grep: don't short-circuit -v empty pattern under -x/-w

src/lib.rs

@@ -445,8 +445,15 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
     }
 
     // An empty pattern matches every line; with `-v`, GNU grep selects no lines
-    // and exits as "no match" without reading any input files.
-    if invert_match && patterns.iter().any(|pattern| pattern.is_empty()) {
+    // and exits as "no match" without reading any input files. This does not
+    // hold under `-x` or `-w`, where an empty pattern matches only an empty
+    // line or an empty match at a word boundary, so the inversion still selects
+    // the remaining lines and the input has to be read.
+    if invert_match
+        && !word_regexp
+        && !line_regexp
+        && patterns.iter().any(|pattern| pattern.is_empty())
+    {
         return Err(ExitCode::new(1));
     }
 

tests/test_grep.rs

@@ -674,6 +674,30 @@ fn empty_pattern_matches_every_line() {
         .stdout_only("a\nb\nc\n");
 }
 
+#[test]
+fn inverted_empty_pattern_does_not_short_circuit_under_x_or_w() {
+    // Under `-x` the empty pattern matches only an empty line, and under `-w`
+    // only an empty match at a word boundary, so `-v` still selects the rest.
+    let (_s, mut c) = ucmd();
+    c.args(&["-e", "", "-x", "-v"])
+        .pipe_in("abc\ndef\n")
+        .succeeds()
+        .stdout_only("abc\ndef\n");
+
+    let (_s, mut c) = ucmd();
+    c.args(&["-e", "", "-w", "-v"])
+        .pipe_in("abc\ndef\n")
+        .succeeds()
+        .stdout_only("abc\ndef\n");
+
+    // `-x` still drops the empty line itself.
+    let (_s, mut c) = ucmd();
+    c.args(&["-e", "", "-x", "-v"])
+        .pipe_in("abc\n\ndef\n")
+        .succeeds()
+        .stdout_only("abc\ndef\n");
+}
+
 #[test]
 fn inverted_empty_pattern_short_circuits() {
     // grep short-circuits without reading stdin at all, so the harness's write