feat: support subshells

mod.test.ts

@@ -1124,6 +1124,47 @@ Deno.test("piping in command", async () => {
   }
 });
 
+Deno.test("subshells", async () => {
+  {
+    const result = await $`(echo 1 && echo 2) | cat -`.text();
+    assertEquals(result, "1\n2");
+  }
+  {
+    const result = await $`(echo 1 && echo 2) && echo 3`.text();
+    assertEquals(result, "1\n2\n3");
+  }
+  {
+    const result = await $`(echo 1 && echo 2) || echo 3`.text();
+    assertEquals(result, "1\n2");
+  }
+  {
+    const result = await $`echo 1 && (echo 2 || echo 3)`.text();
+    assertEquals(result, "1\n2");
+  }
+  {
+    const result = await $`echo 1 && (echo 2 && echo 3) || echo 4`.text();
+    assertEquals(result, "1\n2\n3");
+  }
+  {
+    const result = await $`echo 1 && (echo 2 || echo 3) && echo 4`.text();
+    assertEquals(result, "1\n2\n4");
+  }
+  // exiting shouldn't exit the parent
+  {
+    const result = await $`echo 1 && (echo 2 && exit 0 && echo 3) && echo 4`.noThrow().text();
+    assertEquals(result, "1\n2\n4");
+  }
+  {
+    const result = await $`echo 1 && (echo 2 && exit 1 && echo 3) || echo 4`.noThrow().text();
+    assertEquals(result, "1\n2\n4");
+  }
+  // shouldn't change the environment either
+  {
+    const result = await $`echo 1 && (echo 2 && export VAR=5 && echo $VAR) && echo $VAR`.text();
+    assertEquals(result, "1\n2\n5\n");
+  }
+});
+
 Deno.test("output redirects", async () => {
   await withTempDir(async (tempDir) => {
     // absolute

src/shell.ts

@@ -49,7 +49,7 @@ export interface Command {
   redirect: Redirect | undefined;
 }
 
-export type CommandInner = SimpleCommand | TaggedSequentialList;
+export type CommandInner = SimpleCommand | Subshell;
 
 export interface SimpleCommand {
   kind: "simple";
@@ -81,8 +81,8 @@ export interface Quoted {
   value: WordPart[];
 }
 
-export interface TaggedSequentialList extends SequentialList {
-  kind: "sequentialList";
+export interface Subshell extends SequentialList {
+  kind: "subshell";
 }
 
 export interface PipeSequence {
@@ -873,9 +873,12 @@ function executeCommandInner(command: CommandInner, context: Context): Promise<E
   switch (command.kind) {
     case "simple":
       return executeSimpleCommand(command, context);
-    case "sequentialList":
-    default:
-      throw new Error(`Not implemented: ${command.kind}`);
+    case "subshell":
+      return executeSubshell(command, context);
+    default: {
+      const _assertNever: never = command;
+      throw new Error(`Not implemented: ${(command as CommandInner).kind}`);
+    }
   }
 }
 
@@ -1011,6 +1014,12 @@ async function executeCommandArgs(commandArgs: string[], context: Context): Prom
   }
 }
 
+async function executeSubshell(subshell: Subshell, context: Context): Promise<ExecuteResult> {
+  const result = await executeSequentialList(subshell, context);
+  // sub shells do not change the environment or cause an exit
+  return { code: result.code, changes: [] };
+}
+
 async function pipeReaderToWritable(reader: Reader, writable: WritableStream<Uint8Array>, signal: AbortSignal) {
   const abortedPromise = new Promise<void>((resolve) => {
     signal.addEventListener("abort", listener);