grep: honor \s and \S in basic regexps

src/matcher.rs

@@ -277,6 +277,11 @@ impl CompiledPattern {
             // GNU grep supports \` and \' as buffer anchors in BRE and ERE.
             syntax.enable_operators(SyntaxOperator::SYNTAX_OPERATOR_ESC_GNU_BUF_ANCHOR);
         }
+        if config.regex_mode == RegexMode::Basic {
+            // GNU grep supports \s and \S as extensions in BRE, like \w and \W.
+            // `Syntax::grep()` leaves them off, so they parse as literal s / S.
+            syntax.enable_operators(SyntaxOperator::SYNTAX_OPERATOR_ESC_S_WHITE_SPACE);
+        }
 
         if matches!(config.regex_mode, RegexMode::Basic | RegexMode::Extended)
             && has_confusing_bracket(pattern.as_bytes())

tests/test_grep.rs

@@ -100,6 +100,30 @@ fn gnu_buffer_anchors() {
         .stdout_only("cat\ntar\n");
 }
 
+#[test]
+fn whitespace_escapes_in_basic_regexp() {
+    // GNU grep honors \s and \S in BRE as well as ERE, like \w and \W.
+    let input = "a b\nxy\n";
+
+    for args in [
+        vec![r"\s"],
+        vec!["-G", r"\s"],
+        vec!["-E", r"\s"],
+        vec!["-e", r"\s"],
+    ] {
+        let (_s, mut c) = ucmd();
+        c.args(&args).pipe_in(input).succeeds().stdout_only("a b\n");
+    }
+
+    for args in [vec![r"\S"], vec!["-G", r"\S"], vec!["-E", r"\S"]] {
+        let (_s, mut c) = ucmd();
+        c.args(&args)
+            .pipe_in(input)
+            .succeeds()
+            .stdout_only("a b\nxy\n");
+    }
+}
+
 #[test]
 fn ere_metacharacters() {
     let cases: &[(&[&str], &str, &str)] = &[