1 files changed, 92 insertions, 0 deletions
diff --git a/third_party/rust/clap_builder/src/output/textwrap/word_separators.rs b/third_party/rust/clap_builder/src/output/textwrap/word_separators.rs
new file mode 100644
index 0000000000..cb8250b601
--- /dev/null
+++ b/third_party/rust/clap_builder/src/output/textwrap/word_separators.rs
@@ -0,0 +1,92 @@
+pub(crate) fn find_words_ascii_space(line: &str) -> impl Iterator<Item = &'_ str> + '_ {
+    let mut start = 0;
+    let mut in_whitespace = false;
+    let mut char_indices = line.char_indices();
+
+    std::iter::from_fn(move || {
+        for (idx, ch) in char_indices.by_ref() {
+            let next_whitespace = ch == ' ';
+            if in_whitespace && !next_whitespace {
+                let word = &line[start..idx];
+                start = idx;
+                in_whitespace = next_whitespace;
+                return Some(word);
+            }
+
+            in_whitespace = next_whitespace;
+        }
+
+        if start < line.len() {
+            let word = &line[start..];
+            start = line.len();
+            return Some(word);
+        }
+
+        None
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    macro_rules! test_find_words {
+        ($ascii_name:ident,
+         $([ $line:expr, $ascii_words:expr ]),+) => {
+            #[test]
+            fn $ascii_name() {
+                $(
+                    let expected_words: Vec<&str> = $ascii_words.to_vec();
+                    let actual_words = find_words_ascii_space($line)
+                        .collect::<Vec<_>>();
+                    assert_eq!(actual_words, expected_words, "Line: {:?}", $line);
+                )+
+            }
+        };
+    }
+
+    test_find_words!(ascii_space_empty, ["", []]);
+
+    test_find_words!(ascii_single_word, ["foo", ["foo"]]);
+
+    test_find_words!(ascii_two_words, ["foo bar", ["foo ", "bar"]]);
+
+    test_find_words!(
+        ascii_multiple_words,
+        ["foo bar", ["foo ", "bar"]],
+        ["x y z", ["x ", "y ", "z"]]
+    );
+
+    test_find_words!(ascii_only_whitespace, [" ", [" "]], ["    ", ["    "]]);
+
+    test_find_words!(
+        ascii_inter_word_whitespace,
+        ["foo   bar", ["foo   ", "bar"]]
+    );
+
+    test_find_words!(ascii_trailing_whitespace, ["foo   ", ["foo   "]]);
+
+    test_find_words!(ascii_leading_whitespace, ["   foo", ["   ", "foo"]]);
+
+    test_find_words!(
+        ascii_multi_column_char,
+        ["\u{1f920}", ["\u{1f920}"]] // cowboy emoji 🤠
+    );
+
+    test_find_words!(
+        ascii_hyphens,
+        ["foo-bar", ["foo-bar"]],
+        ["foo- bar", ["foo- ", "bar"]],
+        ["foo - bar", ["foo ", "- ", "bar"]],
+        ["foo -bar", ["foo ", "-bar"]]
+    );
+
+    test_find_words!(ascii_newline, ["foo\nbar", ["foo\nbar"]]);
+
+    test_find_words!(ascii_tab, ["foo\tbar", ["foo\tbar"]]);
+
+    test_find_words!(
+        ascii_non_breaking_space,
+        ["foo\u{00A0}bar", ["foo\u{00A0}bar"]]
+    );
+}