "./deps.ts";
 import type { RequestBuilder } from "./request.ts";
+import type { CommandBuilder } from "./command.ts";
 
 const encoder = new TextEncoder();
 
@@ -30,6 +31,7 @@ export type ShellPipeReaderKind =
   | Reader
   | ReadableStream<Uint8Array>
   | Uint8Array
+  | CommandBuilder
   | FsFileWrapper
   | PathRef
   | RequestBuilder;