Do not surface warnings from non-last layout iterations (#4970)

crates/typst/src/engine.rs

@@ -156,6 +156,11 @@ impl Sink {
     pub fn values(self) -> EcoVec<(Value, Option<Styles>)> {
         self.values
     }
+
+    /// Extend from another sink.
+    pub fn extend_from_sink(&mut self, other: Sink) {
+        self.extend(other.delayed, other.warnings, other.values);
+    }
 }
 
 #[comemo::track]
@@ -181,7 +186,7 @@ impl Sink {
         }
     }
 
-    /// Extend from another sink.
+    /// Extend from parts of another sink.
     fn extend(
         &mut self,
         delayed: EcoVec<SourceDiagnostic>,

crates/typst/src/lib.rs

@@ -128,6 +128,7 @@ fn compile_impl(
     .content();
 
     let mut iter = 0;
+    let mut subsink;
     let mut document = Document::default();
 
     // Relayout until all introspections stabilize.
@@ -138,15 +139,14 @@ fn compile_impl(
             &["layout (1)", "layout (2)", "layout (3)", "layout (4)", "layout (5)"];
         let _scope = TimingScope::new(ITER_NAMES[iter], None);
 
-        // Clear delayed errors.
-        sink.delayed();
+        subsink = Sink::new();
 
         let constraint = <Introspector as Validate>::Constraint::new();
         let mut engine = Engine {
             world,
             introspector: document.introspector.track_with(&constraint),
             traced,
-            sink: sink.track_mut(),
+            sink: subsink.track_mut(),
             route: Route::default(),
         };
 
@@ -160,7 +160,7 @@ fn compile_impl(
         }
 
         if iter >= 5 {
-            sink.warn(warning!(
+            subsink.warn(warning!(
                 Span::detached(), "layout did not converge within 5 attempts";
                 hint: "check if any states or queries are updating themselves"
             ));
@@ -168,6 +168,8 @@ fn compile_impl(
         }
     }
 
+    sink.extend_from_sink(subsink);
+
     // Promote delayed errors.
     let delayed = sink.delayed();
     if !delayed.is_empty() {

tests/suite/foundations/context.typ

@@ -76,3 +76,16 @@
 // Warning: 2-44 `counter.display` without context is deprecated
 // Hint: 2-44 use it in a `context` expression instead
 #counter(heading).display(n => test(n, 10))
+
+--- context-delayed-warning ---
+// Ensure that the warning that triggers in the first layout iteration is not
+// surfaced since it goes away in the second one. Just like errors in show
+// rules.
+#show heading: none
+
+= A <a>
+#context {
+  let n = query(<a>).len()
+  let fonts = ("nope", "Roboto")
+  set text(font: fonts.at(n))
+}