implement whoami using uutils (nushell#10488)

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# Description
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Implements `whoami` using the `whoami` command from uutils as backend.
This is a draft because it depends on
uutils/coreutils#5310 and a new release of
uutils needs to be made (and the paths in `Cargo.toml` should be
updated). At this point, this is more of a proof of concept 😄

Additionally, this implements a (simple and naive) conversion from the
uutils `UResult` to the nushell `ShellError`, which should help with the
integration of other utils, too. I can split that off into a separate PR
if desired.

I put this command in the "platform" category. If it should go somewhere
else, let me know!

The tests will currently fail, because I've used a local path to uutils.
Once the PR on the uutils side is merged, I'll update it to a git path
so that it can be tested and runs on more machines than just mine.

# User-Facing Changes
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New `whoami` command. This might break some users who expect the system
`whoami` command. However, the result of this new command should be very
close, just with a nicer help message, at least for Linux users. The
default `whoami` on Windows is quite different from this implementation:
https://learn.microsoft.com/en-us/windows-server/administration/windows-commands/whoami

# Tests + Formatting
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crates/nu-std"` to run the tests for the standard library

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---------

Co-authored-by: Darren Schroeder <[email protected]>

crates/nu-command/Cargo.toml

@@ -88,6 +88,7 @@ unicode-segmentation = "1.10"
 ureq = { version = "2.8", default-features = false, features = ["charset", "gzip", "json", "native-tls"] }
 url = "2.2"
 uu_cp = "0.0.22"
+uu_whoami = "0.0.22"
 uuid = { version = "1.5", features = ["v4"] }
 wax = { version = "0.6" }
 which = { version = "5.0", optional = true }

crates/nu-command/src/default_context.rs

@@ -229,6 +229,7 @@ pub fn add_shell_command_context(mut engine_state: EngineState) -> EngineState {
             Kill,
             Sleep,
             TermSize,
+            Whoami,
         };
 
         // Date

crates/nu-command/src/platform/mod.rs

@@ -6,6 +6,7 @@ mod input;
 mod kill;
 mod sleep;
 mod term_size;
+mod whoami;
 
 pub use ansi::{Ansi, AnsiLink, AnsiStrip};
 pub use clear::Clear;
@@ -17,3 +18,4 @@ pub use input::InputListen;
 pub use kill::Kill;
 pub use sleep::Sleep;
 pub use term_size::TermSize;
+pub use whoami::Whoami;

crates/nu-command/src/platform/whoami.rs

@@ -0,0 +1,71 @@
+use nu_protocol::ast::Call;
+use nu_protocol::engine::{Command, EngineState, Stack};
+use nu_protocol::{
+    Category, Example, IntoPipelineData, PipelineData, ShellError, Signature, Type, Value,
+};
+
+#[derive(Clone)]
+pub struct Whoami;
+
+impl Command for Whoami {
+    fn name(&self) -> &str {
+        "whoami"
+    }
+
+    fn usage(&self) -> &str {
+        "Get the current username using uutils/coreutils whoami."
+    }
+
+    fn signature(&self) -> Signature {
+        Signature::build("whoami")
+            .input_output_types(vec![(Type::Nothing, Type::String)])
+            .allow_variants_without_examples(true)
+            .category(Category::Platform)
+    }
+
+    fn search_terms(&self) -> Vec<&str> {
+        vec!["username", "coreutils"]
+    }
+
+    fn run(
+        &self,
+        _engine_state: &EngineState,
+        _stack: &mut Stack,
+        call: &Call,
+        _input: PipelineData,
+    ) -> Result<PipelineData, ShellError> {
+        let output = match uu_whoami::whoami() {
+            Ok(username) => username.to_string_lossy().to_string(),
+            Err(err) => {
+                return Err(ShellError::GenericError(
+                    "Failed to get username".into(),
+                    err.to_string(),
+                    Some(call.head),
+                    None,
+                    Vec::new(),
+                ))
+            }
+        };
+
+        Ok(Value::string(output, call.head).into_pipeline_data())
+    }
+
+    fn examples(&self) -> Vec<Example> {
+        vec![Example {
+            description: "Get the current username",
+            example: "whoami",
+            result: None,
+        }]
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::Whoami;
+
+    #[test]
+    fn examples_work_as_expected() {
+        use crate::test_examples;
+        test_examples(Whoami {})
+    }
+}