Add support for BusyBox less as pager (#2162)

* Add support for BusyBox less as pager

* Run tests/syntax-tests/update.sh to update tests

* Address reviewer's concerns with pull request
* Revert all changes in `test` directory
* Minimize overall diff size
* Detect busybox from separate helper function
* Pass equivalent options to BusyBox from same code by changing from long to
  short options

* Remove redundant `if` statement from previous commit
Add test for invalid utf-8
Add `parse_less_version_busybox` to test for invalid program
Add commenting around short options

src/less.rs

@@ -3,21 +3,38 @@
 use std::ffi::OsStr;
 use std::process::Command;
 
-pub fn retrieve_less_version(less_path: &dyn AsRef<OsStr>) -> Option<usize> {
+#[derive(Debug, PartialEq)]
+pub enum LessVersion {
+    Less(usize),
+    BusyBox,
+}
+
+pub fn retrieve_less_version(less_path: &dyn AsRef<OsStr>) -> Option<LessVersion> {
     let resolved_path = grep_cli::resolve_binary(less_path.as_ref()).ok()?;
 
     let cmd = Command::new(resolved_path).arg("--version").output().ok()?;
-    parse_less_version(&cmd.stdout)
+    if cmd.status.success() {
+        parse_less_version(&cmd.stdout)
+    } else {
+        parse_less_version_busybox(&cmd.stderr)
+    }
 }
 
-fn parse_less_version(output: &[u8]) -> Option<usize> {
+fn parse_less_version(output: &[u8]) -> Option<LessVersion> {
     if !output.starts_with(b"less ") {
         return None;
     }
 
     let version = std::str::from_utf8(&output[5..]).ok()?;
     let end = version.find(|c: char| !c.is_ascii_digit())?;
-    version[..end].parse::<usize>().ok()
+    Some(LessVersion::Less(version[..end].parse::<usize>().ok()?))
+}
+
+fn parse_less_version_busybox(output: &[u8]) -> Option<LessVersion> {
+    match std::str::from_utf8(output) {
+        Ok(version) if version.contains("BusyBox ") => Some(LessVersion::BusyBox),
+        _ => None,
+    }
 }
 
 #[test]
@@ -30,7 +47,7 @@ For information about the terms of redistribution,
 see the file named README in the less distribution.
 Homepage: http://www.greenwoodsoftware.com/less";
 
-    assert_eq!(Some(487), parse_less_version(output));
+    assert_eq!(Some(LessVersion::Less(487)), parse_less_version(output));
 }
 
 #[test]
@@ -43,7 +60,7 @@ For information about the terms of redistribution,
 see the file named README in the less distribution.
 Homepage: http://www.greenwoodsoftware.com/less";
 
-    assert_eq!(Some(529), parse_less_version(output));
+    assert_eq!(Some(LessVersion::Less(529)), parse_less_version(output));
 }
 
 #[test]
@@ -56,7 +73,7 @@ For information about the terms of redistribution,
 see the file named README in the less distribution.
 Home page: http://www.greenwoodsoftware.com/less";
 
-    assert_eq!(Some(551), parse_less_version(output));
+    assert_eq!(Some(LessVersion::Less(551)), parse_less_version(output));
 }
 
 #[test]
@@ -69,7 +86,7 @@ For information about the terms of redistribution,
 see the file named README in the less distribution.
 Home page: https://greenwoodsoftware.com/less";
 
-    assert_eq!(Some(581), parse_less_version(output));
+    assert_eq!(Some(LessVersion::Less(581)), parse_less_version(output));
 }
 
 #[test]
@@ -77,4 +94,38 @@ fn test_parse_less_version_wrong_program() {
     let output = b"more from util-linux 2.34";
 
     assert_eq!(None, parse_less_version(output));
+    assert_eq!(None, parse_less_version_busybox(output));
+}
+
+#[test]
+fn test_parse_less_version_busybox() {
+    let output = b"pkg/less: unrecognized option '--version'
+BusyBox v1.35.0 (2022-04-21 10:38:11 EDT) multi-call binary.
+
+Usage: less [-EFIMmNSRh~] [FILE]...
+
+View FILE (or stdin) one screenful at a time
+
+        -E      Quit once the end of a file is reached
+        -F      Quit if entire file fits on first screen
+        -I      Ignore case in all searches
+        -M,-m   Display status line with line numbers
+                and percentage through the file
+        -N      Prefix line number to each line
+        -S      Truncate long lines
+        -R      Remove color escape codes in input
+        -~      Suppress ~s displayed past EOF";
+
+    assert_eq!(
+        Some(LessVersion::BusyBox),
+        parse_less_version_busybox(output)
+    );
+}
+
+#[test]
+fn test_parse_less_version_invalid_utf_8() {
+    let output = b"\xff";
+
+    assert_eq!(None, parse_less_version(output));
+    assert_eq!(None, parse_less_version_busybox(output));
 }