Added object metadata & references

lib/typst/local/handout/0.1.0/handout.typ

@@ -151,34 +151,96 @@
 // MARK: Sections
 //
 
-#let generic(t) = block(
+/// Core render code for all objects (problems, theorems, etc)
+/// This should never be used directly by client code.
+///
+/// Args:
+/// - kind: the kind of object to make ("Problem", "Definition", etc)
+/// - label_name: a string. If provided, generate metadata for this object
+///   under the given label. Labels must be unique, and are prefixed with `obj`
+///   This label can then be used to reference this object.
+///
+/// For example:
+/// ```
+/// #problem(label: "problem1")
+/// This is @obj:problem1
+/// ```
+#let _obj_base(kind, ..args, label_name: none) = {
+  counter("obj").step()
+  let n = context counter("obj").get().first()
+
+  // The complete title text of this object,
+  // like "Problem 5:" or "Theorem: "
+  let obj_content = if args.pos().len() == 0 {
+    [#kind #n:]
+  } else {
+    [#kind #n: #args.pos().at(0)]
+  }
+
+  // Render the object
+  block(
     above: 8mm,
     below: 2mm,
-  text(weight: "bold", t),
+    text(weight: "bold", obj_content),
-)
-
-#let _generic_base(kind, ..args) = {
-  counter("obj").step()
-  if args.pos().len() == 0 {
-    generic([
-      #kind
-      #context counter("obj").display():
-    ])
-  } else {
-    generic(
-      [
-        #kind
-        #context counter("obj").display():
-      ]
-        + " "
-        + args.pos().at(0),
   )
+
+  // Generate labeled metadata for this object.
+  //
+  // This can be viewed directly with `#context query(<label>).first().value`,
+  // Or referenced with `@label` (we define a custom renderer for this metadata later)
+  if label_name != none {
+    let label_name = "obj:" + label_name
+    let meta = (
+      "obj_meta_ref_kind": kind,
+      // "obj_content": obj_content,
+      "label": label(label_name),
+      "counter": counter("obj"),
+    )
+    [ #metadata(meta) #label(label_name) ]
   }
 }
 
-#let problem(..args) = _generic_base("Problem", ..args)
+// `ref` implementation for object meta-references,
-#let definition(..args) = _generic_base("Definition", ..args)
+// see `show: ref`.
-#let theorem(..args) = _generic_base("Theorem", ..args)
+#let _ref_obj(it) = {
+  let magic_key = "obj_meta_ref_kind"
+  if not (
+    it.element != none
+      and it.element.has("value")
+      and type(it.element.value) == "dictionary"
+      and it.element.value.keys().contains(magic_key)
+  ) {
+    // This label is not attached to object metadata
+    return none
+  }
+
+  let v = it.element.value
+  let obj_type = v.at(magic_key)
+
+  // The value of this object's counter at its label
+  let obj_count = v.counter.at(v.label).first()
+
+  // Produces text like "Problem 2",
+  // which takes you to the referenced object when clicked.
+  link(v.label, [#obj_type #obj_count])
+}
+
+/// Factory function for objects.
+/// Provided for convenience, lets us define objects in one line.
+#let _mkobj(kind) = {
+  let out(..args, label: none) = _obj_base(
+    kind,
+    ..args,
+    label_name: label,
+  )
+
+  return out
+}
+
+
+#let problem = _mkobj("Problem")
+#let definition = _mkobj("Definition")
+#let theorem = _mkobj("Theorem")
 
 
 //
@@ -272,6 +334,14 @@
     ]
   }
 
+  show ref: it => {
+    // Custom impl for object references
+    let x = _ref_obj(it)
+    if (x != none) { return x }
+
+    return it // Use default `ref` implementation
+  }
+
   make_title(
     group,
     quarter,