Don't search stdout redirected file.

When running ripgrep like this:

    rg foo > output

we must be careful not to search `output` since ripgrep is actively writing
to it. Searching it can cause massive blowups where the file grows without
bound.

While this is conceptually easy to fix (check the inode of the redirection
and the inode of the file you're about to search), there are a few problems
with it.

First, inodes are a Unix thing, so we need a Windows specific solution to
this as well. To resolve this concern, I created a new crate, `same-file`,
which provides a cross platform abstraction.

Second, stat'ing every file is costly. This is not avoidable on Windows,
but on Unix, we can get the inode number directly from directory traversal.
However, this information wasn't exposed, but now it is (through both the
ignore and walkdir crates).

Fixes #286

1 files changed, 70 insertions, 10 deletions

diff --git a/src/main.rs b/src/main.rs
index 236c093e..735298f9 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -15,6 +15,7 @@ extern crate memchr;
 extern crate memmap;
 extern crate num_cpus;
 extern crate regex;
+extern crate same_file;
 extern crate termcolor;
 #[cfg(windows)]
 extern crate winapi;
@@ -106,7 +107,11 @@ fn run_parallel(args: Arc<Args>) -> Result<u64> {
             if quiet_matched.has_match() {
                 return Quit;
             }
-            let dent = match get_or_log_dir_entry(result, args.no_messages()) {
+            let dent = match get_or_log_dir_entry(
+                result,
+                args.stdout_handle(),
+                args.no_messages(),
+            ) {
                 None => return Continue,
                 Some(dent) => dent,
             };
@@ -148,7 +153,11 @@ fn run_one_thread(args: Arc<Args>) -> Result<u64> {
     let mut paths_searched: u64 = 0;
     let mut match_count = 0;
     for result in args.walker() {
-        let dent = match get_or_log_dir_entry(result, args.no_messages()) {
+        let dent = match get_or_log_dir_entry(
+            result,
+            args.stdout_handle(),
+            args.no_messages(),
+        ) {
             None => continue,
             Some(dent) => dent,
         };
@@ -190,11 +199,15 @@ fn run_files_parallel(args: Arc<Args>) -> Result<u64> {
         }
         file_count
     });
-    let no_messages = args.no_messages();
     args.walker_parallel().run(move || {
+        let args = args.clone();
         let tx = tx.clone();
         Box::new(move |result| {
-            if let Some(dent) = get_or_log_dir_entry(result, no_messages) {
+            if let Some(dent) = get_or_log_dir_entry(
+                result,
+                args.stdout_handle(),
+                args.no_messages(),
+            ) {
                 tx.send(dent).unwrap();
             }
             ignore::WalkState::Continue
@@ -208,7 +221,11 @@ fn run_files_one_thread(args: Arc<Args>) -> Result<u64> {
     let mut printer = args.printer(stdout.lock());
     let mut file_count = 0;
     for result in args.walker() {
-        let dent = match get_or_log_dir_entry(result, args.no_messages()) {
+        let dent = match get_or_log_dir_entry(
+            result,
+            args.stdout_handle(),
+            args.no_messages(),
+        ) {
             None => continue,
             Some(dent) => dent,
         };
@@ -231,6 +248,7 @@ fn run_types(args: Arc<Args>) -> Result<u64> {
 
 fn get_or_log_dir_entry(
     result: result::Result<ignore::DirEntry, ignore::Error>,
+    stdout_handle: Option<&same_file::Handle>,
     no_messages: bool,
 ) -> Option<ignore::DirEntry> {
     match result {
@@ -253,16 +271,58 @@ fn get_or_log_dir_entry(
             // A depth of 0 means the user gave the path explicitly, so we
             // should always try to search it.
             if dent.depth() == 0 && !ft.is_dir() {
-                Some(dent)
-            } else if ft.is_file() {
-                Some(dent)
-            } else {
-                None
+                return Some(dent);
+            } else if !ft.is_file() {
+                return None;
+            }
+            // If we are redirecting stdout to a file, then don't search that
+            // file.
+            if is_stdout_file(&dent, stdout_handle, no_messages) {
+                return None;
+            }
+            Some(dent)
+        }
+    }
+}
+
+fn is_stdout_file(
+    dent: &ignore::DirEntry,
+    stdout_handle: Option<&same_file::Handle>,
+    no_messages: bool,
+) -> bool {
+    let stdout_handle = match stdout_handle {
+        None => return false,
+        Some(stdout_handle) => stdout_handle,
+    };
+    // If we know for sure that these two things aren't equal, then avoid
+    // the costly extra stat call to determine equality.
+    if !maybe_dent_eq_handle(dent, stdout_handle) {
+        return false;
+    }
+    match same_file::Handle::from_path(dent.path()) {
+        Ok(h) => stdout_handle == &h,
+        Err(err) => {
+            if !no_messages {
+                eprintln!("{}: {}", dent.path().display(), err);
             }
+            false
         }
     }
 }
 
+#[cfg(unix)]
+fn maybe_dent_eq_handle(
+    dent: &ignore::DirEntry,
+    handle: &same_file::Handle,
+) -> bool {
+    dent.ino() == Some(handle.ino())
+}
+
+#[cfg(not(unix))]
+fn maybe_dent_eq_handle(_: &ignore::DirEntry, _: &same_file::Handle) -> bool {
+    true
+}
+
 fn eprint_nothing_searched() {
     eprintln!("No files were searched, which means ripgrep probably \
                applied a filter you didn't expect. \