fix: not finding a command should error in the shell (#257)

mod.test.ts

@@ -192,6 +192,12 @@ Deno.test("should throw when exit code is non-zero", async () => {
   );
 });
 
+Deno.test("should error in the shell when the command can't be found", async () => {
+  const output = await $`nonexistentcommanddaxtest`.noThrow().stderr("piped");
+  assertEquals(output.code, 127);
+  assertEquals(output.stderr, "dax: nonexistentcommanddaxtest: command not found\n");
+});
+
 Deno.test("throws when providing an object that doesn't override toString", async () => {
   {
     const obj1 = {};
@@ -490,11 +496,9 @@ Deno.test("should not allow invalid command names", () => {
 
 Deno.test("should unregister commands", async () => {
   const builder = new CommandBuilder().unregisterCommand("export").noThrow();
-  await assertRejects(
-    async () => await builder.command("export somewhere"),
-    Error,
-    "Command not found: export",
-  );
+  const output = await builder.command("export somewhere").stderr("piped");
+  assertEquals(output.code, 127);
+  assertEquals(output.stderr, "dax: export: command not found\n");
 });
 
 Deno.test("sleep command", async () => {
@@ -1438,7 +1442,7 @@ Deno.test("shebang support", async (t) => {
             .text();
         },
         Error,
-        "Command not found: deno run",
+        "Exited with code: 127",
       );
     });
 

src/shell.ts

@@ -928,6 +928,10 @@ async function executeUnresolvedCommand(
   context: Context,
 ): Promise<ExecuteResult> {
   const resolvedCommand = await resolveCommand(unresolvedCommand, context);
+  if (resolvedCommand === false) {
+    context.stderr.writeLine(`dax: ${unresolvedCommand.name}: command not found`);
+    return { code: 127 };
+  }
   if (resolvedCommand.kind === "shebang") {
     return executeUnresolvedCommand(resolvedCommand.command, [...resolvedCommand.args, ...commandArgs], context);
   }
@@ -1113,7 +1117,7 @@ function pipeCommandPipeReaderToWriterSync(
   }
 }
 
-type ResolvedCommand = ResolvedPathCommand | ResolvedShebangCommand;
+type ResolvedCommand = ResolvedPathCommand | ResolvedShebangCommand | false;
 
 interface ResolvedPathCommand {
   kind: "path";
@@ -1141,7 +1145,7 @@ async function resolveCommand(unresolvedCommand: UnresolvedCommand, context: Con
     // won't have a script with a shebang in it on Windows
     const result = await getExecutableShebangFromPath(commandPath);
     if (result === false) {
-      throw new Error(`Command not found: ${unresolvedCommand.name}`);
+      return false;
     } else if (result != null) {
       const args = await parseShebangArgs(result, context);
       const name = args.shift()!;
@@ -1180,7 +1184,7 @@ async function resolveCommand(unresolvedCommand: UnresolvedCommand, context: Con
     },
   });
   if (commandPath == null) {
-    throw new Error(`Command not found: ${unresolvedCommand.name}`);
+    return false;
   }
   return {
     kind: "path",