grep: support \s and \S in BRE mode

src/matcher.rs

@@ -215,6 +215,10 @@ impl CompiledPattern {
             // GNU grep supports `{,n}` as an alias for `{0,n}`.
             syntax.enable_behavior(SyntaxBehavior::SYNTAX_BEHAVIOR_ALLOW_INTERVAL_LOW_ABBREV);
         }
+        if config.regex_mode == RegexMode::Basic {
+            // GNU grep treats `\s` and `\S` as whitespace shorthands in BRE mode.
+            syntax.enable_operators(SyntaxOperator::SYNTAX_OPERATOR_ESC_S_WHITE_SPACE);
+        }
         if config.regex_mode == RegexMode::Perl {
             // GNU grep supports `(?P<name>...)`.
             // Unfortunately, the onig crate defines the OP2 flag without the

tests/test_grep.rs

@@ -39,7 +39,7 @@ fn bre_default_metacharacters() {
 
 #[test]
 fn bre_gnu_extensions() {
-    // \+ \? \| \{m,n\} \< \> \b \w plus backreferences and leading `*`.
+    // \+ \? \| \{m,n\} \< \> \b \w \s \S plus backreferences and leading `*`.
     let (_s, mut c) = ucmd();
     c.args(&[r"o\+"])
         .pipe_in("o\noo\nx\n")
@@ -70,6 +70,18 @@ fn bre_gnu_extensions() {
         .succeeds()
         .stdout_only("contain\n");
 
+    let (_s, mut c) = ucmd();
+    c.args(&[r"\s"])
+        .pipe_in("a b\nxy\n")
+        .succeeds()
+        .stdout_only("a b\n");
+
+    let (_s, mut c) = ucmd();
+    c.args(&["-c", r"\S"])
+        .pipe_in("aS b\n  \nx\n")
+        .succeeds()
+        .stdout_only("2\n");
+
     // BRE backreference: repeated adjacent word.
     let (_s, mut c) = ucmd();
     c.args(&[r"\(\b\w\+\b\) \1"])