feat: improve InvalidIndexFile error to mention index file names (#1859)

* feat: improve InvalidIndexFile error to mention index file names

this makes it clearer which files are causing the link check to fail.
it also lets us customise the message in the special case of
`--index-files ''`, which could otherwise be confusing with a generic
message.

the messages are:
```
[ERROR] file:///h | Cannot find index file within directory: An index file (index.html) is required
[ERROR] file:///h | Cannot find index file within directory: An index file (index.html, or index.htm) is required
[ERROR] file:///h | Cannot find index file within directory: An index file (index.html, index.htm, or index.md) is required
```

and for the `--index-files ''` case:
```
[ERROR] file:///h | Cannot find index file within directory: No directory links are allowed because index_files is defined and empty
```

i do wonder if this last error message is still confusing because of the
"Cannot find index file within directory" text. maybe it should be
changed to a more general "Cannot resolve link to local directory"?

for comparison, the old message was always:
```
[ERROR] file:///h | Cannot find index file within directory: Index file not found in directory. Check if index.html or other index files exist
```

* move dropping into file.rs

* add some tests

* revert spurious

Author: katrinafyi

lychee-bin/tests/cli.rs

@@ -2546,12 +2546,12 @@ mod cli {
     fn test_index_files_specified() {
         let input = fixtures_path().join("filechecker/dir_links.md");
 
-        // passing `--index-files index.html` should reject all links
+        // passing `--index-files index.html,index.htm` should reject all links
         // to /empty_dir because it doesn't have the index file
         let result = main_command()
-            .arg(input)
+            .arg(&input)
             .arg("--index-files")
-            .arg("index.html")
+            .arg("index.html,index.htm")
             .arg("--verbose")
             .assert()
             .failure();
@@ -2561,7 +2561,18 @@ mod cli {
         result
             .stdout(contains("Cannot find index file").count(empty_dir_links))
             .stdout(contains("/empty_dir").count(empty_dir_links))
+            .stdout(contains("(index.html, or index.htm)").count(empty_dir_links))
             .stdout(contains(format!("{index_dir_links} OK")));
+
+        // within the error message, formatting of the index file name list should
+        // omit empty names.
+        main_command()
+            .arg(&input)
+            .arg("--index-files")
+            .arg(",index.html,,,index.htm,")
+            .assert()
+            .failure()
+            .stdout(contains("(index.html, or index.htm)").count(empty_dir_links));
     }
 
     #[test]
@@ -2601,7 +2612,7 @@ mod cli {
         // passing an empty list to --index-files should reject /all/
         // directory links.
         let result = main_command()
-            .arg(input)
+            .arg(&input)
             .arg("--index-files")
             .arg("")
             .assert()
@@ -2610,6 +2621,17 @@ mod cli {
         let num_dir_links = 4;
         result
             .stdout(contains("Cannot find index file").count(num_dir_links))
+            .stdout(contains("No directory links are allowed").count(num_dir_links))
+            .stdout(contains("0 OK"));
+
+        // ... as should passing a number of empty index file names
+        main_command()
+            .arg(&input)
+            .arg("--index-files")
+            .arg(",,,,,")
+            .assert()
+            .failure()
+            .stdout(contains("No directory links are allowed").count(num_dir_links))
             .stdout(contains("0 OK"));
     }
 

lychee-lib/src/checker/file.rs

@@ -229,6 +229,15 @@ impl FileChecker {
             None => &[".".to_owned()],
         };
 
+        let invalid_index_error = || {
+            // Drop empty index file names. These will never be accepted as valid
+            // index files, and doing this makes cleaner error reporting.
+            let mut names = index_names_to_try.to_vec();
+            names.retain(|x| !x.is_empty());
+
+            ErrorKind::InvalidIndexFile(names)
+        };
+
         index_names_to_try
             .iter()
             .find_map(|filename| {
@@ -242,7 +251,7 @@ impl FileChecker {
                 let path = dir_path.join(filename);
                 exists(&path).then_some(path)
             })
-            .ok_or_else(|| ErrorKind::InvalidIndexFile(dir_path.to_path_buf()))
+            .ok_or_else(invalid_index_error)
     }
 
     /// Checks a resolved file, optionally verifying fragments for HTML files.

lychee-lib/src/types/error.rs

@@ -70,9 +70,9 @@ pub enum ErrorKind {
     #[error("Cannot find fragment")]
     InvalidFragment(Uri),
 
-    /// The given directory is missing a required index file
+    /// Cannot resolve local directory link using the configured index files
     #[error("Cannot find index file within directory")]
-    InvalidIndexFile(PathBuf),
+    InvalidIndexFile(Vec<String>),
 
     /// The given path cannot be converted to a URI
     #[error("Invalid path to URL conversion: {0}")]
@@ -330,9 +330,11 @@ impl ErrorKind {
             ErrorKind::StatusCodeSelectorError(status_code_selector_error) => Some(format!(
                 "Status code selector error: {status_code_selector_error}. Check accept configuration",
             )),
-            ErrorKind::InvalidIndexFile(_path) => Some(
-                "Index file not found in directory. Check if index.html or other index files exist".to_string()
-            ),
+            ErrorKind::InvalidIndexFile(index_files) => match &index_files[..] {
+                [] => "No directory links are allowed because index_files is defined and empty".to_string(),
+                [name] => format!("An index file ({name}) is required"),
+                [init @ .., tail] => format!("An index file ({}, or {}) is required", init.join(", "), tail),
+            }.into()
         }
     }