feat: update the nushell init file and make it valid module and overlay (#5188)

* break long commands into multiple lines for readability

* fix the format of closures

We generally write `{|| ...}` instead of `{ || ...}`.

* remove the `$"--opt=(val)"` structure when possible

`starship` does not require to use `--opt=val` and so we do not
need to do that with Nushell :)

the only place where this is required is with `--status` because
`$env.LAST_EXIT_CODE` can be negative and `starship` does not
appear to *like* values of the form `-2`...
so i left this line as it was.

on the other hand, `$env.CMD_DURATION_MS` and `(term size).columns`
should be fine :relieved:

* simplify the `config` mutation with new `?` syntax

This is a new very handy feature of Nushell which gives a much
simpler command combined with `default` and `merge`.

* put all `let-env`s inside an `export-env` with `load-env`

This commit has two reasons of existing:
- i think it makes it a bit easier to read with less `let-env`s
- it transforms the *script* into both a valid module and a valid
overlay

* bump the version to `0.78` in to docs

* add a note about the init file being also a module to all docs

* tweak the documentation

* update the Nushell part of the install script

* format the vuepress config file

as previous commit 117580136d3da5e00a4ccb7ada508c8510a2e50e was
not successful, let's try to make the CI happy manually :relieved:

* remove code quotes in the `config_cmd` of Nushell

* format the style in the Nushell `warning` section

5 files changed, 49 insertions, 35 deletions

diff --git a/README.md b/README.md
index b12c1a277..96fa1e000 100644
--- a/README.md
+++ b/README.md
@@ -346,10 +346,10 @@ starship init nu | save -f ~/.cache/starship/init.nu
 And add the following to the end of your Nushell configuration (find it by running `$nu.config-path`):
 
 ```sh
-source ~/.cache/starship/init.nu
+use ~/.cache/starship/init.nu
 ```
 
-Note: Only Nushell v0.73+ is supported
+Note: Only Nushell v0.78+ is supported
 
 </details>
 
diff --git a/docs/.vuepress/config.ts b/docs/.vuepress/config.ts
index 393a2bfad..38d18333a 100644
--- a/docs/.vuepress/config.ts
+++ b/docs/.vuepress/config.ts
@@ -118,14 +118,14 @@ module.exports = defineConfig({
         ["meta", { name: "twitter:alt", content: "Starship: Cross-Shell Prompt" }],
         // Google Analytics
         [
-            'script',
+            "script",
             {
                 async: true,
-                src: 'https://www.googletagmanager.com/gtag/js?id=G-N3M0VJ9NL6',
+                src: "https://www.googletagmanager.com/gtag/js?id=G-N3M0VJ9NL6",
             },
         ],
         [
-            'script',
+            "script",
             {},
             "window.dataLayer = window.dataLayer || [];\nfunction gtag(){dataLayer.push(arguments);}\ngtag('js', new Date());\ngtag('config', 'G-N3M0VJ9NL6');",
         ],
diff --git a/docs/README.md b/docs/README.md
index 0665a4311..747b38fb8 100644
--- a/docs/README.md
+++ b/docs/README.md
@@ -138,7 +138,7 @@ description: Starship is the minimal, blazing fast, and extremely customizable p
    ::: warning
 
    This will change in the future.
-   Only Nushell v0.73+ is supported.
+   Only Nushell v0.78+ is supported.
 
    :::
 
@@ -151,8 +151,9 @@ description: Starship is the minimal, blazing fast, and extremely customizable p
    And add the following to the end of your Nushell configuration (find it by running `$nu.config-path`):
 
    ```sh
-   source ~/.cache/starship/init.nu
+   use ~/.cache/starship/init.nu
    ```
+
    #### Xonsh
 
    Add the following to the end of `~/.xonshrc`:
diff --git a/install/install.sh b/install/install.sh
index 6c1f9a2a8..494a9cbf5 100755
--- a/install/install.sh
+++ b/install/install.sh
@@ -337,12 +337,13 @@ print_install() {
       nushell )
         # shellcheck disable=SC2088
         config_file="${BOLD}your nu config file${NO_COLOR} (find it by running ${BOLD}\$nu.config-path${NO_COLOR} in Nushell)"
-        config_cmd="mkdir ~/.cache/starship
-        starship init nu | save -f ~/.cache/starship/init.nu
-        source ~/.cache/starship/init.nu"
+        config_cmd="use ~/.cache/starship/init.nu"
         warning="${warning} This will change in the future.
-  Only Nushell v0.73 or higher is supported.
-  Add the following to the end of ${BOLD}your Nushell env file${NO_COLOR} (find it by running ${BOLD}\$nu.env-path${NO_COLOR} in Nushell): \"mkdir ~/.cache/starship; starship init nu | save -f ~/.cache/starship/init.nu\""
+  Only Nushell v0.78 or higher is supported.
+  Add the following to the end of ${BOLD}your Nushell env file${NO_COLOR} (find it by running ${BOLD}\$nu.env-path${NO_COLOR} in Nushell):
+
+	mkdir ~/.cache/starship
+	starship init nu | save -f ~/.cache/starship/init.nu"
         ;;
     esac
     printf "  %s\n  %s\n  And add the following to the end of %s:\n\n\t%s\n\n" \
diff --git a/src/init/starship.nu b/src/init/starship.nu
index fd8729d29..0601e1806 100644
--- a/src/init/starship.nu
+++ b/src/init/starship.nu
@@ -1,27 +1,39 @@
-let-env STARSHIP_SHELL = "nu"
-let-env STARSHIP_SESSION_KEY = (random chars -l 16)
-let-env PROMPT_MULTILINE_INDICATOR = (^::STARSHIP:: prompt --continuation)
+# this file is both a valid
+# - overlay which can be loaded with `overlay use starship.nu`
+# - module which can be used with `use starship.nu`
+# - script which can be used with `source starship.nu`
+export-env { load-env {
+    STARSHIP_SHELL: "nu"
+    STARSHIP_SESSION_KEY: (random chars -l 16)
+    PROMPT_MULTILINE_INDICATOR: (
+        ^::STARSHIP:: prompt --continuation
+    )
 
-# Does not play well with default character module.
-# TODO: Also Use starship vi mode indicators?
-let-env PROMPT_INDICATOR = ""
+    # Does not play well with default character module.
+    # TODO: Also Use starship vi mode indicators?
+    PROMPT_INDICATOR: ""
 
-let-env PROMPT_COMMAND = { ||
-    # jobs are not supported
-    let width = (term size).columns
-    ^::STARSHIP:: prompt $"--cmd-duration=($env.CMD_DURATION_MS)" $"--status=($env.LAST_EXIT_CODE)" $"--terminal-width=($width)"
-}
+    PROMPT_COMMAND: {||
+        # jobs are not supported
+        (
+            ^::STARSHIP:: prompt
+                --cmd-duration $env.CMD_DURATION_MS
+                $"--status=($env.LAST_EXIT_CODE)"
+                --terminal-width (term size).columns
+        )
+    }
 
-# Whether we have config items
-let has_config_items = (not ($env | get -i config | is-empty))
+    config: ($env.config? | default {} | merge {
+        render_right_prompt_on_last_line: true
+    })
 
-let-env config = if $has_config_items {
-    $env.config | upsert render_right_prompt_on_last_line true
-} else {
-    {render_right_prompt_on_last_line: true}
-}
-
-let-env PROMPT_COMMAND_RIGHT = { ||
-    let width = (term size).columns
-    ^::STARSHIP:: prompt --right $"--cmd-duration=($env.CMD_DURATION_MS)" $"--status=($env.LAST_EXIT_CODE)" $"--terminal-width=($width)"
-}
+    PROMPT_COMMAND_RIGHT: {||
+        (
+            ^::STARSHIP:: prompt
+                --right
+                --cmd-duration $env.CMD_DURATION_MS
+                $"--status=($env.LAST_EXIT_CODE)"
+                --terminal-width (term size).columns
+        )
+    }
+}}