sort: implement -k and -t support (#1996)

* sort: implement basic -k and -t support

This allows to specify keys after the -k flag and a custom field
separator using -t.

Support for options for specific keys is still missing, and the -b flag
is not passed down correctly.

* sort: implement support for key options

* remove unstable feature use

* don't pipe in input when we expect a failure

* only tokenize when needed, remove a clone()

* improve comments

* fix clippy lints

* re-add test

* buffer writes to stdout

* fix ignore_non_printing

and make the test fail in case it is broken :)

* move attribute to the right position

* add more tests

* add my name to the copyright section

* disallow dead code

* move a comment

* re-add a loc

* use smallvec for a perf improvement in the common case

* add BENCHMARKING.md

* add ignore_case to benchmarks

tests/by-util/test_sort.rs

@@ -185,10 +185,10 @@ fn test_dictionary_order2() {
 fn test_non_printing_chars() {
     for non_printing_chars_param in vec!["-i"] {
         new_ucmd!()
-            .pipe_in("a👦🏻aa	b\naaaa	b")
+            .pipe_in("a👦🏻aa\naaaa")
             .arg(non_printing_chars_param)
             .succeeds()
-            .stdout_only("aaaa	b\na👦🏻aa	b\n");
+            .stdout_only("a👦🏻aa\naaaa\n");
     }
 }
 
@@ -307,6 +307,166 @@ fn test_numeric_unique_ints2() {
     }
 }
 
+#[test]
+fn test_keys_open_ended() {
+    let input = "aa bb cc\ndd aa ff\ngg aa cc\n";
+    new_ucmd!()
+        .args(&["-k", "2.2"])
+        .pipe_in(input)
+        .succeeds()
+        .stdout_only("gg aa cc\ndd aa ff\naa bb cc\n");
+}
+
+#[test]
+fn test_keys_closed_range() {
+    let input = "aa bb cc\ndd aa ff\ngg aa cc\n";
+    new_ucmd!()
+        .args(&["-k", "2.2,2.2"])
+        .pipe_in(input)
+        .succeeds()
+        .stdout_only("dd aa ff\ngg aa cc\naa bb cc\n");
+}
+
+#[test]
+fn test_keys_multiple_ranges() {
+    let input = "aa bb cc\ndd aa ff\ngg aa cc\n";
+    new_ucmd!()
+        .args(&["-k", "2,2", "-k", "3,3"])
+        .pipe_in(input)
+        .succeeds()
+        .stdout_only("gg aa cc\ndd aa ff\naa bb cc\n");
+}
+
+#[test]
+fn test_keys_no_field_match() {
+    let input = "aa aa aa aa\naa bb cc\ndd aa ff\n";
+    new_ucmd!()
+        .args(&["-k", "4,4"])
+        .pipe_in(input)
+        .succeeds()
+        .stdout_only("aa bb cc\ndd aa ff\naa aa aa aa\n");
+}
+
+#[test]
+fn test_keys_no_char_match() {
+    let input = "aaa\nba\nc\n";
+    new_ucmd!()
+        .args(&["-k", "1.2"])
+        .pipe_in(input)
+        .succeeds()
+        .stdout_only("c\nba\naaa\n");
+}
+
+#[test]
+fn test_keys_custom_separator() {
+    let input = "aaxbbxcc\nddxaaxff\nggxaaxcc\n";
+    new_ucmd!()
+        .args(&["-k", "2.2,2.2", "-t", "x"])
+        .pipe_in(input)
+        .succeeds()
+        .stdout_only("ddxaaxff\nggxaaxcc\naaxbbxcc\n");
+}
+
+#[test]
+fn test_keys_invalid_field() {
+    new_ucmd!()
+        .args(&["-k", "1."])
+        .fails()
+        .stderr_only("sort: error: failed to parse character index for key `1.`: cannot parse integer from empty string");
+}
+
+#[test]
+fn test_keys_invalid_field_option() {
+    new_ucmd!()
+        .args(&["-k", "1.1x"])
+        .fails()
+        .stderr_only("sort: error: invalid option for key: `x`");
+}
+
+#[test]
+fn test_keys_invalid_field_zero() {
+    new_ucmd!()
+        .args(&["-k", "0.1"])
+        .fails()
+        .stderr_only("sort: error: field index was 0");
+}
+
+#[test]
+fn test_keys_with_options() {
+    let input = "aa 3 cc\ndd 1 ff\ngg 2 cc\n";
+    for param in &[
+        &["-k", "2,2n"][..],
+        &["-k", "2n,2"][..],
+        &["-k", "2,2", "-n"][..],
+    ] {
+        new_ucmd!()
+            .args(param)
+            .pipe_in(input)
+            .succeeds()
+            .stdout_only("dd 1 ff\ngg 2 cc\naa 3 cc\n");
+    }
+}
+
+#[test]
+fn test_keys_with_options_blanks_start() {
+    let input = "aa   3 cc\ndd  1 ff\ngg         2 cc\n";
+    for param in &[&["-k", "2b,2"][..], &["-k", "2,2", "-b"][..]] {
+        new_ucmd!()
+            .args(param)
+            .pipe_in(input)
+            .succeeds()
+            .stdout_only("dd  1 ff\ngg         2 cc\naa   3 cc\n");
+    }
+}
+
+#[test]
+fn test_keys_with_options_blanks_end() {
+    let input = "a  b
+a b
+a   b
+";
+    new_ucmd!()
+        .args(&["-k", "1,2.1b", "-s"])
+        .pipe_in(input)
+        .succeeds()
+        .stdout_only(
+            "a   b
+a  b
+a b
+",
+        );
+}
+
+#[test]
+fn test_keys_stable() {
+    let input = "a  b
+a b
+a   b
+";
+    new_ucmd!()
+        .args(&["-k", "1,2.1", "-s"])
+        .pipe_in(input)
+        .succeeds()
+        .stdout_only(
+            "a  b
+a b
+a   b
+",
+        );
+}
+
+#[test]
+fn test_keys_empty_match() {
+    let input = "a a a a
+aaaa
+";
+    new_ucmd!()
+        .args(&["-k", "1,1", "-t", "a"])
+        .pipe_in(input)
+        .succeeds()
+        .stdout_only(input);
+}
+
 #[test]
 fn test_zero_terminated() {
     test_helper("zero-terminated", "-z");