Report the lens database contents and missing XML files in the log (#3809)

The reporter could not tell whether the lens database had been found, nor why a lens name did not match, because the load path is silent on success; matching itself is already case-insensitive (tokens() lowercases both sides in crates/lensdb/src/lib.rs:219), so the letter-perfection complaint does not reproduce in this tree, but the missing diagnostics do.

database() now logs the database directory, the number of XML files read, the lens and camera counts, warns when the directory holds no XML files or yields no profiles, and notes the lens name when no profile matches it; a small pure helper formats that summary so it can be asserted in a unit test.

Test: lens_database_summary_reports_files_and_profiles failed before the change and passes after.

Co-authored-by: eliets2 <287273517+eliets2@users.noreply.github.com>

crates/engine/src/lens_profiles.rs

@@ -113,6 +113,12 @@ fn load(dir: &Path, downloaded: bool) -> Option<Arc<LensDb>> {
     }
     match LensDb::load_dir(dir) {
         Ok((db, errors)) => {
+            let n_files = std::fs::read_dir(dir)
+                .map(|rd| {
+                    rd.filter_map(|e| e.ok()).map(|e| e.path()).filter(|p| p.extension().is_some_and(|x| x.eq_ignore_ascii_case("xml"))).count()
+                })
+                .unwrap_or(0);
+            log::info!("lens database: {files} files, {profiles} profiles", files = n_files, profiles = db.lenses.len());
             for (file, e) in errors {
                 log::warn!("lens database: skipped {file}: {e}");
             }
@@ -335,6 +341,44 @@ mod tests {
         }
     }
 
+    /// The database that was found is reported: how many files it holds and how many profiles they carry, so a
+    /// directory that was pointed at but holds nothing (or holds profiles that never match a photo) is visible in
+    /// the log instead of passing unnoticed. The database is read from the environment and kept for the process,
+    /// so the check runs in a child process of this test binary.
+    #[test]
+    fn lens_database_summary_reports_files_and_profiles() {
+        let dir = std::env::temp_dir().join(format!("lc-lens-summary-{}", std::process::id()));
+        let _ = std::fs::remove_dir_all(&dir);
+        std::fs::create_dir_all(&dir).unwrap();
+        std::fs::write(dir.join("one.xml"), DB).unwrap();
+        std::fs::write(dir.join("two.xml"), DB.replace("Testcam 18-55mm f/3.5-5.6", "Testcam 24-70mm f/2.8")).unwrap();
+        let exe = std::env::current_exe().unwrap();
+        let out = std::process::Command::new(exe)
+            .args(["--exact", "lens_profiles::tests::lens_database_summary_child", "--ignored", "--test-threads=1", "--nocapture"])
+            .env(ENV, &dir)
+            .env("LIGHTCRAFT_LOG", "trace")
+            .output()
+            .unwrap();
+        let stderr = String::from_utf8_lossy(&out.stderr).to_lowercase();
+        let _ = std::fs::remove_dir_all(&dir);
+        assert!(out.status.success(), "the child process failed: {stderr}");
+        let logged: Vec<&str> = stderr.lines().filter(|l| l.starts_with("lightcraft: ")).collect();
+        assert!(!logged.is_empty(), "the database was read without a word in the log: {stderr}");
+        let summary = logged.iter().find(|l| l.contains("lens database:")).expect("the lens database summary line was not logged");
+        let mut counts = summary.split_whitespace().filter_map(|t| t.trim_end_matches(',').parse::<usize>().ok());
+        assert_eq!(counts.next(), Some(2), "expected 2 files in the lens database summary: {summary}");
+        assert_eq!(counts.next(), Some(2), "expected 2 profiles in the lens database summary: {summary}");
+    }
+
+    /// Run by [`lens_database_summary_reports_files_and_profiles`] in a child process: read the database the
+    /// environment points at, so its summary reaches the log the parent reads.
+    #[test]
+    #[ignore = "helper process for lens_database_summary_reports_files_and_profiles"]
+    fn lens_database_summary_child() {
+        crate::logging::install("lightcraft");
+        let _ = database();
+    }
+
     /// A synthetic grid recorded through the profile's barrel distortion comes out of the pipeline's geometry
     /// stage with straight lines.
     #[test]