use codegen, instead of build.rs, to build header file

xtask/src/main.rs

@@ -0,0 +1,47 @@
+//! This executable defines the `cargo xtask` subcommands.
+//!
+//! At the moment it is very simple, but if this grows more subcommands then
+//! it will be sensible to use `clap` or another similar library.
+
+use cbindgen::*;
+use std::env;
+use std::path::PathBuf;
+
+pub fn main() -> anyhow::Result<()> {
+    let arg = env::args().nth(1);
+    match arg.as_ref().map(|arg| arg.as_str()) {
+        Some("codegen") => codegen(),
+        Some(arg) => anyhow::bail!("unknown xtask {}", arg),
+        _ => anyhow::bail!("unknown xtask"),
+    }
+}
+
+/// `cargo xtask codegen`
+///
+/// This uses cbindgen to generate `lib/taskchampion.h`.
+fn codegen() -> anyhow::Result<()> {
+    let manifest_dir = PathBuf::from(env::var("CARGO_MANIFEST_DIR").unwrap());
+    let workspace_dir = manifest_dir.parent().unwrap();
+    let lib_crate_dir = workspace_dir.join("lib");
+
+    Builder::new()
+        .with_crate(&lib_crate_dir)
+        .with_config(Config {
+            language: Language::C,
+            cpp_compat: true,
+            sys_includes: vec!["stdbool.h".into(), "stdint.h".into(), "time.h".into()],
+            usize_is_size_t: true,
+            no_includes: true,
+            enumeration: EnumConfig {
+                // this appears to still default to true for C
+                enum_class: false,
+                ..Default::default()
+            },
+            ..Default::default()
+        })
+        .generate()
+        .expect("Unable to generate bindings")
+        .write_to_file(lib_crate_dir.join("taskchampion.h"));
+
+    Ok(())
+}