asciidork attribute ref observer sketch

attr_refs.rs.diff

--- a/parser/src/tasks/attr_refs.rs
+++ b/parser/src/tasks/attr_refs.rs
@@ -35,22 +35,30 @@ impl<'arena> Parser<'arena> {
     if token.kind(TokenKind::AttrRef) && self.ctx.subs.attr_refs() {
       match self.document.meta.get(token.attr_name()) {
         Some(AttrValue::String(attr_val)) => {
+          if let Some(observer) = &self.attr_ref_observer {
+            observer.attr_ref_replaced(token.attr_name(), token.loc);
+          }
           if !attr_val.is_empty() {
             self.lexer.set_tmp_buf(attr_val, BufLoc::Repeat(token.loc));
           }
           line.push(token);
         }
-        _ => match self.document.meta.str("attribute-missing") {
-          Some("drop") => {}
-          Some("drop-line") => *drop_line = true,
-          val => {
-            token.kind = TokenKind::Word;
-            if val == Some("warn") {
-              self.err_token_full("Skipping reference to missing attribute", &token)?;
+        _ => {
+          if let Some(observer) = &self.attr_ref_observer {
+            observer.attr_ref_missing(token.attr_name(), token.loc);
+          }
+          match self.document.meta.str("attribute-missing") {
+            Some("drop") => {}
+            Some("drop-line") => *drop_line = true,
+            val => {
+              token.kind = TokenKind::Word;
+              if val == Some("warn") {
+                self.err_token_full("Skipping reference to missing attribute", &token)?;
+              }
+              line.push(token);
             }
-            line.push(token);
           }
-        },
+        }
       }
     } else {
       line.push(token);

parser.rs.diff

--- a/parser/src/parser.rs
+++ b/parser/src/parser.rs
@@ -12,6 +12,7 @@ pub struct Parser<'arena> {
   pub(super) errors: RefCell<Vec<Diagnostic>>,
   pub(super) strict: bool, // todo: naming...
   pub(super) include_resolver: Option<Box<dyn IncludeResolver>>,
+  pub(super) attr_ref_observer: Option<Box<dyn AttrRefObserver>>,
 }
 
 pub struct ParseResult<'arena> {
@@ -19,6 +20,12 @@ pub struct ParseResult<'arena> {
   pub warnings: Vec<Diagnostic>,
 }
 
+pub trait AttrRefObserver {
+  fn attr_ref_replaced(&self, attr_name: &str, loc: SourceLocation);
+  fn attr_ref_missing(&self, attr_name: &str, loc: SourceLocation);
+}
+
+
 impl<'arena> Parser<'arena> {
   pub fn new(src: BumpVec<'arena, u8>, file: SourceFile, bump: &'arena Bump) -> Self {
     Parser::from_lexer(Lexer::new(src, file, bump))
@@ -39,6 +46,7 @@ impl<'arena> Parser<'arena> {
       strict: true,
       include_resolver: None,
       lexer,
+      attr_ref_observer: None,
     };
     parser.set_source_file_attrs();
     parser
@@ -67,6 +75,10 @@ impl<'arena> Parser<'arena> {
     self.include_resolver = Some(resolver);
   }
 
+  pub fn set_attr_ref_observer(&mut self, observer: Box<dyn AttrRefObserver>) {
+    self.attr_ref_observer = Some(observer);
+  }
+
   pub fn cell_parser(&mut self, src: BumpVec<'arena, u8>, offset: u32) -> Parser<'arena> {
     let mut cell_parser = Parser::new(src, self.lexer.source_file().clone(), self.bump);
     cell_parser.strict = self.strict;