Add str reverse subcommand (#2170)

* Add str reverse subcommand

* rustfmt

crates/nu-cli/src/cli.rs

@@ -314,6 +314,7 @@ pub fn create_default_context(
             whole_stream_command(StrTrim),
             whole_stream_command(StrCollect),
             whole_stream_command(StrLength),
+            whole_stream_command(StrReverse),
             whole_stream_command(BuildString),
             whole_stream_command(Ansi),
             whole_stream_command(Char),

crates/nu-cli/src/commands.rs

@@ -252,8 +252,8 @@ pub(crate) use sort_by::SortBy;
 pub(crate) use split::{Split, SplitChars, SplitColumn, SplitRow};
 pub(crate) use split_by::SplitBy;
 pub(crate) use str_::{
-    Str, StrCapitalize, StrCollect, StrDowncase, StrFindReplace, StrFrom, StrLength, StrSet,
-    StrSubstring, StrToDatetime, StrToDecimal, StrToInteger, StrTrim, StrUpcase,
+    Str, StrCapitalize, StrCollect, StrDowncase, StrFindReplace, StrFrom, StrLength, StrReverse,
+    StrSet, StrSubstring, StrToDatetime, StrToDecimal, StrToInteger, StrTrim, StrUpcase,
 };
 #[allow(unused_imports)]
 pub(crate) use t_sort_by::TSortBy;

crates/nu-cli/src/commands/str_/mod.rs

@@ -5,6 +5,7 @@ mod downcase;
 mod find_replace;
 mod from;
 mod length;
+mod reverse;
 mod set;
 mod substring;
 mod to_datetime;
@@ -20,6 +21,7 @@ pub use downcase::SubCommand as StrDowncase;
 pub use find_replace::SubCommand as StrFindReplace;
 pub use from::SubCommand as StrFrom;
 pub use length::SubCommand as StrLength;
+pub use reverse::SubCommand as StrReverse;
 pub use set::SubCommand as StrSet;
 pub use substring::SubCommand as StrSubstring;
 pub use to_datetime::SubCommand as StrToDatetime;

crates/nu-cli/src/commands/str_/reverse.rs

@@ -0,0 +1,58 @@
+use crate::commands::WholeStreamCommand;
+use crate::prelude::*;
+use nu_errors::ShellError;
+use nu_protocol::{ReturnSuccess, Signature, UntaggedValue};
+
+pub struct SubCommand;
+
+#[async_trait]
+impl WholeStreamCommand for SubCommand {
+    fn name(&self) -> &str {
+        "str reverse"
+    }
+
+    fn signature(&self) -> Signature {
+        Signature::build("str reverse")
+    }
+
+    fn usage(&self) -> &str {
+        "outputs the reversals of the strings in the pipeline"
+    }
+
+    async fn run(
+        &self,
+        args: CommandArgs,
+        _registry: &CommandRegistry,
+    ) -> Result<OutputStream, ShellError> {
+        Ok(args
+            .input
+            .map(move |x| match x.as_string() {
+                Ok(s) => ReturnSuccess::value(
+                    UntaggedValue::string(s.chars().rev().collect::<String>())
+                        .into_untagged_value(),
+                ),
+                Err(err) => Err(err),
+            })
+            .to_output_stream())
+    }
+
+    fn examples(&self) -> Vec<Example> {
+        vec![Example {
+            description: "Return the reversals of multiple strings",
+            example: "echo 'Nushell' | str reverse",
+            result: Some(vec![UntaggedValue::string("llehsuN").into_untagged_value()]),
+        }]
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::SubCommand;
+
+    #[test]
+    fn examples_work_as_expected() {
+        use crate::examples::test as test_examples;
+
+        test_examples(SubCommand {})
+    }
+}

crates/nu-cli/tests/commands/str_.rs

@@ -404,3 +404,15 @@ fn from_table() {
     assert!(actual.out.contains("32.38"));
     assert!(actual.out.contains("15.20"));
 }
+
+#[test]
+fn str_reverse() {
+    let actual = nu!(
+        cwd: ".", pipeline(
+        r#"
+        echo "nushell" | str reverse
+        "#
+    ));
+
+    assert!(actual.out.contains("llehsun"));
+}

docs/commands/str.md

@@ -69,6 +69,11 @@ Nu
 Nu
 ```
 
+```shell
+> echo "Nushell" | str reverse
+llehsuN
+```
+
 ```shell
 > shells | str find-replace "TUX" "skipper" path
 ━━━┯━━━┯━━━━━━━━━━━━┯━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━