PDF: a placed image whose file is missing is reported as missing (#299)

A linked image that wasn't found on open has no data; the export warning said it could not be decoded. It now says it is missing and names the link.

Co-authored-by: Brandon Thomas <[email protected]>

crates/pdf/src/export.rs

@@ -1259,7 +1259,13 @@ impl Exporter<'_> {
             _ => lossless(&data, fmt, mode),
         };
         if img.is_none() {
-            self.warn(format!("image `{}` could not be decoded and was skipped", asset.name));
+            if data.is_empty() {
+                // A linked file that wasn't found when the document was opened: nothing to decode.
+                let at = asset.link.as_deref().map(|l| format!(" ({l})")).unwrap_or_default();
+                self.warn(format!("image `{}` is missing{at} and was skipped", asset.name));
+            } else {
+                self.warn(format!("image `{}` could not be decoded and was skipped", asset.name));
+            }
         }
         if let Some(image) = &img {
             // Share the original encoded payload. HashMap checks exact bytes after hashing,

crates/pdf/src/tests.rs

@@ -240,6 +240,20 @@ fn place(d: &mut Document, data: Vec<u8>, px: (u32, u32)) {
     d.insert_item(SpreadRef::Doc(0), it, None).unwrap();
 }
 
+/// A placed image whose linked file wasn't found has no data: the warning says it is missing,
+/// not that it could not be decoded.
+#[test]
+fn a_missing_linked_image_is_reported_as_missing() {
+    let mut d = doc_with_text("still here");
+    place(&mut d, Vec::new(), (64, 64));
+    if let Some(a) = d.assets.values_mut().next() {
+        std::sync::Arc::make_mut(a).link = Some("/gone/curtains.jpeg".into());
+    }
+    let r = export_pdf_with_report(&d, &Cache::new(), &PdfOptions::default()).unwrap();
+    assert!(r.warnings.iter().any(|w| w.contains("is missing (/gone/curtains.jpeg) and was skipped")), "{:?}", r.warnings);
+    assert!(!r.warnings.iter().any(|w| w.contains("could not be decoded")), "{:?}", r.warnings);
+}
+
 /// krilla reads PNG, GIF and WebP lazily, so a damaged one passed the exporter's "does it decode"
 /// check and failed the whole export when the PDF was written ("PDF writer error: … unexpected
 /// end of file"). A cut-off download must be skipped with a warning, as a damaged TIFF is.