Improve --extension help text, closes #673

doc/fd.1

@@ -145,6 +145,9 @@ This option can be used repeatedly to allow for multiple file types.
 Filter search results by file extension
 .IR ext .
 This option can be used repeatedly to allow for multiple possible file extensions.
+
+If you want to search for files without extension, you can use the regex '^[^.]+$'
+as a normal search pattern.
 .TP
 .BI "\-E, \-\-exclude " pattern
 Exclude files/directories that match the given glob pattern.

src/app.rs

@@ -279,7 +279,9 @@ pub fn build_app() -> App<'static, 'static> {
                 .help("Filter by file extension")
                 .long_help(
                     "(Additionally) filter search results by their file extension. Multiple \
-                         allowable file extensions can be specified.",
+                     allowable file extensions can be specified.\n\
+                     If you want to search for files without extension, \
+                     you can use the regex '^[^.]+$' as a normal search pattern.",
                 ),
         )
         .arg(

tests/tests.rs

@@ -1016,6 +1016,34 @@ fn test_extension() {
     te4.assert_output(&["--hidden", "--extension", ".hidden"], "test.hidden");
 }
 
+/// No file extension (test for the pattern provided in the --help text)
+#[test]
+fn test_no_extension() {
+    let te = TestEnv::new(
+        DEFAULT_DIRS,
+        &["a.foo", "aa", "one/b.foo", "one/bb", "one/two/three/d"],
+    );
+
+    te.assert_output(
+        &["^[^.]+$"],
+        "aa
+        one
+        one/bb
+        one/two
+        one/two/three
+        one/two/three/d
+        one/two/three/directory_foo
+        symlink",
+    );
+
+    te.assert_output(
+        &["^[^.]+$", "--type", "file"],
+        "aa
+        one/bb
+        one/two/three/d",
+    );
+}
+
 /// Symlink as search directory
 #[test]
 fn test_symlink_as_root() {