Data merge: a file that is not an image does not hide a later image candidate

The image search stopped at the first file that could be read and
checked whether it decodes afterwards. A non-image file at an earlier
candidate (the drive root, or beside the data file) then hid a valid
image beside the data file or the document, and the field was reported
missing. The decode check now runs inside the search, so only an image
ends it.

crates/engine/src/cmd/datamerge/fill.rs

@@ -464,7 +464,7 @@ struct LoadedImage {
 fn load_image(cell: &str, sources: &Sources) -> Option<LoadedImage> {
     let Sources { data_dir, doc_dir, images, .. } = *sources;
     let cands = image_candidates(cell, data_dir, doc_dir);
-    let (path, bytes) = cands.iter().find_map(|p| {
+    cands.iter().find_map(|p| {
         // Read once per merge: many records naming one file is the normal case, and reading it
         // per record is the amplification (#1595).
         let bytes = images.get_or_read(p, || {
@@ -475,10 +475,11 @@ fn load_image(cell: &str, sources: &Sources) -> Option<LoadedImage> {
             }
             crate::io::read_file(p).ok().filter(|b| !b.is_empty())
         })?;
-        Some((p.clone(), bytes))
-    })?;
-    let (pixels, natural) = designcraft_render::image_size(&bytes).zip(designcraft_render::natural_size(&bytes, 0))?;
-    Some(LoadedImage { path, bytes, pixels, natural })
+        // A file that does not decode leaves the search going, so a valid image at a later
+        // candidate is still found.
+        let (pixels, natural) = designcraft_render::image_size(&bytes).zip(designcraft_render::natural_size(&bytes, 0))?;
+        Some(LoadedImage { path: p.clone(), bytes, pixels, natural })
+    })
 }
 
 fn report_missing(report: &mut FillReport, record: u32, field: &str, cell: &str) {

crates/engine/src/cmd/datamerge/tests.rs

@@ -914,6 +914,28 @@ fn an_image_path_with_a_leading_separator_is_found_beside_the_data_file() {
     assert_eq!(r["missingImages"].as_array().map(Vec::len), Some(0), "{r}");
 }
 
+/// A file at an earlier candidate that is not an image does not hide a valid image at a later
+/// one: the search goes on past it.
+#[test]
+fn a_non_image_file_beside_the_data_does_not_hide_the_image_beside_the_document() {
+    let dir = scratch("undecodable-image");
+    let (data, docs) = (dir.join("data"), dir.join("docs"));
+    write(&data.join("pics").join("a.png"), "not an image");
+    write_png_sized(&docs.join("pics").join("a.png"), 12, 12);
+    write(&data.join("cards.csv"), "@Photo\npics/a.png\n");
+    let mut s = Session::new();
+    new_doc(&mut s, 1);
+    exec(&mut s, "data.source.select", json!({"path": data.join("cards.csv")}));
+    exec(&mut s, "file.save", json!({"path": docs.join("layout.designcraft")}));
+    let frame = exec(&mut s, "frame.create", json!({"rect": [36.0, 36.0, 80.0, 80.0], "content": "graphic"}));
+    exec(&mut s, "data.placeholder.add", json!({"field": "Photo", "item": frame["id"]}));
+    exec(&mut s, "data.options", json!({"linkImages": true}));
+    let r = exec(&mut s, "data.merge", json!({}));
+    assert_eq!(r["missingImages"].as_array().map(Vec::len), Some(0), "{r}");
+    let link = graphic_link(&s).unwrap_or_default();
+    assert!(link.contains("docs"), "{link}");
+}
+
 #[test]
 fn single_record_merge_copies_pages_and_leaves_the_template() {
     let mut s = Session::new();