pdfcraft-cli --help lists `mcp` only when the build has it (#574)

Follow-up to #540: a build without the `mcp` feature (`--no-default-features`) still listed
`pdfcraft-cli mcp` in its usage, and `pdfcraft-cli mcp` then said "unknown command".

USAGE is now put together with `concat!`, and its `mcp` lines come from a macro that is empty
without the feature. In such a build `pdfcraft-cli mcp` says the MCP server was left out instead
of calling it an unknown command.

- tests/help.rs: usage_lists_mcp_only_when_built_with_it (runs in both feature sets) and
  mcp_without_the_feature_says_it_was_left_out (without the feature)

Co-authored-by: lloyd <lloyd@stackworx.io>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
Co-authored-by: Brandon Thomas <echelon@gmail.com>

apps/pdfcraft-cli/src/main.rs

@@ -26,8 +26,26 @@ use std::time::{Duration, Instant};
 use pdfcraft_engine::export::ImageFormat;
 use pdfcraft_render::{PageRenderer, RenderConfig, RenderRequest, RequestKind, inspect};
 
+/// The `mcp` lines of [`USAGE`]: only a build with the `mcp` feature has the command.
+#[cfg(feature = "mcp")]
+macro_rules! mcp_usage {
+    () => {
+        "\
+pdfcraft-cli mcp    [--root DIR] [--compact]              MCP server on stdin/stdout (opt-in)
+                                                           --compact lists a core set of tools plus tool_search and tool_call
+"
+    };
+}
+#[cfg(not(feature = "mcp"))]
+macro_rules! mcp_usage {
+    () => {
+        ""
+    };
+}
+
 /// The full usage, printed by `--help` (also after a command, e.g. `render --help`).
-const USAGE: &str = "\
+const USAGE: &str = concat!(
+    "\
 pdfcraft-cli info   <file.pdf> [--password PW]            document summary as JSON
 pdfcraft-cli render <file.pdf> --page N [--dpi 96] --out x.png   (.png, .jpg, .tif or .pam)
 pdfcraft-cli text   <file.pdf> [--page N]                  extracted text (pages separated by form feeds)
@@ -40,11 +58,13 @@ pdfcraft-cli check  <files or dirs…> [--timeout 20] [--dpi 36] [--json out.jso
 pdfcraft-cli tools                                       automation tools and their JSON Schemas
 pdfcraft-cli run    <tool> [key=value …] [--root DIR] [--out image.png]
 pdfcraft-cli run    --script steps.json [--root DIR]      [{\"tool\": \"doc_open\", \"args\": {…}}, …]
-pdfcraft-cli mcp    [--root DIR] [--compact]              MCP server on stdin/stdout (opt-in)
-                                                           --compact lists a core set of tools plus tool_search and tool_call
+",
+    mcp_usage!(),
+    "\
 pdfcraft-cli ui     --control FILE <method> [key=value …] [--out shot.png]
                                                            drive a running app started with --control FILE
-help and feedback: https://discord.gg/artcraft";
+help and feedback: https://discord.gg/artcraft"
+);
 
 fn main() -> ExitCode {
     let args: Vec<String> = std::env::args().skip(1).collect();
@@ -70,6 +90,8 @@ fn main() -> ExitCode {
         Some("ui") => ui(&args[1..]),
         #[cfg(feature = "mcp")]
         Some("mcp") => mcp(&args[1..]),
+        #[cfg(not(feature = "mcp"))]
+        Some("mcp") => Err("mcp: this build leaves out the MCP server (built without the `mcp` feature)".into()),
         Some("--version") => version(),
         Some(other) => Err(format!("unknown command '{other}'; see pdfcraft-cli --help").into()),
     };

apps/pdfcraft-cli/tests/help.rs

@@ -34,6 +34,27 @@ fn no_command_fails_with_usage_on_stderr() {
     assert!(text(&out.stderr).contains("pdfcraft-cli render <file.pdf> --page N"));
 }
 
+/// `mcp` is listed only when the build has it (`--no-default-features` leaves it out).
+#[test]
+fn usage_lists_mcp_only_when_built_with_it() {
+    let out = run(&["--help"]);
+    let stdout = text(&out.stdout);
+    assert_eq!(stdout.contains("pdfcraft-cli mcp"), cfg!(feature = "mcp"), "{stdout}");
+    assert_eq!(stdout.contains("--compact"), cfg!(feature = "mcp"), "{stdout}");
+    // The lines around it are still there.
+    assert!(stdout.contains("pdfcraft-cli run    --script steps.json"), "{stdout}");
+    assert!(stdout.contains("pdfcraft-cli ui     --control FILE"), "{stdout}");
+}
+
+#[cfg(not(feature = "mcp"))]
+#[test]
+fn mcp_without_the_feature_says_it_was_left_out() {
+    let out = run(&["mcp"]);
+    assert!(!out.status.success());
+    let stderr = text(&out.stderr);
+    assert!(stderr.contains("without the `mcp` feature"), "{stderr}");
+}
+
 #[test]
 fn unknown_command_names_it_and_points_to_help() {
     let out = run(&["frobnicate"]);