test(io): a PSB's lnk2/pths/cinf are written as 8B64 with an 8-byte length (#7937)

crates/io/src/psd_export.rs

@@ -2084,6 +2084,35 @@ mod tests {
         assert_eq!(signatures(true), vec![(*b"8B64", *b"FMsk"), (*b"8BIM", *b"Patt")], "a PSB keeps 8B64");
     }
 
+    /// A PSB writes every global block with an 8-byte length as `8B64`, the way Photoshop does:
+    /// kept from a PSD source, `lnk2`, `pths` and `cinf` arrive as `8BIM`, and with that signature
+    /// and the PSB's 8-byte length Photoshop 27.11 refused the whole file (#7937). Blocks with a
+    /// 4-byte length keep `8BIM`, and a PSD keeps `8BIM` throughout.
+    #[test]
+    fn psb_writes_long_length_blocks_as_8b64() {
+        let mut doc = document(4, 4);
+        doc.metadata.psd_global_blocks = vec![
+            (*b"8BIM", *b"cinf", std::sync::Arc::new(vec![0, 0, 0, 16, 0, 0, 0, 0])),
+            (*b"8BIM", *b"pths", std::sync::Arc::new(vec![0, 0, 0, 16, 0, 0, 0, 0])),
+            (*b"8BIM", *b"Patt", std::sync::Arc::new(Vec::new())),
+        ];
+        let written = |force_psb| {
+            let opts = PsdExportOptions { force_psb, ..PsdExportOptions::default() };
+            let bytes = document_to_psd_with(&doc, &opts).0.to_bytes().unwrap();
+            let file = PsdFile::from_bytes(&bytes).unwrap();
+            let blocks = file.global_blocks.iter().map(|b| (b.signature, b.key, b.data.len())).collect::<Vec<_>>();
+            (bytes, blocks)
+        };
+        let (bytes, blocks) = written(true);
+        assert_eq!(blocks, vec![(*b"8B64", *b"cinf", 8), (*b"8B64", *b"pths", 8), (*b"8BIM", *b"Patt", 0)]);
+        // On disk: the signature, the key, then the 8-byte length.
+        let at = bytes.windows(8).position(|w| w == b"8B64cinf").expect("8B64cinf in the file");
+        assert_eq!(bytes.get(at + 8..at + 16), Some(&[0u8, 0, 0, 0, 0, 0, 0, 8][..]));
+        assert!(!bytes.windows(8).any(|w| w == b"8BIMcinf" || w == b"8BIMpths"));
+        let (_, blocks) = written(false);
+        assert_eq!(blocks, vec![(*b"8BIM", *b"cinf", 8), (*b"8BIM", *b"pths", 8), (*b"8BIM", *b"Patt", 0)], "a PSD keeps 8BIM");
+    }
+
     /// A layered document with transparency in the merged image and an alpha channel: the name
     /// and DisplayInfo resources hold one entry per extra channel, the merged transparency first,
     /// as in every file Photoshop opens (one short, Photoshop 27.11 refused the file with "Could