xtask: also generate EXAMPLES section

Include "Examples" section from READMEs if they exist into the generated
manual page.

Signed-off-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>

xtask/Cargo.toml

@@ -13,6 +13,7 @@ publish = false
 clap = { version = "4.5", features = ["derive"], optional = true }
 clap_mangen = { version = "0.2.24", optional = true }
 toml = { version = "0.8.19", optional = true }
+markdown = { version = "=1.0.0-alpha.23", optional = true }
 
 [build-dependencies]
 
@@ -22,7 +23,7 @@ vhost-device-scmi = []
 vhost-device-sound = ["vhost-device-sound-alsa", "vhost-device-sound-pipewire"]
 vhost-device-sound-alsa = ["mangen"]
 vhost-device-sound-pipewire = ["mangen"]
-mangen = ["dep:clap_mangen", "dep:clap", "dep:toml"]
+mangen = ["dep:clap_mangen", "dep:clap", "dep:toml", "dep:markdown"]
 
 [lints.rust]
 unexpected_cfgs = { level = "allow", check-cfg = ['cfg(feature, values("alsa-backend", "pw-backend"))'] }

xtask/README.md

@@ -6,6 +6,8 @@ This binary crate provides support for running useful tasks with `cargo xtask <.
 
 The `mangen` task which is enabled by the `mangen` cargo feature, builds ROFF manual pages for binary crates in this repository. It uses the [`clap_mangen`](https://crates.io/crates/clap_mangen) crate to generate ROFF from the crate's argument types which implement the `clap::CommandFactory` trait, through the `clap::Parser` derive macro.
 
+Furthmore, if the `README.md` of a crate contains an `Examples` heading, it includes it in the manual page.
+
 ```session
 $ cargo xtask mangen
     Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.04s

xtask/src/main.rs

@@ -15,6 +15,8 @@ use clap::CommandFactory;
 #[cfg(feature = "mangen")]
 use clap_mangen::Man;
 #[cfg(feature = "mangen")]
+use markdown::{to_mdast, ParseOptions};
+#[cfg(feature = "mangen")]
 use toml::value::Table;
 
 // Use vhost-device-sound's args module as our own using the #[path] attribute
@@ -63,7 +65,19 @@ fn print_help() {
 }
 
 #[cfg(feature = "mangen")]
-fn mangen_for_crate<T: CommandFactory>(manifest: Table) -> Result<Vec<u8>, Box<dyn Error>> {
+fn mangen_for_crate<T: CommandFactory>(
+    crate_dir: std::path::PathBuf,
+) -> Result<Vec<u8>, Box<dyn Error>> {
+    let readme_md = std::fs::read_to_string(crate_dir.join("README.md"))?;
+    let example_text = parse_examples_from_readme(readme_md).unwrap_or_default();
+    let examples = if example_text.is_empty() {
+        None
+    } else {
+        Some(example_text.trim())
+    };
+    let manifest = std::fs::read_to_string(crate_dir.join("Cargo.toml"))?;
+    let manifest = manifest.as_str().parse::<Table>()?;
+
     let name: &'static str = manifest["package"]["name"]
         .as_str()
         .unwrap()
@@ -94,6 +108,14 @@ fn mangen_for_crate<T: CommandFactory>(manifest: Table) -> Result<Vec<u8>, Box<d
     let man = Man::new(cmd);
     let mut buffer: Vec<u8> = Default::default();
     man.render(&mut buffer)?;
+    if let Some(examples) = examples {
+        let mut examples_section = clap_mangen::roff::Roff::new();
+        examples_section.control("SH", ["EXAMPLES"]);
+        for line in examples.lines() {
+            examples_section.text(vec![line.into()]);
+        }
+        examples_section.to_writer(&mut buffer)?;
+    }
     clap_mangen::roff::Roff::new()
         .control("SH", ["REPORTING BUGS"])
         .text(vec![format!(
@@ -105,6 +127,41 @@ fn mangen_for_crate<T: CommandFactory>(manifest: Table) -> Result<Vec<u8>, Box<d
     Ok(buffer)
 }
 
+#[cfg(feature = "mangen")]
+fn parse_examples_from_readme(readme_md: String) -> Result<String, Box<dyn Error>> {
+    use markdown::mdast;
+
+    let mdast = to_mdast(&readme_md, &ParseOptions::gfm()).map_err(|err| err.to_string())?;
+    let mut example_text = String::new();
+    if let mdast::Node::Root(root) = mdast {
+        if let Some(examples_index) = root.children.iter().position(|r| matches!(r, mdast::Node::Heading(mdast::Heading { ref children, .. }) if matches!(children.first(), Some(mdast::Node::Text(mdast::Text { ref value, .. })) if value.trim() == "Examples"))){
+            let mdast::Node::Heading(examples_heading) =
+                &root.children[examples_index]
+                else {
+                    // SAFETY: Unreachable because we found the exact position earlier.
+                    unreachable!();
+                };
+                let depth = examples_heading.depth;
+                let mut i = examples_index + 1;
+                while i < root.children.len() && !matches!(root.children[i], mdast::Node::Heading(ref h) if h.depth >= depth) {
+                    match &root.children[i] {
+                        mdast::Node::Paragraph(p) => {
+                            example_text.push_str(&p.children.iter().map(|t| t.to_string()).collect::<Vec<String>>().join(" "));
+                            example_text.push_str("\n\n");
+                        },
+                        mdast::Node::Code(c) => {
+                            example_text.push_str(&c.value);
+                            example_text.push_str("\n\n");
+                        },
+                        _ => {},
+                    }
+                    i += 1;
+                }
+        }
+    }
+    Ok(example_text)
+}
+
 #[cfg(feature = "mangen")]
 fn mangen() -> Result<(), Box<dyn Error>> {
     let workspace_dir = std::path::Path::new(&env!("CARGO_MANIFEST_DIR"))
@@ -124,11 +181,7 @@ fn mangen() -> Result<(), Box<dyn Error>> {
     {
         use vhost_device_sound::SoundArgs;
 
-        let manifest =
-            std::fs::read_to_string(workspace_dir.join("vhost-device-sound/Cargo.toml"))?;
-        let manifest = manifest.as_str().parse::<Table>()?;
-
-        let buffer = mangen_for_crate::<SoundArgs>(manifest)?;
+        let buffer = mangen_for_crate::<SoundArgs>(workspace_dir.join("vhost-device-sound"))?;
         let man_path = dist_dir.join("vhost-device-sound.1");
         buffers.push((man_path, buffer));
     }
@@ -136,10 +189,7 @@ fn mangen() -> Result<(), Box<dyn Error>> {
     {
         use vhost_device_scmi::ScmiArgs;
 
-        let manifest = std::fs::read_to_string(workspace_dir.join("vhost-device-scmi/Cargo.toml"))?;
-        let manifest = manifest.as_str().parse::<Table>()?;
-
-        let buffer = mangen_for_crate::<ScmiArgs>(manifest)?;
+        let buffer = mangen_for_crate::<ScmiArgs>(workspace_dir.join("vhost-device-scmi"))?;
         let man_path = dist_dir.join("vhost-device-scmi.1");
         buffers.push((man_path, buffer));
     }