cli: change --no-captures to --captures (all|implicit|none)

When we added the WhichCaptures type, we didn't update the CLI to expose
the full functionality. This change does that.

regex-automata/src/nfa/thompson/map.rs

@@ -65,7 +65,7 @@ const INIT: u64 = 14695981039346656037;
 /// Specifically, one could observe the difference with std's hashmap via
 /// something like the following benchmark:
 ///
-///   hyperfine "regex-cli debug thompson -qr --no-captures '\w{90} ecurB'"
+///   hyperfine "regex-cli debug thompson -qr --captures none '\w{90} ecurB'"
 ///
 /// But to observe that difference, you'd have to modify the code to use
 /// std's hashmap.

regex-automata/src/nfa/thompson/range_trie.rs

@@ -594,7 +594,7 @@ impl State {
         // Benchmarks suggest that binary search is just a bit faster than
         // straight linear search. Specifically when using the debug tool:
         //
-        //   hyperfine "regex-cli debug thompson -qr --no-captures '\w{90} ecurB'"
+        //   hyperfine "regex-cli debug thompson -qr --captures none '\w{90} ecurB'"
         binary_search(&self.transitions, |t| range.start <= t.range.end)
     }
 

regex-cli/args/flags.rs

@@ -152,3 +152,55 @@ impl std::str::FromStr for MatchKind {
         Ok(MatchKind { kind })
     }
 }
+
+/// Provides an implementation of the --captures flag, for use with Thompson
+/// NFA configuration.
+#[derive(Debug)]
+pub struct WhichCaptures {
+    pub which: regex_automata::nfa::thompson::WhichCaptures,
+}
+
+impl WhichCaptures {
+    pub const USAGE: Usage = Usage::new(
+        "--captures <which>",
+        "One of: all, implicit or none.",
+        r#"
+Selects which capture states should be included in the Thompson NFA. The
+choices are 'all' (the default), 'implicit' or 'none'.
+
+'all' means that both explicit and implicit capture states are included.
+
+'implicit' means that only implicit capture states are included. That is, the
+Thompson NFA will only be able to report the overall match offsets and not the
+match offsets of each explicit capture group.
+
+'none' means that no capture states will be included. This is useful when
+capture states aren't needed (like when building a DFA) or if they aren't
+supported (like when building a reverse NFA).
+"#,
+    );
+}
+
+impl Default for WhichCaptures {
+    fn default() -> WhichCaptures {
+        WhichCaptures {
+            which: regex_automata::nfa::thompson::WhichCaptures::All,
+        }
+    }
+}
+
+impl std::str::FromStr for WhichCaptures {
+    type Err = anyhow::Error;
+
+    fn from_str(s: &str) -> anyhow::Result<WhichCaptures> {
+        let which = match s {
+            "all" => regex_automata::nfa::thompson::WhichCaptures::All,
+            "implicit" => {
+                regex_automata::nfa::thompson::WhichCaptures::Implicit
+            }
+            "none" => regex_automata::nfa::thompson::WhichCaptures::None,
+            unk => anyhow::bail!("unrecognized captures option '{}'", unk),
+        };
+        Ok(WhichCaptures { which })
+    }
+}

regex-cli/args/thompson.rs

@@ -70,11 +70,11 @@ impl Configurable for Config {
             Arg::Long("shrink") => {
                 self.thompson = self.thompson.clone().shrink(true);
             }
-            Arg::Long("no-captures") => {
-                self.thompson = self
-                    .thompson
-                    .clone()
-                    .which_captures(thompson::WhichCaptures::None);
+            Arg::Long("captures") => {
+                let which: flags::WhichCaptures =
+                    args::parse(p, "--captures")?;
+                self.thompson =
+                    self.thompson.clone().which_captures(which.which);
             }
             Arg::Long("line-terminator") => {
                 let byte: flags::OneByte =
@@ -136,19 +136,7 @@ spent shrinking the NFA can lead to far larger savings in the subsequent DFA
 determinization.
 "#,
             ),
-            Usage::new(
-                "--no-captures",
-                "Disable capture states.",
-                r#"
-Disables capture states. By default, NFAs include special "capture" states that
-instruct some regex engines (like the PikeVM) to record offset positions in
-ancillary state.
-
-It can be useful to disable capture states in order to reduce "clutter" in the
-automaton when debugging it. Also, at time of writing, reverse NFAs require
-that capture groups are disabled.
-"#,
-            ),
+            flags::WhichCaptures::USAGE,
             Usage::new(
                 "--line-terminator",
                 "Set the line terminator used by line anchors.",