fix(cli): --help prints usage to stdout and exits 0 (#254)

Asking for help is not an error, but `designcraft-cli --help` shared the
catch-all arm with unknown commands, so it wrote the usage block to
stderr and exited 1 — unusable in a pipeline and wrong by convention
(`--version` already exits 0).

Split the arm: `--help`, `-h` and `help` now print the same usage block
to stdout and succeed, while an unknown command keeps it on stderr and
still fails. The usage text and links line are hoisted into a shared
`USAGE` const and `usage_footer()` so the two paths can't drift.

Fixes #243

🤖 Generated with Codebuff

Co-authored-by: Codebuff <[email protected]>
Co-authored-by: Brandon Thomas <[email protected]>
Co-authored-by: Claude Opus 5.5 <[email protected]>

apps/designcraft-cli/src/main.rs

@@ -34,6 +34,19 @@ mod perf;
 use designcraft_engine::Session;
 use serde_json::{Value, json};
 
+/// The usage block. Shared by `--help` (stdout, success) and an unknown command (stderr, failure).
+const USAGE: &str = "usage: designcraft-cli run [--in FILE | --sample] [--cmd ID[=JSON]]... [--page N] [--scale S] [--pdf-options JSON] [--export OUT] [--all-pages DIR]\n         (--page, --scale and --pdf-options apply to the exports that follow them)\n       designcraft-cli commands [FILTER]\n       designcraft-cli describe COMMAND\n       designcraft-cli script [FILE|-] [--in FILE | --sample] [--connect PORT] [--save OUT] [--export OUT] [--keep-going]\n       designcraft-cli app [--port PORT] COMMAND [JSON] | --method METHOD [JSON]\n       designcraft-cli mcp [--connect PORT] [--sample]\n       designcraft-cli perf [--pages N] [--runs N] [--strict]\n       designcraft-cli bench FILE [--runs N]\n       designcraft-cli links\n       designcraft-cli --version";
+
+/// The links line under the usage block.
+fn usage_footer() -> String {
+    format!(
+        "\nCommunity: {}  ·  {}  ·  {}",
+        designcraft_engine::links::DISCORD,
+        designcraft_engine::links::APP_PAGE,
+        designcraft_engine::links::GITHUB
+    )
+}
+
 /// stdout went away. A reader that stopped early (a closed pipe) ends the program quietly, as
 /// ripgrep does; any other write error is reported.
 fn stdout_failed(e: std::io::Error) -> ! {
@@ -76,16 +89,16 @@ fn main() -> ExitCode {
             outln!("Discord   {DISCORD}\nWebsite   {WEBSITE}\nApp page  {APP_PAGE}\nGitHub    {GITHUB}\nIssues    {ISSUES}");
             ExitCode::SUCCESS
         }
+        // Asking for help is not an error: it goes to stdout and succeeds. An unknown command
+        // still prints the same usage to stderr and fails.
+        Some("--help" | "-h" | "help") => {
+            outln!("{USAGE}");
+            outln!("{}", usage_footer());
+            ExitCode::SUCCESS
+        }
         _ => {
-            eprintln!(
-                "usage: designcraft-cli run [--in FILE | --sample] [--cmd ID[=JSON]]... [--page N] [--scale S] [--pdf-options JSON] [--export OUT] [--all-pages DIR]\n         (--page, --scale and --pdf-options apply to the exports that follow them)\n       designcraft-cli commands [FILTER]\n       designcraft-cli describe COMMAND\n       designcraft-cli script [FILE|-] [--in FILE | --sample] [--connect PORT] [--save OUT] [--export OUT] [--keep-going]\n       designcraft-cli app [--port PORT] COMMAND [JSON] | --method METHOD [JSON]\n       designcraft-cli mcp [--connect PORT] [--sample]\n       designcraft-cli perf [--pages N] [--runs N] [--strict]\n       designcraft-cli bench FILE [--runs N]\n       designcraft-cli links\n       designcraft-cli --version"
-            );
-            eprintln!(
-                "\nCommunity: {}  ·  {}  ·  {}",
-                designcraft_engine::links::DISCORD,
-                designcraft_engine::links::APP_PAGE,
-                designcraft_engine::links::GITHUB
-            );
+            eprintln!("{USAGE}");
+            eprintln!("{}", usage_footer());
             ExitCode::FAILURE
         }
     }

apps/designcraft-cli/tests/cli.rs

@@ -67,6 +67,26 @@ fn run_cmd_references_and_describe() {
     assert!(v.as_array().unwrap().iter().all(|c| c.to_string().contains("footnote")));
 }
 
+/// `designcraft-cli --help` printed usage to stderr and exited 1; asking for help is not an
+/// error (#243). It now goes to stdout and succeeds, while an unknown command keeps the same
+/// usage on stderr and fails.
+#[test]
+fn help_goes_to_stdout_and_unknown_args_to_stderr() {
+    for flag in ["--help", "-h", "help"] {
+        let out = cli().arg(flag).output().unwrap();
+        let stdout = String::from_utf8_lossy(&out.stdout);
+        assert!(out.status.success(), "{flag}: {:?}", out.status);
+        assert!(stdout.starts_with("usage: designcraft-cli"), "{flag}: {stdout:?}");
+        assert!(stdout.contains("designcraft-cli --version"), "{flag}: {stdout:?}");
+        assert!(out.stderr.is_empty(), "{flag} wrote to stderr: {}", String::from_utf8_lossy(&out.stderr));
+    }
+    // An unknown option is still an error: usage on stderr, nothing on stdout, non-zero exit.
+    let out = cli().arg("--no-such-option").output().unwrap();
+    assert!(!out.status.success(), "{:?}", out.status);
+    assert!(out.stdout.is_empty(), "unexpected stdout: {}", String::from_utf8_lossy(&out.stdout));
+    assert!(String::from_utf8_lossy(&out.stderr).starts_with("usage: designcraft-cli"));
+}
+
 /// `designcraft-cli commands | head -1` panicked with "failed printing to
 /// stdout: Broken pipe (os error 32)" and exit status 101.
 #[test]