diff: add -N and --unidirectional-new-file

Author: sylvestre

src/diff.rs

@@ -3,7 +3,7 @@
 // For the full copyright and license information, please view the LICENSE-*
 // files that was distributed with this source code.
 
-use crate::params::{parse_params, Format};
+use crate::params::{parse_params, Format, MissingFile};
 use crate::utils::report_failure_to_read_input_file;
 use crate::{context_diff, ed_diff, normal_diff, side_diff, unified_diff};
 use std::env::ArgsOs;
@@ -52,6 +52,11 @@ pub fn main(opts: Peekable<ArgsOs>) -> ExitCode {
     let mut io_error = false;
     let from_content = match read_file_contents(&params.from) {
         Ok(from_content) => from_content,
+        Err(e)
+            if e.kind() == io::ErrorKind::NotFound && params.missing_file != MissingFile::Error =>
+        {
+            vec![]
+        }
         Err(e) => {
             report_failure_to_read_input_file(&params.executable, &params.from, &e);
             io_error = true;
@@ -60,6 +65,11 @@ pub fn main(opts: Peekable<ArgsOs>) -> ExitCode {
     };
     let to_content = match read_file_contents(&params.to) {
         Ok(to_content) => to_content,
+        Err(e)
+            if e.kind() == io::ErrorKind::NotFound && params.missing_file == MissingFile::Empty =>
+        {
+            vec![]
+        }
         Err(e) => {
             report_failure_to_read_input_file(&params.executable, &params.to, &e);
             io_error = true;

src/params.rs

@@ -14,6 +14,19 @@ pub enum Format {
     SideBySide,
 }
 
+/// How to handle an operand that does not exist (`-N` and
+/// `--unidirectional-new-file`).
+#[derive(Clone, Copy, Debug, Default, Eq, PartialEq)]
+pub enum MissingFile {
+    /// A missing operand is an error.
+    #[default]
+    Error,
+    /// A missing operand is treated as an empty file.
+    Empty,
+    /// Only a missing first operand is treated as an empty file.
+    EmptyIfFirst,
+}
+
 #[derive(Clone, Debug, Eq, PartialEq)]
 pub struct Params {
     pub executable: OsString,
@@ -26,6 +39,7 @@ pub struct Params {
     pub expand_tabs: bool,
     pub tabsize: usize,
     pub width: usize,
+    pub missing_file: MissingFile,
 }
 
 impl Default for Params {
@@ -41,6 +55,7 @@ impl Default for Params {
             expand_tabs: false,
             tabsize: 8,
             width: 130,
+            missing_file: MissingFile::default(),
         }
     }
 }
@@ -87,6 +102,16 @@ pub fn parse_params<I: Iterator<Item = OsString>>(mut opts: Peekable<I>) -> Resu
             params.brief = true;
             continue;
         }
+        if param == "-N" || param == "--new-file" {
+            params.missing_file = MissingFile::Empty;
+            continue;
+        }
+        if param == "--unidirectional-new-file" {
+            if params.missing_file != MissingFile::Empty {
+                params.missing_file = MissingFile::EmptyIfFirst;
+            }
+            continue;
+        }
         if param == "-t" || param == "--expand-tabs" {
             params.expand_tabs = true;
             continue;

tests/by-util/test_diff.rs

@@ -206,6 +206,44 @@ fn read_from_stdin() -> Result<(), Box<dyn std::error::Error>> {
     Ok(())
 }
 
+#[test]
+fn missing_file_as_empty() -> Result<(), Box<dyn std::error::Error>> {
+    let tmp_dir = tempdir()?;
+    let present = tmp_dir.path().join("present");
+    let absent = tmp_dir.path().join("absent");
+    std::fs::write(&present, "kiwi\nmango\n")?;
+
+    for option in ["-N", "--new-file", "--unidirectional-new-file"] {
+        let mut cmd = cargo_bin_cmd!("diffutils");
+        cmd.arg("diff").arg(option).arg(&absent).arg(&present);
+        cmd.assert()
+            .code(predicate::eq(1))
+            .failure()
+            .stdout("0a1,2\n> kiwi\n> mango\n");
+    }
+
+    let mut cmd = cargo_bin_cmd!("diffutils");
+    cmd.arg("diff").arg("-N").arg(&present).arg(&absent);
+    cmd.assert()
+        .code(predicate::eq(1))
+        .failure()
+        .stdout("1,2d0\n< kiwi\n< mango\n");
+
+    // Only a missing first operand is accepted here.
+    let mut cmd = cargo_bin_cmd!("diffutils");
+    cmd.arg("diff")
+        .arg("--unidirectional-new-file")
+        .arg(&present)
+        .arg(&absent);
+    cmd.assert().code(predicate::eq(2)).failure();
+
+    // Without the option, a missing file is trouble.
+    let mut cmd = cargo_bin_cmd!("diffutils");
+    cmd.arg("diff").arg(&absent).arg(&present);
+    cmd.assert().code(predicate::eq(2)).failure();
+    Ok(())
+}
+
 #[test]
 fn compare_file_to_directory() -> Result<(), Box<dyn std::error::Error>> {
     let tmp_dir = tempdir()?;