delta acts as `diff -u minus_file plus_file | delta` when there is no stdin

3 files changed, 59 insertions, 0 deletions

diff --git a/src/cli.rs b/src/cli.rs
index c22ebe24..b06743aa 100644
--- a/src/cli.rs
+++ b/src/cli.rs
@@ -1,3 +1,4 @@
+use std::path::PathBuf;
 use std::process;
 
 use structopt::clap::AppSettings::{ColorAlways, ColoredHelp, DeriveDisplayOrder};
@@ -287,6 +288,14 @@ pub struct Opt {
     #[structopt(long = "paging", default_value = "auto")]
     pub paging_mode: String,
 
+    /// First file to be compared when delta is being used in diff mode.
+    #[structopt(parse(from_os_str))]
+    pub minus_file: Option<PathBuf>,
+
+    /// Second file to be compared when delta is being used in diff mode.
+    #[structopt(parse(from_os_str))]
+    pub plus_file: Option<PathBuf>,
+
     #[structopt(long = "minus-color")]
     /// Deprecated: use --minus-style='normal my_background_color'.
     pub deprecated_minus_background_color: Option<String>,
diff --git a/src/config.rs b/src/config.rs
index e96dca41..1005a782 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -1,4 +1,5 @@
 use std::cmp::min;
+use std::path::PathBuf;
 use std::process;
 
 use console::Term;
@@ -51,6 +52,8 @@ pub struct Config<'a> {
     pub null_syntect_style: SyntectStyle,
     pub max_buffered_lines: usize,
     pub paging_mode: PagingMode,
+    pub minus_file: Option<PathBuf>,
+    pub plus_file: Option<PathBuf>,
 }
 
 impl<'a> Config<'a> {
@@ -172,6 +175,8 @@ pub fn get_config<'a>(
         null_syntect_style: SyntectStyle::default(),
         max_buffered_lines: 32,
         paging_mode,
+        minus_file: opt.minus_file,
+        plus_file: opt.plus_file,
     }
 }
 
diff --git a/src/main.rs b/src/main.rs
index 2f92f498..c5944daa 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -21,6 +21,8 @@ mod tests;
 mod theme;
 
 use std::io::{self, ErrorKind, Read, Write};
+use std::os::unix::process::CommandExt;
+use std::path::PathBuf;
 use std::process;
 
 use ansi_term::{self, Color};
@@ -61,6 +63,11 @@ fn main() -> std::io::Result<()> {
 
     let config = cli::process_command_line_arguments(opt, Some(arg_matches));
 
+    if atty::is(atty::Stream::Stdin) {
+        delta_diff(config);
+        process::exit(0);
+    }
+
     if show_background_colors_option {
         show_background_colors(&config);
         process::exit(0);
@@ -78,6 +85,44 @@ fn main() -> std::io::Result<()> {
     Ok(())
 }
 
+fn delta_diff(config: config::Config) {
+    let mut output_type = OutputType::from_mode(config.paging_mode, None, &config).unwrap();
+    let writer = output_type.handle().unwrap();
+    let die = || {
+        eprintln!("Usage: delta minus_file plus_file");
+        process::exit(1);
+    };
+    let minus_file = config.minus_file.unwrap_or_else(die);
+    let plus_file = config.plus_file.unwrap_or_else(die);
+
+    let diff_process = process::Command::new(PathBuf::from("diff"))
+        .arg("-u")
+        .args(&[minus_file, plus_file])
+        .stdout(process::Stdio::piped())
+        .spawn()
+        .unwrap();
+
+    if cfg!(unix) {
+        process::Command::new(PathBuf::from("delta"))
+            .stdin(diff_process.stdout.unwrap())
+            .exec();
+    } else {
+        // TODO: Send stdout of child delta process directly to less.
+        let mut buf = String::new();
+        process::Command::new(PathBuf::from("delta"))
+            .stdin(diff_process.stdout.unwrap())
+            .stdout(process::Stdio::piped())
+            .spawn()
+            .unwrap()
+            .stdout
+            .unwrap()
+            .read_to_string(&mut buf)
+            .unwrap();
+        write!(writer, "{}", buf).unwrap();
+        process::exit(0);
+    }
+}
+
 fn show_background_colors(config: &config::Config) {
     println!(
         "delta \