sort --merge --unique

This uses Itertools' dedup() rather than Vec::dedup(). There is probably
a cleaner, more polymorphic way to do this. Suggestions welcome.

src/sort/Cargo.toml

@@ -11,6 +11,7 @@ path = "sort.rs"
 getopts = "*"
 libc = "*"
 semver = "*"
+itertools = "*"
 uucore = { path="../uucore" }
 
 [[bin]]

src/sort/sort.rs

@@ -17,6 +17,8 @@ extern crate semver;
 
 #[macro_use]
 extern crate uucore;
+#[macro_use]
+extern crate itertools;
 
 use std::cmp::Ordering;
 use std::collections::BinaryHeap;
@@ -26,6 +28,7 @@ use std::mem::replace;
 use std::path::Path;
 use uucore::fs::is_stdin_interactive;
 use semver::Version;
+use itertools::Itertools; // for Iterator::dedup()
 
 static NAME: &'static str = "sort";
 static VERSION: &'static str = env!("CARGO_PKG_VERSION");
@@ -261,10 +264,6 @@ fn exec(files: Vec<String>, settings: &Settings) -> i32 {
 
     sort_by(&mut lines, &settings);
 
-    if settings.unique {
-        lines.dedup()
-    }
-
     if settings.check {
         for (i, line) in lines.iter().enumerate() {
             if line != &original_lines[i] {
@@ -274,10 +273,20 @@ fn exec(files: Vec<String>, settings: &Settings) -> i32 {
         }
     }
     else if settings.merge {
-        print_sorted(file_merger, &settings.outfile)
+        if settings.unique {
+            print_sorted(file_merger.dedup(), &settings.outfile)
+        }
+        else {
+            print_sorted(file_merger, &settings.outfile)
+        }
     }
     else {
-        print_sorted(lines.iter(), &settings.outfile)
+        if settings.unique {
+            print_sorted(lines.iter().dedup(), &settings.outfile)
+        }
+        else {
+            print_sorted(lines.iter(), &settings.outfile)
+        }
     }
 
     0

tests/test_sort.rs

@@ -80,6 +80,20 @@ fn test_merge_interleaved() {
         .succeeds().stdout_is_fixture("merge_ints_interleaved.expected");
 }
 
+#[test]
+fn test_merge_unique() {
+    new_ucmd()
+        .arg("-m")
+        .arg("--unique")
+        .arg("merge_ints_interleaved_1.txt")
+        .arg("merge_ints_interleaved_2.txt")
+        .arg("merge_ints_interleaved_3.txt")
+        .arg("merge_ints_interleaved_3.txt")
+        .arg("merge_ints_interleaved_2.txt")
+        .arg("merge_ints_interleaved_1.txt")
+        .succeeds().stdout_is_fixture("merge_ints_interleaved.expected");
+}
+
 #[test]
 fn test_merge_reversed() {
     new_ucmd()