Command: Add config env/nu --default to print defaults (#10480)

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# Description
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Closes #5436

When I opened this issue more than a year ago, I mainly wanted the
following capacity: easily access the full env and have the hability to
update it when a new version of `nushell` comes out.

With this PR I can now do the following:

```nu
source-env ~/.config/nushell/defaults/env.nu
source     ~/.config/nushell/defaults/config.nu

# Update nushell default config & env file (run this after a version update)
def update-defaults [] {
    config env --default | save -f ~/.config/nushell/defaults/env.nu
    config nu  --default | save -f ~/.config/nushell/defaults/config.nu
}
```

Which is more than enough for me. Along with `nushell` respecting the
XDG spec on macOS (`dirs-next` should be banned for CLI tools on macOS),
this should be one of the last hurdle before fully switching for me!

# User-Facing Changes
<!-- List of all changes that impact the user experience here. This
helps us keep track of breaking changes. -->

Two new switches to existing commands:

```nu
config env --default # Print the default env embedded at compile time in the binary
config nu  --default # Print the default config embedded at compile time in the binary
```

# Tests + Formatting
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- `cargo run -- -c "use std testing; testing run-tests --path
crates/nu-std"` to run the tests for the standard library

> **Note**
> from `nushell` you can also use the `toolkit` as follows
> ```bash
> use toolkit.nu # or use an `env_change` hook to activate it
automatically
> toolkit check pr
> ```
-->

- Added a test for the output of `config env --default`
- Added a test for the output of `config nu --default`

# After Submitting
<!-- If your PR had any user-facing changes, update [the
documentation](https://github.com/nushell/nushell.github.io) after the
PR is merged, if necessary. This will help us keep the docs up to date.
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Are the docs for commands generated automatically or do I need to make a
PR there too ? It's no problem if so, just point me at instructions if
there are any :)

crates/nu-command/src/env/config/config_env.rs

@@ -2,7 +2,7 @@ use nu_engine::env_to_strings;
 use nu_protocol::{
     ast::Call,
     engine::{Command, EngineState, Stack},
-    Category, Example, PipelineData, ShellError, Signature, Type,
+    Category, Example, IntoPipelineData, PipelineData, ShellError, Signature, Type, Value,
 };
 
 use super::utils::{gen_command, get_editor};
@@ -18,7 +18,11 @@ impl Command for ConfigEnv {
     fn signature(&self) -> Signature {
         Signature::build(self.name())
             .category(Category::Env)
-            .input_output_types(vec![(Type::Nothing, Type::Nothing)])
+            .input_output_types(vec![
+                (Type::Nothing, Type::Nothing),
+                (Type::Nothing, Type::String),
+            ])
+            .switch("default", "Print default `env.nu` file instead.", Some('d'))
         // TODO: Signature narrower than what run actually supports theoretically
     }
 
@@ -27,11 +31,23 @@ impl Command for ConfigEnv {
     }
 
     fn examples(&self) -> Vec<Example> {
-        vec![Example {
+        vec![
+            Example {
                 description: "allow user to open and update nu env",
                 example: "config env",
                 result: None,
-        }]
+            },
+            Example {
+                description: "allow user to print default `env.nu` file",
+                example: "config env --default,",
+                result: None,
+            },
+            Example {
+                description: "allow saving the default `env.nu` locally",
+                example: "config env --default | save -f ~/.config/nushell/default_env.nu",
+                result: None,
+            },
+        ]
     }
 
     fn run(
@@ -41,6 +57,12 @@ impl Command for ConfigEnv {
         call: &Call,
         input: PipelineData,
     ) -> Result<PipelineData, ShellError> {
+        // `--default` flag handling
+        if call.has_flag("default") {
+            let head = call.head;
+            return Ok(Value::string(nu_utils::get_default_env(), head).into_pipeline_data());
+        }
+
         let env_vars_str = env_to_strings(engine_state, stack)?;
         let nu_config = match engine_state.get_config_path("env-path") {
             Some(path) => path.clone(),

crates/nu-command/src/env/config/config_nu.rs

@@ -2,7 +2,7 @@ use nu_engine::env_to_strings;
 use nu_protocol::{
     ast::Call,
     engine::{Command, EngineState, Stack},
-    Category, Example, PipelineData, ShellError, Signature, Type,
+    Category, Example, IntoPipelineData, PipelineData, ShellError, Signature, Type, Value,
 };
 
 use super::utils::{gen_command, get_editor};
@@ -18,7 +18,15 @@ impl Command for ConfigNu {
     fn signature(&self) -> Signature {
         Signature::build(self.name())
             .category(Category::Env)
-            .input_output_types(vec![(Type::Nothing, Type::Nothing)])
+            .input_output_types(vec![
+                (Type::Nothing, Type::Nothing),
+                (Type::Nothing, Type::String),
+            ])
+            .switch(
+                "default",
+                "Print default `config.nu` file instead.",
+                Some('d'),
+            )
         // TODO: Signature narrower than what run actually supports theoretically
     }
 
@@ -27,11 +35,23 @@ impl Command for ConfigNu {
     }
 
     fn examples(&self) -> Vec<Example> {
-        vec![Example {
+        vec![
+            Example {
                 description: "allow user to open and update nu config",
                 example: "config nu",
                 result: None,
-        }]
+            },
+            Example {
+                description: "allow user to print default `config.nu` file",
+                example: "config nu --default,",
+                result: None,
+            },
+            Example {
+                description: "allow saving the default `config.nu` locally",
+                example: "config nu --default | save -f ~/.config/nushell/default_config.nu",
+                result: None,
+            },
+        ]
     }
 
     fn run(
@@ -41,6 +61,12 @@ impl Command for ConfigNu {
         call: &Call,
         input: PipelineData,
     ) -> Result<PipelineData, ShellError> {
+        // `--default` flag handling
+        if call.has_flag("default") {
+            let head = call.head;
+            return Ok(Value::string(nu_utils::get_default_config(), head).into_pipeline_data());
+        }
+
         let env_vars_str = env_to_strings(engine_state, stack)?;
         let nu_config = match engine_state.get_config_path("config-path") {
             Some(path) => path.clone(),

crates/nu-command/tests/commands/config_env_default.rs

@@ -0,0 +1,11 @@
+use nu_test_support::nu;
+
+#[test]
+fn print_config_env_default_to_stdout() {
+    let actual = nu!("config env --default");
+    assert_eq!(
+        actual.out,
+        nu_utils::get_default_env().replace(['\n', '\r'], "")
+    );
+    assert!(actual.err.is_empty());
+}

crates/nu-command/tests/commands/config_nu_default.rs

@@ -0,0 +1,11 @@
+use nu_test_support::nu;
+
+#[test]
+fn print_config_nu_default_to_stdout() {
+    let actual = nu!("config nu --default");
+    assert_eq!(
+        actual.out,
+        nu_utils::get_default_config().replace(['\n', '\r'], "")
+    );
+    assert!(actual.err.is_empty());
+}

crates/nu-command/tests/commands/mod.rs

@@ -7,6 +7,8 @@ mod break_;
 mod cal;
 mod cd;
 mod compact;
+mod config_env_default;
+mod config_nu_default;
 mod continue_;
 mod conversions;
 mod cp;