1 files changed, 88 insertions, 0 deletions
diff --git a/macros/src/util.rs b/macros/src/util.rs
new file mode 100644
index 00000000..c8c56a05
--- /dev/null
+++ b/macros/src/util.rs
@@ -0,0 +1,88 @@
+use super::*;
+
+/// Return an error at the given item.
+macro_rules! bail {
+    (callsite, $fmt:literal $($tts:tt)*) => {
+        return Err(syn::Error::new(
+            proc_macro2::Span::call_site(),
+            format!(concat!("typst: ", $fmt) $($tts)*)
+        ))
+    };
+    ($item:expr, $fmt:literal $($tts:tt)*) => {
+        return Err(syn::Error::new_spanned(
+            &$item,
+            format!(concat!("typst: ", $fmt) $($tts)*)
+        ))
+    };
+}
+
+/// Whether an attribute list has a specified attribute.
+pub fn has_attr(attrs: &mut Vec<syn::Attribute>, target: &str) -> bool {
+    take_attr(attrs, target).is_some()
+}
+
+/// Whether an attribute list has a specified attribute.
+pub fn parse_attr<T: Parse>(
+    attrs: &mut Vec<syn::Attribute>,
+    target: &str,
+) -> Result<Option<Option<T>>> {
+    take_attr(attrs, target)
+        .map(|attr| (!attr.tokens.is_empty()).then(|| attr.parse_args()).transpose())
+        .transpose()
+}
+
+/// Whether an attribute list has a specified attribute.
+pub fn take_attr(
+    attrs: &mut Vec<syn::Attribute>,
+    target: &str,
+) -> Option<syn::Attribute> {
+    attrs
+        .iter()
+        .position(|attr| attr.path.is_ident(target))
+        .map(|i| attrs.remove(i))
+}
+
+/// Ensure that no unrecognized attributes remain.
+pub fn validate_attrs(attrs: &[syn::Attribute]) -> Result<()> {
+    for attr in attrs {
+        if !attr.path.is_ident("doc") {
+            let ident = attr.path.get_ident().unwrap();
+            bail!(ident, "unrecognized attribute: {:?}", ident.to_string());
+        }
+    }
+    Ok(())
+}
+
+/// Convert an identifier to a kebab-case string.
+pub fn kebab_case(name: &Ident) -> String {
+    name.to_string().to_lowercase().replace('_', "-")
+}
+
+/// Dedent documentation text.
+pub fn dedent(text: &str) -> String {
+    text.lines()
+        .map(|s| s.strip_prefix("  ").unwrap_or(s))
+        .collect::<Vec<_>>()
+        .join("\n")
+}
+
+/// Extract documentation comments from an attribute list.
+pub fn documentation(attrs: &[syn::Attribute]) -> String {
+    let mut doc = String::new();
+
+    // Parse doc comments.
+    for attr in attrs {
+        if let Ok(syn::Meta::NameValue(meta)) = attr.parse_meta() {
+            if meta.path.is_ident("doc") {
+                if let syn::Lit::Str(string) = &meta.lit {
+                    let full = string.value();
+                    let line = full.strip_prefix(' ').unwrap_or(&full);
+                    doc.push_str(line);
+                    doc.push('\n');
+                }
+            }
+        }
+    }
+
+    doc.trim().into()
+}