output: add --stats flag

This commit provides basic support for a --stats flag, which will print
various aggregate statistics about a search after all of the results
have been printed. This is mostly intended to support a similar feature
found in the Silver Searcher. Note though that we don't emit the total
bytes searched; this is a first pass at an implementation and we can
improve upon it later.

Closes #411, Closes #799

src/main.rs

@@ -27,6 +27,7 @@ use std::sync::Arc;
 use std::sync::atomic::{AtomicUsize, Ordering};
 use std::sync::mpsc;
 use std::thread;
+use std::time::{Duration, Instant};
 
 use args::Args;
 use worker::Work;
@@ -85,16 +86,19 @@ fn run(args: Arc<Args>) -> Result<u64> {
 }
 
 fn run_parallel(args: &Arc<Args>) -> Result<u64> {
+    let start_time = Instant::now();
     let bufwtr = Arc::new(args.buffer_writer());
     let quiet_matched = args.quiet_matched();
     let paths_searched = Arc::new(AtomicUsize::new(0));
     let match_line_count = Arc::new(AtomicUsize::new(0));
+    let paths_matched = Arc::new(AtomicUsize::new(0));
 
     args.walker_parallel().run(|| {
         let args = Arc::clone(args);
         let quiet_matched = quiet_matched.clone();
         let paths_searched = paths_searched.clone();
         let match_line_count = match_line_count.clone();
+        let paths_matched = paths_matched.clone();
         let bufwtr = Arc::clone(&bufwtr);
         let mut buf = bufwtr.buffer();
         let mut worker = args.worker();
@@ -129,6 +133,9 @@ fn run_parallel(args: &Arc<Args>) -> Result<u64> {
                 if quiet_matched.set_match(count > 0) {
                     return Quit;
                 }
+                if args.stats() && count > 0 {
+                    paths_matched.fetch_add(1, Ordering::SeqCst);
+                }
             }
             // BUG(burntsushi): We should handle this error instead of ignoring
             // it. See: https://github.com/BurntSushi/ripgrep/issues/200
@@ -141,15 +148,28 @@ fn run_parallel(args: &Arc<Args>) -> Result<u64> {
             eprint_nothing_searched();
         }
     }
-    Ok(match_line_count.load(Ordering::SeqCst) as u64)
+    let match_line_count = match_line_count.load(Ordering::SeqCst) as u64;
+    let paths_searched = paths_searched.load(Ordering::SeqCst) as u64;
+    let paths_matched = paths_matched.load(Ordering::SeqCst) as u64;
+    if args.stats() {
+        print_stats(
+            match_line_count,
+            paths_searched,
+            paths_matched,
+            start_time.elapsed(),
+        );
+    }
+    Ok(match_line_count)
 }
 
 fn run_one_thread(args: &Arc<Args>) -> Result<u64> {
+    let start_time = Instant::now();
     let stdout = args.stdout();
     let mut stdout = stdout.lock();
     let mut worker = args.worker();
     let mut paths_searched: u64 = 0;
     let mut match_line_count = 0;
+    let mut paths_matched: u64 = 0;
     for result in args.walker() {
         let dent = match get_or_log_dir_entry(
             result,
@@ -170,18 +190,30 @@ fn run_one_thread(args: &Arc<Args>) -> Result<u64> {
             }
         }
         paths_searched += 1;
-        match_line_count +=
+        let count =
             if dent.is_stdin() {
                 worker.run(&mut printer, Work::Stdin)
             } else {
                 worker.run(&mut printer, Work::DirEntry(dent))
             };
+        match_line_count += count;
+        if args.stats() && count > 0 {
+            paths_matched += 1;
+        }
     }
     if !args.paths().is_empty() && paths_searched == 0 {
         if !args.no_messages() {
             eprint_nothing_searched();
         }
     }
+    if args.stats() {
+        print_stats(
+            match_line_count,
+            paths_searched,
+            paths_matched,
+            start_time.elapsed(),
+        );
+    }
     Ok(match_line_count)
 }
 
@@ -373,6 +405,22 @@ fn eprint_nothing_searched() {
                Try running again with --debug.");
 }
 
+fn print_stats(
+    match_count: u64,
+    paths_searched: u64,
+    paths_matched: u64,
+    time_elapsed: Duration,
+) {
+    let time_elapsed =
+        time_elapsed.as_secs() as f64
+        + (time_elapsed.subsec_nanos() as f64 * 1e-9);
+    println!("\n{} matched lines\n\
+              {} files contained matches\n\
+              {} files searched\n\
+              {:.3} seconds", match_count, paths_matched,
+             paths_searched, time_elapsed);
+}
+
 // The Rust standard library suppresses the default SIGPIPE behavior, so that
 // writing to a closed pipe doesn't kill the process. The goal is to instead
 // handle errors through the normal result mechanism. Ripgrep needs some