Detect infinite loop when input and output are the same

Cargo.toml

@@ -51,6 +51,7 @@ serde = { version = "1.0", features = ["derive"] }
 serde_yaml = "0.8"
 semver = "0.11"
 path_abs = { version = "0.5", default-features = false }
+clircle = "0.1.3"
 
 [dependencies.git2]
 version = "0.13"

src/controller.rs

@@ -13,6 +13,7 @@ use crate::output::OutputType;
 #[cfg(feature = "paging")]
 use crate::paging::PagingMode;
 use crate::printer::{InteractivePrinter, Printer, SimplePrinter};
+use std::convert::TryFrom;
 
 pub struct Controller<'a> {
     config: &'a Config<'a>,
@@ -66,6 +67,14 @@ impl<'b> Controller<'b> {
         }
 
         let attached_to_pager = output_type.is_pager();
+        let rw_cycle_detected = !attached_to_pager && {
+            let identifiers: Vec<_> = inputs
+                .iter()
+                .flat_map(clircle::Identifier::try_from)
+                .collect();
+            clircle::stdout_among_inputs(&identifiers)
+        };
+
         let writer = output_type.handle()?;
         let mut no_errors: bool = true;
 
@@ -78,6 +87,11 @@ impl<'b> Controller<'b> {
             }
         };
 
+        if rw_cycle_detected {
+            print_error(&"The output file is also an input!".into(), writer);
+            return Ok(false);
+        }
+
         for (index, input) in inputs.into_iter().enumerate() {
             match input.open(io::stdin().lock()) {
                 Err(error) => {

src/input.rs

@@ -1,6 +1,8 @@
+use std::convert::TryFrom;
 use std::ffi::{OsStr, OsString};
 use std::fs::File;
 use std::io::{self, BufRead, BufReader, Read};
+use std::path::Path;
 
 use content_inspector::{self, ContentType};
 
@@ -192,6 +194,18 @@ impl<'a> Input<'a> {
     }
 }
 
+impl TryFrom<&'_ Input<'_>> for clircle::Identifier {
+    type Error = ();
+
+    fn try_from(input: &Input) -> std::result::Result<clircle::Identifier, ()> {
+        match input.kind {
+            InputKind::OrdinaryFile(ref path) => Self::try_from(Path::new(path)).map_err(|_| ()),
+            InputKind::StdIn => Self::try_from(clircle::Stdio::Stdin).map_err(|_| ()),
+            InputKind::CustomReader(_) => Err(()),
+        }
+    }
+}
+
 pub(crate) struct InputReader<'a> {
     inner: Box<dyn BufRead + 'a>,
     pub(crate) first_line: Vec<u8>,

tests/integration_tests.rs

@@ -1,11 +1,14 @@
-use assert_cmd::Command;
+use assert_cmd::assert::OutputAssertExt;
+use assert_cmd::cargo::CommandCargoExt;
 use predicates::{prelude::predicate, str::PredicateStrExt};
+use std::fs::File;
 use std::path::Path;
+use std::process::{Command, Stdio};
 use std::str::from_utf8;
 
 const EXAMPLES_DIR: &str = "tests/examples";
 
-fn bat_with_config() -> Command {
+fn bat_as_std() -> Command {
     let mut cmd = Command::cargo_bin("bat").unwrap();
     cmd.current_dir("tests/examples");
     cmd.env_remove("PAGER");
@@ -17,7 +20,11 @@ fn bat_with_config() -> Command {
     cmd
 }
 
-fn bat() -> Command {
+fn bat_with_config() -> assert_cmd::Command {
+    assert_cmd::Command::from_std(bat_as_std())
+}
+
+fn bat() -> assert_cmd::Command {
     let mut cmd = bat_with_config();
     cmd.arg("--no-config");
     cmd
@@ -189,6 +196,30 @@ fn line_range_multiple() {
         .stdout("line 1\nline 2\nline 4\n");
 }
 
+#[test]
+fn basic_io_cycle() {
+    let file_out = Stdio::from(File::open("tests/examples/cycle.txt").unwrap());
+    bat_as_std()
+        .arg("test.txt")
+        .arg("cycle.txt")
+        .stdout(file_out)
+        .assert()
+        .failure();
+}
+
+#[test]
+fn stdin_to_stdout_cycle() {
+    let file_out = Stdio::from(File::open("tests/examples/cycle.txt").unwrap());
+    let file_in = Stdio::from(File::open("tests/examples/cycle.txt").unwrap());
+    bat_as_std()
+        .stdin(file_in)
+        .arg("test.txt")
+        .arg("-")
+        .stdout(file_out)
+        .assert()
+        .failure();
+}
+
 #[test]
 fn tabs_numbers() {
     bat()