💥 Fail stdio create when no input paths are given

Previously `pna experimental stdio -c -f out.pna` with no positional
arguments silently created an empty archive. Bail with an actionable
error message, matching bsdtar behavior.

Author: ChanTsune

cli/src/command/stdio.rs

@@ -850,6 +850,9 @@ fn run_create_archive(args: StdioCommand) -> anyhow::Result<()> {
     if let Some(path) = args.files_from {
         files.extend(read_paths(path, args.null)?);
     }
+    if files.is_empty() {
+        anyhow::bail!("create mode requires at least one input path or @archive source");
+    }
 
     let mut exclude = args.exclude;
     if let Some(p) = args.exclude_from {

cli/tests/cli/stdio.rs

@@ -1,6 +1,7 @@
 mod archive_inclusion;
 mod exclude_vcs;
 mod files_from;
+mod missing_file;
 #[cfg(unix)]
 mod mtree;
 mod option_auto_compress;

cli/tests/cli/stdio/missing_file.rs

@@ -0,0 +1,22 @@
+use crate::utils::setup;
+use assert_cmd::cargo::cargo_bin_cmd;
+
+/// Precondition: No input paths are provided.
+/// Action: Run `pna experimental stdio -c -f ...` without positional paths.
+/// Expectation: Command fails similarly to bsdtar's "missing file" handling.
+#[test]
+fn stdio_create_without_inputs_fails() {
+    setup();
+
+    let mut cmd = cargo_bin_cmd!("pna");
+    cmd.args([
+        "--quiet",
+        "experimental",
+        "stdio",
+        "--unstable",
+        "-c",
+        "-f",
+        "stdio_create_without_inputs_fails.pna",
+    ]);
+    cmd.assert().failure();
+}