Metafile import: a file that reaches the most objects one file may hold says so

The reader keeps at most 200,000 objects from one file and stops reading
there. A picture that reaches that count now carries a warning that any
objects after them were not read, and objects dropped past the import's own
object limit carry a warning too.

crates/metafile/src/import/picture.rs

@@ -36,6 +36,13 @@ use crate::{Imported, Kind};
 
 const PATTERNS: &str = "hatched and pattern brushes are filled with their average color";
 const ENDS_EARLY: &str = "the file ends early: what it held was imported";
+const TOO_MANY: &str = "objects past the most one file may hold were left out";
+const AT_LIMIT: &str = "the file reached the most objects one file may hold: any after them were not read";
+
+/// The most items `craft_metafile` keeps from one file (its `MAX_ITEMS`). It stops reading at the
+/// limit and does not say whether more items followed, so a picture holding this many may have
+/// been cut short.
+const READER_ITEMS: usize = 200_000;
 
 /// Points a unit of a WMF without a placeable header (1440 units an inch).
 const WMF_UNIT: f64 = 72.0 / 1440.0;
@@ -243,7 +250,7 @@ impl Mapper {
 
     fn push(&mut self, clips: Vec<Arc<Clip>>, mut node: Node) {
         if self.out.len() >= MAX_NODES {
-            return;
+            return self.warn(TOO_MANY);
         }
         if !node.visual_bounds().is_none_or(sane) {
             return self.warn(FAR_AWAY);
@@ -526,6 +533,9 @@ pub(crate) fn import(bytes: &[u8]) -> Result<Imported, String> {
     if ends_early(bytes, kind) {
         m.warn(ENDS_EARLY);
     }
+    if pic.items.len() >= READER_ITEMS {
+        m.warn(AT_LIMIT);
+    }
     for item in pic.items {
         m.item(item);
     }

crates/metafile/src/tests/import.rs

@@ -370,6 +370,18 @@ fn damaged_files_fail_or_import_partly() {
     assert!(import(&huge).is_ok());
 }
 
+#[test]
+fn a_file_with_more_objects_than_are_read_says_so() {
+    // RECTANGLE records: 10 more than the reader keeps, then a few under that.
+    let rect = (43, le(&[0, 0, 100, 100]));
+    let many = hand_emf(5000, 3000, &vec![rect.clone(); 200_010]);
+    let back = import(&many).unwrap();
+    assert_eq!(paths(&back.document).len(), 200_000);
+    assert!(back.warnings.iter().any(|w| w.contains("reached the most objects")), "{:?}", back.warnings);
+    let few = import(&hand_emf(5000, 3000, &vec![rect; 3])).unwrap();
+    assert!(few.warnings.is_empty(), "{:?}", few.warnings);
+}
+
 /// An EMR_STRETCHDIBITS copying `png` (a BI_PNG bitmap) to a 10 × 10 box.
 fn png_stretch_dibits(png: &[u8]) -> Vec<u8> {
     // Bounds; destination, source and its size; the BITMAPINFO and the bits (from the record start);